Research Article Characterization of the Polycaprolactone...

10
Research Article Characterization of the Polycaprolactone Melt Crystallization: Complementary Optical Microscopy, DSC, and AFM Studies V. Speranza, 1 A. Sorrentino, 2 F. De Santis, 1 and R. Pantani 1 1 Department of Industrial Engineering (DIIN), University of Salerno, Via Giovanni Paolo II, 84084 Fisciano, Italy 2 Institute for Composite and Biomedical Materials (IMCB), National Research Council (CNR), Piazzale Enrico Fermi 1, 80055 Portici, Italy Correspondence should be addressed to A. Sorrentino; [email protected] Received 28 August 2013; Accepted 8 October 2013; Published 9 January 2014 Academic Editors: V. Amig´ o, P. Reis, and S. Wu Copyright © 2014 V. Speranza et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. e first stages of the crystallization of polycaprolactone (PCL) were studied using several techniques. e crystallization exotherms measured by differential scanning calorimetry (DSC) were analyzed and compared with results obtained by polarized optical microscopy (POM), rheology, and atomic force microscope (AFM). e experimental results suggest a strong influence of the observation scale. In particular, the AFM, even if limited on time scale, appears to be the most sensitive technique to detect the first stages of crystallization. On the contrary, at least in the case analysed in this work, rheology appears to be the least sensitive technique. DSC and POM provide closer results. is suggests that the definition of induction time in the polymer crystallization is a vague concept that, in any case, requires the definition of the technique used for its characterization. 1. Introduction e phenomenon of crystallization of polymers has been studied since the start of the macromolecular science. Despite the great efforts spent by the scientific community on this topic, the formation of crystalline structures between high- entan-gled polymer chains is still debated. A complete investigation of the crystallization process requires the use of several analytical techniques, since a single technique does not supply sufficient understanding of the complex multiscale transformation. Heat transition involved in the process is typically measured by differential scanning calorimeter (DSC-DTA), structures formation is generally monitored by microscopy (optical, AFM, TEM, or SEM), and order alteration is observed by X-ray diffraction and infrared spectroscopy, whereas changes in flow properties are commonly measured with rheological tests [1, 2]. However, an accurate comparison of the quantities measured on indi- vidual instruments is not straightforward, since not only the scale but also the samples conditions are always different. e application of atomic force microscopy (AFM) to polymer system is oſten devoted to the observation of a solidified sample aſter quenching the crystal structure, as a static subsequent step. Most dynamic hot stage studies of morphological development in situ have been performed using optical microscopy, with its limited resolution. Recently, the possibility to follow real-time dynamics of processes at nanoscale, even if limited on time scale, is opened to AFM. Since the initial in situ observations of the polymer crystallization reported by Pearce and Vancso [35] and by Schultz and Miles [6] several additional real-time AFM studies were reported [714]. Some of these studies were per- formed by controlling the temperature of the sample [10, 11] and sometimes the temperature of the AFM tip [13, 14]. Pearce and Vancso [3, 4] first reported the consistency of in situ AFM results with conventional optical microscopy results. ey found that growth rates of individual lamellae agree with results obtained at lower magnification by optical microscopy. Similar growth rates were observed at the growth front by Hobbs et al. [9] whereas observations at the scale of the lamella revealed for the first time that dominant lamellae do not grow at a constant rate. Lamellae grow at sporadic or constant rates depending on the presence or not of surround- ing lamellae competing at the growth front [10, 11, 14]. Hindawi Publishing Corporation e Scientific World Journal Volume 2014, Article ID 720157, 9 pages http://dx.doi.org/10.1155/2014/720157

Transcript of Research Article Characterization of the Polycaprolactone...

Page 1: Research Article Characterization of the Polycaprolactone ...downloads.hindawi.com/journals/tswj/2014/720157.pdfe application of atomic force microscopy (AFM) to polymer system is

Research ArticleCharacterization of the Polycaprolactone Melt CrystallizationComplementary Optical Microscopy DSC and AFM Studies

V Speranza1 A Sorrentino2 F De Santis1 and R Pantani1

1 Department of Industrial Engineering (DIIN) University of Salerno Via Giovanni Paolo II 84084 Fisciano Italy2 Institute for Composite and Biomedical Materials (IMCB) National Research Council (CNR)Piazzale Enrico Fermi 1 80055 Portici Italy

Correspondence should be addressed to A Sorrentino asorrentunisait

Received 28 August 2013 Accepted 8 October 2013 Published 9 January 2014

Academic Editors V Amigo P Reis and S Wu

Copyright copy 2014 V Speranza et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

The first stages of the crystallization of polycaprolactone (PCL)were studied using several techniquesThe crystallization exothermsmeasured by differential scanning calorimetry (DSC) were analyzed and compared with results obtained by polarized opticalmicroscopy (POM) rheology and atomic force microscope (AFM) The experimental results suggest a strong influence of theobservation scale In particular the AFM even if limited on time scale appears to be the most sensitive technique to detect thefirst stages of crystallization On the contrary at least in the case analysed in this work rheology appears to be the least sensitivetechnique DSC and POM provide closer results This suggests that the definition of induction time in the polymer crystallizationis a vague concept that in any case requires the definition of the technique used for its characterization

1 Introduction

The phenomenon of crystallization of polymers has beenstudied since the start of themacromolecular science Despitethe great efforts spent by the scientific community on thistopic the formation of crystalline structures between high-entan-gled polymer chains is still debated

A complete investigation of the crystallization processrequires the use of several analytical techniques since a singletechnique does not supply sufficient understanding of thecomplex multiscale transformation Heat transition involvedin the process is typically measured by differential scanningcalorimeter (DSC-DTA) structures formation is generallymonitored by microscopy (optical AFM TEM or SEM)and order alteration is observed by X-ray diffraction andinfrared spectroscopy whereas changes in flow properties arecommonly measured with rheological tests [1 2] Howeveran accurate comparison of the quantities measured on indi-vidual instruments is not straightforward since not only thescale but also the samples conditions are always different

The application of atomic force microscopy (AFM) topolymer system is often devoted to the observation of a

solidified sample after quenching the crystal structure as astatic subsequent step Most dynamic hot stage studies ofmorphological development in situ have been performedusing optical microscopy with its limited resolution

Recently the possibility to follow real-time dynamics ofprocesses at nanoscale even if limited on time scale is openedto AFM Since the initial in situ observations of the polymercrystallization reported by Pearce and Vancso [3ndash5] andby Schultz and Miles [6] several additional real-time AFMstudies were reported [7ndash14] Some of these studies were per-formed by controlling the temperature of the sample [10 11]and sometimes the temperature of the AFM tip [13 14]

Pearce and Vancso [3 4] first reported the consistencyof in situ AFM results with conventional optical microscopyresults They found that growth rates of individual lamellaeagree with results obtained at lower magnification by opticalmicroscopy Similar growth rates were observed at the growthfront by Hobbs et al [9] whereas observations at the scale ofthe lamella revealed for the first time that dominant lamellaedo not grow at a constant rate Lamellae grow at sporadic orconstant rates depending on the presence or not of surround-ing lamellae competing at the growth front [10 11 14]

Hindawi Publishing Corporatione Scientific World JournalVolume 2014 Article ID 720157 9 pageshttpdxdoiorg1011552014720157

2 The Scientific World Journal

In situ AFM studies gave the opportunity to observedevelopingmorphologies at a lamellar scale from the genera-tion of the primary stable nucleus [8] to the development ofdominant lamellae followed by the birth of branching lamel-lae that splay leading to the spherulitic morphology [4 6 8]with finally impingement of adjacent spherulites [5]

These observations highlighted the roughness of thegrowth front seen as being smooth at the larger scale ofoptical microscopy [9]

In particular for the investigation of material transfor-mations that are associated with changes in rheological andthermal properties such as melting and crystallization anaccurate comparison between these techniques is crucial Inthe literature a few attempts for combining morphologycalorimetry and rheology can be found [15]

Martins et al [16] developed a shear differential thermalanalyzer that allowed for applying controlled shear pulsesduring isothermal or nonisothermal solidification of poly-mers Hereto a capillary rheometer and a differential thermalanalyzer were combined into a single device The instrumenthas two capillaries one for the investigated sample and onefor a reference material which are placed inside two separateidentical ovens

Nagatake et al [17] modified a commercial rheometer byadding two thermocouples on the base plate which allowedthe measurement of differences between sample and baseplate temperatures

In this paper the investigation of the morphology devel-opment of melt-grown crystal lamellae of polycaprolactoneby real-time hot stage AFM is reported The morphologicalinsights are also investigated by using polarized opticalmicroscopy (POM) differential scanning calorimetry andrheology tests

2 Experimental

21 Material The polymer investigated in this work is poly-caprolactone (119872

11989970000ndash90000 by GPC 119872

119908119872119899lt 2

density 1145 gmL at 25∘C) supplied by Sigma Aldrich

22 Differential Scanning Calorimetry A differential scan-ning calorimeter DSC 822 fromMettler Toledo Inc was usedfor determination and measurement of the calorimetricbehavior of PCLThe calibration of the temperature was donewith the extrapolated onset temperature of the phase tran-sition of indium The samples with a weight of about 10 mgwere put into an aluminum pan All the experiments wereconducted in nitrogen (flow rate 50mLmin) in order toprevent oxidative degradation

23 Optical Microscopy A PCL thin film of about 100 120583m issandwiched between two cover glasses and this is observedin light transmission using an optical Olympus BX51 Micro-scope equipped with digital camera To apply the same ther-mal protocol to the glasspolymer system a special calorime-ter (LinkamDSC600 calibratedwith indium cooledwith liq-uid nitrogen and purged with nitrogen [18]) was adopted forthe experimentsThemorphology and the isothermal growth

of the crystalline structures were observed using the micro-scope coupled to the LinkamDSC600 during the calorimetrictests

24 Atomic Force Microscopy In order to characterize thelocal morphology of the samples a Veeco Dimension 3100AFM with Nanoscope III controller was adopted All thesample images were kept using the tapping mode in order tominimize the interaction with the sample surface Two testswere conducted with the same thermal history but analyzingdifferent surfaces one test explored a square surface havinga side of 10120583m and the other one a square surface having aside of 30 120583m In both experiments the scan rate was 2Hzand 256 sample linesTheLinkamhot stage THMS600 is usedfor conditioning the sample during the in situ AFM charac-terization The equilibrium melting temperature of PCL isrelatively low about 60∘C so that it was possible to performtheAFMacquisitionwithout altering the linearity of theAFMpiezo

25 Rheological Tests Rheological experiments were per-formed using a stress controlled rotational rheometer(HAAKE RheoScope) equipped with 25mm parallel platesand using a gap thickness of 01mm To follow both thecooling process and the isothermal crystallization the evolu-tion of the mechanical properties has been monitored by anoscillatory test at the constant stress 120590 = 100Pa andconstant frequency 120596 = 01 radsec The choice of thesevalues is crucial in order to reduce as much as possible thedisturbance during the crystallization and ensure that thewhole crystallization process occurs in the range of sensitivityof the equipment To verify whether these parameters couldaffect the experimental results tests with stress values rangingfrom 1 to 1000 Pa have been performed

Optical observations weremade directly in the rheometerby a CCD camera (HAAKE RheoScope) equipped with a 5xmagnification objective

26 Methods The same thermal history has been applied toall the experiments In particular an annealing treatment hasbeen conducted at 119879 = 120∘C for 15min The cooling stepfrom the annealing temperature (119879

119886) to the crystallization

temperature (119879119888) has been performed in two steps The first

step from 119879119886to the melting temperature 119879

119898= 60∘C was

performed at a rate compatible with the limitations of thedifferent experimental techniques (minus10∘Cminminus1 for DSCAFM and POM minus3∘Cminminus1 for rheological tests) whereasthe second step from 119879

119898to 119879119888was performed at a rate of

minus05∘Cminminus1The temperature profile has been verified by anindependent thermocouple placed inside the molten sampleThe temperature sensors of the rheometer the calorimeterand the hot stage were carefully calibrated to minimizetemperature differences among the instruments

3 Results and Discussion

31 DSC Experiments A preliminary calorimetric test wasperformed in order to determine the relevant temperatures

The Scientific World Journal 3

0

20

40

60

80

100

120

0 1000 2000 3000 4000 5000 6000Time (s)

0

005

01

015

02

025

03

035

04

Hea

t flow

(Wg

)

Tem

pera

ture

(∘C)

Figure 1 Temperature and calorimetric evolution during prelimi-nary DSC test

0

005

01

015

02

025

0 2000 4000 6000 8000 10000 12000 14000 16000Isothermal time (s)

Hea

t flow

(Wg

)

Tc = 43∘CTc = 45∘CTc = 47∘C

Tc = 49∘CTc = 50∘C

Figure 2 Experimental DSC tests

for the crystallization phenomena of PCL The sample washeated to 120∘C at 30Cmin kept at this temperature for 15minutes and then cooled down to 60∘C at minus10 Cmin andfrom 60 to 25∘C at minus05 Cmin The result of this test isreported in Figure 1

The calorimetric plot evidences an exothermic peak dueto the crystallization of PCL which starts at 44∘C has a max-imum at 39∘C and ends at 34∘C

A series of isothermal crystallization tests were thuscarried out at temperatures between 50∘C and 43∘CThe cor-responding exothermic peaks are reported in Figure 2 as afunction of the time of the isothermal step As expected byincreasing the crystallization temperature the peaks decreasein height and spread along the time axis The area delimitedby the peaks characteristic of the heat released during thecrystallization is almost constant for all the experiments

The crystallization heat obtained by the measurement ofthe area under the exothermic peak can be transformed intothe relative degree of crystallinity (120572DSC(119905)) by the division ofthe heat that develops at each crystallization time 119905 (Δ119867

119905) by

0

20

40

60

80

100

10 100 1000 10000 100000Isothermal time (s)

120572D

SC=

relat

ive c

ryst

allin

ity (mdash

) (

)

Tc = 43∘CTc = 45∘CTc = 47∘C

Tc = 49∘CTc = 50∘C

Figure 3 Evolution of relative crystallinity (120572DSC(119905) defined by (1))in isothermal crystallization

the total area under the exothermic peak that is the total heat(Δ1198670) generated up to the complete crystallization

120572DSC (119905) =int119905

0

(119889119867119889119905) 119889119905

intinfin

0

(119889119867119889119905) 119889119905

=Δ119867119905

Δ1198670

(1)

Figure 3 displays the development of 120572DSC as a functionof the isothermal time at several crystallization temperaturesA shift of the curves toward lower times and an incrementof the slope of their linear portion can be seen as thecrystallization temperature becomes lower This implies thata higher undercooling degree leads to a higher crystallizationrate

An approximation of the crystallization rate can be madeby the overall crystallization rate (1119905

05) where 119905

05(half the

crystallization time) is the time at which 120572DSC(119905) approachesthe value of 50 This parameter is proportional to both theprimary nucleation rate and the crystalspherulite growth[19]The induction time (119905

0) that is the time at which 120572DSC(119905)

starts to increase is also clear from Figure 3 As expected t0

increases exponentially with the crystallization temperature

32 POM Experiments The morphology developing duringthe crystallization of PCL was investigated by polarizedoptical microscopy (POM) The micrographs were acquiredat suitable time intervals with crossed polarizer during thesame isothermal tests performed during the DSC tests

The development of crystalline structures at 45∘C isshown in the optical micrographs reported in Figures 4 5and 6 On observing the morphology evolution by the polar-ized optical microscope it was possible to measure the evo-lution of birefringence Birefringence was then normalizedaccording to the following equation

120572POM (119905) =Δ119899 (119905) minus Δ119899

0

Δ119899infinminus Δ1198990

(2)

4 The Scientific World Journal

Figure 4 Optical image of PCL at the start of the isothermal crys-tallization (hot stage temperature = 45∘C) 50x (image dimensions175 times 1312 120583m)

Figure 5 Optical image of PCL after 1800 seconds of isothermalcrystallization (hot stage temperature = 45∘C) 50x (image dimen-sions 175 times 1312 120583m)

inwhichΔ119899 is themeasured birefringence at a given timeΔ1198990

is the birefringence at the start of the isothermal test (which isnearly zero) and Δ119899

infinis the birefringence at the end of crys-

tallization (when a plateau is reached) Being birefringenceessentially proportional to crystallinity 120572POM(119905) defined by(2) can be used to monitor the evolution of crystallization inthin samples

In Figure 7 the evolution of 120572POM is plotted as a functionof time for a series of isothermal tests similar to thosepresented in Figure 2 As the crystallization temperatureincreases the sigmoidal curves are shifted parallel to eachother on a linear-log scale At the highest temperature usedhere the time to reach the birefringence plateau has beenincreased by an order of magnitude

It is important to point out that evolution intensityexpressed by (2) does not provide a direct measure of thedegree of crystallinity Polymer crystallizing systems consistof many birefringent spots arranged in the light path eitherside by side or in series Ziabicki [20] argued that single-crystal formula (2) should be applied only to very dilutesystems andor very thin samples in which probability ofthe appearance of more than one crystal in the light path isnegligible On the other hand Binsbergen [21] developed amodel of stacks of plates with small optical retardation

Figure 6 Optical image of PCL after 3600 seconds of isothermalcrystallization (hot stage temperature = 45∘C) 50x (image dimen-sions 175 times 1312 120583m)

0

02

04

06

08

1

10 100 1000 10000 100000Isothermal time (s)

Tc = 43∘CTc = 45∘CTc = 47∘C

Tc = 49∘CTc = 50∘C

120572PO

M(t

) (mdash

)

Figure 7 Evolution of 120572POM (defined by (2)) in isothermal crystal-lization

claiming applicability of the single-crystal formula to nondi-lute systems More in general the depolarization ratio isnot proportional to crystallinity alone but to crystallinitymultiplied by a function of average plate dimensions [22]However assuming directly observable quantity 120572POM asa crystallization characteristic per se information aboutstructure formation (induction time) and structural changescan be obtained

33 Rheological Experiments In Figures 8(a) and 8(b) theevolution of the storage modulus (G1015840) the loss modulus (G10158401015840)and the complex viscosity (120578lowast) versus time during both thecooling (after the annealing process at 119879 = 120∘C) and theisothermal crystallization is reported together with the cor-responding temperature profiles for two different quiescentcrystallization tests

The experiment shows that both moduli (G1015840 and G10158401015840) aresusceptible to structural changes in the polymer As an exam-ple G1015840 after a first increase during the cooling step whichcan be ascribed to the effect of temperature shows a plateauat 119879 = 119879

119888 followed by a second increase representative of

The Scientific World Journal 5

0 1000 2000 3000 4000 5000 6000 7000Time (s)

40

55

70

85

100

115

130

Tem

pera

ture

(∘C)

1E+06

1E+05

1E+04

1E+03

1E+02

1E+01

1E+00

120578lowast

G998400998400G998400

T

G998400

(Pa)

G998400998400

(Pa)

120578lowast

(Palowast

s)

Tc = 45∘C

(a)

0 2000 4000 6000 8000 10000 12000Time (s)

40

55

70

85

100

115

130

Tem

pera

ture

(∘C)

1E+06

1E+05

1E+04

1E+03

1E+02

1E+01

1E+00

120578lowast

G998400998400G998400

T

G998400

(Pa)

G998400998400

(Pa)

120578lowast

(Palowast

s)

Tc = 47∘C

(b)

Figure 8 (a) Rheological measurements of the polycaprolactone crystallization at 45∘C storage modulus G1015840 loss modulus G10158401015840 complexviscosity 120578lowast and temperature measured simultaneously under constant stress of 100 Pa and constant frequency of 01 radsec (b) Rheologicalmeasurements of the polycaprolactone crystallization at 47∘C storage modulus G1015840 loss modulus G10158401015840 complex viscosity 120578lowast and temperaturemeasured simultaneously under constant stress of 100 Pa and constant frequency of 01 radsec

0

02

04

06

08

1

0 500 1000 1500 2000 2500 3000Isothermal time (s)

120572RH

EO(mdash

)

Tc = 45∘C

(a)

0

02

04

06

08

1

Isothermal time (s)0 1000 2000 3000 4000 5000 6000 7000 8000

120572RH

EO(mdash

)

Tc = 47∘C

(b)

Figure 9 (a) Comparison between rheological evolution and optical morphology during isothermal crystallization of PCL at 119879 = 45∘C (b)Comparison between rheological evolution and optical morphology during isothermal crystallization of PCL at 119879 = 47∘C

the crystallization process Finally a second plateau is foundwhen crystallinity reaches a maximum value

From the rheological experiment the induction time forthe isothermal crystallization can be detected at the timewhen the storage modulus abruptly increases The trans-formed crystallized fraction 120572RHEO(119905) has been estimatedfrom the time dependent 1198661015840(119905) values according to thefollowing equation [23]

120572RHEO (119905) =1198661015840

(119905) minus 1198661015840

0

1198661015840infin(119905) minus 119866

1015840

0

(3)

where 1198661015840119900 1198661015840(119905) and 1198661015840

infinare the melt stiffness values at time

0 119905 and infinity respectivelyThe results for the structure development during the

isothermal quiescent crystallization have been obtained atdifferent crystallization temperatures In Figures 9(a) and

9(b) the evolution of 120572RHEO to the isothermal crystallizationat 45∘C and 47∘C respectively is reported

The time scale starts at the end of the cooling step for boththe rheological and the morphological tests The times readfrom the figures are then directly related to the evolution ofthe crystallization in isothermal condition

The morphological investigation shows that spherulitesdevelop and growuntil the impingement occurs As expectedthe number of nuclei increases as the isothermal crystalliza-tion temperature decreases What is interesting is the com-parison between the structure development and the G1015840 trend(Figures 9(a) and 9(b)) Indeed in all the cases it hasbeen observed that spherulites appear and grow when thestorage modulus is still constant at the first plateau value(representative of G1015840 for the undercooled melt at 119879

119888) This

result is in agreement with the results reported by Aciernoet al [24] Bove and Nobile [25] and Pogodina et al [26]

6 The Scientific World Journal

100

75

50

25

00 25 50 75 100

t = 1300 s

(a)

100

75

50

25

00 25 50 75 100

t = 2000 s

(b)

100

75

50

25

00 25 50 75 100

t = 2500 s

(c)

100

75

50

25

00 25 50 75 100

t = 2900 s

(d)

100

75

50

25

00 25 50 75 100

t = 4100 s

(e)

Figure 10 AFM amplitude images on a square area with sides of 10120583m (119879119888= 50∘C)

The Scientific World Journal 7

The increase in G1015840 during time after the impingement is stillrelated to the crystallization process itself

34 AFM Experiments The same thermal protocol adoptedbefore was replicated during AFM measurements In thatcase however the recording of the data starts in parallelwith the second cooling step (T lt 60∘C) In contrast to thatobserved with the calorimetric experiments the first signalof structures formation was observed during the secondcooling step at temperatures just below 50∘C For that it wasimpossible to carry out isothermal AFM tests at temperaturelower than 50∘C

The evolution of the samples surface morphology wasrecoded in terms of distance from a reference position(height) and the characteristic oscillation (amplitude andphase) of the AFM cantilever during the observation timesThe three acquired signals are strictly related to the structureformation on the sample surface during the crystallizationphenomena However in our case the amplitude signal wasfound themost sensible to the change in surfacemorphology

For the present analysis two different tests were consid-ered one with an observed square area with a side of 10 120583mand another withwider area having a side of 30 120583mAs shownin Figure 10 some evidence of crystalline structures appearson the surface after about 1500 s in isothermal conditions

The crystalline structure development was followed byAFM while growing and it was found that the growth frontpropagates by the advancement of primary arms with theregions between the arms filled in by secondary arms growingbehind the primary front [27]

During the isothermal step new crystal aggregates werenot formed but just the development of the previously formedstructures was evident This observation is coherent with thehypothesis of nucleation dependence on temperature andthus during the isothermal step no new stable nuclei areformed

The development of new crystalline structures on thesample surface was followed by means of the evolution of theaverage value of the amplitude signal 119860(119905) during the wholetest

In particular by assuming as initial value of the averagedamplitude (119860

0) the value that 119860(119905) assumes at starting crys-

tallization time the variations of the averaged amplitude foreach time (119860(119905) minus119860

0) divided by the total variation recorded

during the whole test can be transformed into a variationindex (120572AFM(119905))

120572AFM (119905) =int119905

0

(119860 (119905) minus 1198600) 119889119905

intinfin

0

(119860 (119905) minus 1198600) 119889119905

(4)

In Figure 11 is reported for both tests conditions the evo-lution of 120572AFM(119905) as function of the isothermal crystallizationtime

At early stage of the crystallization process a small part ofthe investigated surface is covered by crystalline structure sothe variations of the averaged amplitude signal are very lowAs the crystallization proceeds the variations of the averagedamplitude become larger until a large part of the surface is

0

20

40

60

80

100

0 2000 4000 6000 8000 10000 12000Isothermal time (s)

120572A

FM(mdash

) (

)

10120583m30120583m

Figure 11 Evolution of averaged amplitude of AFM test on a squarearea with sides of 10120583m and 30 120583m

covered by the crystalline structure and therefore the varia-tions of the averaged amplitude are constant

As expected even on the same sample the morphologyappears very different by changing the surface analyzed Thisis clearly shown in Figure 12 where the same sample shows adifferent texture by changing the scanned area

4 Discussions

All the techniques adopted in this work were analysed insuch a way to obtain sigmoidal curves representative of theevolution of the crystallization From all the curves it waspossible to identify an induction time as the time at which themeasured signal deviates from the value that it presents at thestart of the isothermal step when the sample is still moltenwithout any crystallinity A comparison between the resultsobtained with the different techniques presented is shown inFigure 13

Results clearly reveal that the induction time found on theentire range of crystallization is dependent on the techniqueused As expected the observation scale plays an importantrole in its determination Rheology appears to be the leastsensitive technique probably because in order to measurean increase in rheological parameters an interaction amongcrystals is necessary On the contrary AFM tests that are ableto resolve the surface sample at dimensions comparable to theprimary nuclei can detect crystallization at initial stages

5 Conclusions

The morphological development taking place during thecrystallization of polycaprolactone (PCL) was studied usingseveral techniques

Results show that the induction time is dependent on thetechnique used As expected the observation scale plays animportant role in its determination In particular despite itslimitations the AFM that is able to resolve the surface sampleat dimensions comparable to the primary nuclei is able

8 The Scientific World Journal

100

75

50

25

00 25 50 75 100

(120583m)

(a)

300

200

100

00 100 200 300

(120583m)

(b)

Figure 12 AFM amplitude images on different areas after complete crystallization

10

100

1000

10000

41 42 43 44 45 46 47 48 49 50 51

Indu

ctio

n tim

e (s)

DSCPOMRheology

Temperature (∘C)

AFM 10120583mAFM 30120583m

Figure 13 Induction time recorder by the different techniques Thedashed line represents a guide for eyes

to detect crystallization at initial stages On the contraryrheology appears to be the least sensitive technique probablybecause in order to measure an increase in rheologicalparameters an interaction among crystals is necessary DSCand POM techniques supply closer results It suggests that thedefinition of induction time in the polymer crystallization isa vague concept that in any case requires the definition ofthe technique used for its characterization

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] R Pantani I Coccorullo V Speranza and G TitomanlioldquoModeling of morphology evolution in the injection moldingprocess of thermoplastic polymersrdquo Progress in Polymer Sciencevol 30 no 12 pp 1185ndash1222 2005

[2] R Pantani V Speranza A Sorrentino and G TitomanlioldquoMolecular orientation and strain in injectionmoulding of ther-moplasticsrdquo Macromolecular Symposia vol 185 no 1 pp 293ndash307 2002

[3] R Pearce and G J Vancso ldquoImaging of melting and crystalliza-tion of poly(ethylene oxide) in real-time by hot-stage atomicforce microscopyrdquo Macromolecules vol 30 no 19 pp 5843ndash5848 1997

[4] R Pearce and G J Vancso ldquoReal-time imaging of meltingand crystallization in poly(ethylene oxide) by atomic forcemicroscopyrdquo Polymer vol 39 no 5 pp 1237ndash1242 1998

[5] R Pearce and G J Vancso ldquoObservations of crystallizationandmelting in poly(ethylene oxide)poly(methyl methacrylate)blends by hot-stage atomic-force microscopyrdquo Journal of Poly-mer Science B vol 36 no 14 pp 2643ndash2651 1998

[6] J M Schultz and M J Miles ldquoAFM study of morphologicaldevelopment during the melt-crystallization of poly(ethyleneoxide)rdquo Journal of Polymer Science B vol 36 no 13 pp 2311ndash2325 1998

[7] T J McMaster J K Hobbs P J Barham and M J Miles ldquoAFMstudy of in situ real time polymer crystallization and spherulitestructurerdquo Probe Microscopy vol 1 no 1 pp 43ndash56 1997

[8] L Li C-M Chan K L Yeung J-X Li K-M Ng and Y LeildquoDirect observation of growth of lamellae and spherulites of asemicrystalline polymer by AFMrdquoMacromolecules vol 34 no2 pp 316ndash325 2001

[9] J K Hobbs T JMcMasterM JMiles and P J Barham ldquoDirectobservations of the growth of spherulites of poly(hydrox-ybutyrate-co-valerate) using atomic force microscopyrdquo Poly-mer vol 39 no 12 pp 2437ndash2446 1998

The Scientific World Journal 9

[10] L G M Beekmans R Valle and G J Vancso ldquoNucleation andgrowth of poly(120576-caprolactone) on poly(tetrafluoroethylene) byin-situ AFMrdquo Macromolecules vol 35 no 25 pp 9383ndash93902002

[11] W Zhou S Z D Cheng S Putthanarat et al ldquoCrystallizationmelting and morphology of syndiotactic polypropylene frac-tions 4 In situ lamellar single crystal growth and melting indifferent sectorsrdquoMacromolecules vol 33 no 18 pp 6861ndash68682000

[12] Y Jiang D-D Yan X Gao et al ldquoLamellar branching ofpoly(bisphenol A-co-decane) spherulites at different tempera-tures studied by high-temperature AFMrdquo Macromolecules vol36 no 10 pp 3652ndash3655 2003

[13] D A Ivanov Z Amalou and S N Magonov ldquoReal-time evolu-tion of the lamellar organization of poly(ethylene terephthalate)during crystallization from the melt high-temperature atomicforce microscopy studyrdquo Macromolecules vol 34 no 26 pp8944ndash8952 2001

[14] Y Kikkawa H Abe M Fujita T Iwata Y Inoue and Y DoildquoCrystal growth in poly(l-lactide) thin film revealed by insitu atomic force microscopyrdquo Macromolecular Chemistry andPhysics vol 204 no 15 pp 1822ndash1831 2003

[15] R Pantani V Speranza and G Titomanlio ldquoRelevance of crys-tallisation kinetics in the simulation of the injection moldingprocessrdquo International Polymer Processing vol 16 no 1 pp 61ndash71 2001

[16] A Martins W Zhang M Brito U Infante M Romero andF O Soares ldquoIsothermal and nonisothermal crystallization ofpolymers analysis with a shear differential thermal analyzerrdquoReview of Scientific Instruments vol 76 no 10 Article ID 1051052005

[17] W Nagatake T Takahashi Y Masubuchi J-I Takimoto andK Koyama ldquoDevelopment of shear flow thermal rheometer fordirect measurement of crystallization fraction of polymer meltsunder shear deformationrdquo Polymer vol 41 no 2 pp 523ndash5312000

[18] F de Santis A R Vietri and R Pantani ldquoMorphology evolutionduring polymer crystallization simultaneous calorimetric andoptical measurementsrdquoMacromolecular Symposia vol 234 pp7ndash12 2006

[19] A Sorrentino R Pantani and G Titomanlio ldquoKinetics ofmelting and characterization of the thermodynamic and kineticproperties of syndiotactic polystyrenerdquo Journal of PolymerScience B vol 45 no 2 pp 196ndash207 2007

[20] A Ziabicki ldquoApplicability of light transmission technique tostudies of crystalline polymers texturerdquo Kolloid-Zeitschrift ampZeitschrift fur Polymere vol 219 no 1 pp 2ndash12 1967

[21] F L Binsbergen ldquoDepolarization of linearly polarized light bya polycrystalline specimenrdquo Journal of Macromolecular ScienceB vol 4 pp 837ndash851 1970

[22] A Ziabicki and B Misztal-Faraj ldquoApplicability of light depolar-ization technique to crystallization studiesrdquoPolymer vol 46 no7 pp 2395ndash2403 2005

[23] Y P Khanna ldquoRheological mechanism and overview of nucle-ated crystallization kineticsrdquoMacromolecules vol 26 no 14 pp3639ndash3643 1993

[24] S Acierno E di Maio S Iannace and N Grizzuti ldquoStructuredevelopment during crystallization of polycaprolactonerdquo Rheo-logica Acta vol 45 no 4 pp 387ndash392 2006

[25] L Bove and M R Nobile ldquoShear-induced crystallization ofisotactic poly(1-butene)rdquoMacromolecular Symposia vol 185 no1 pp 135ndash147 2002

[26] N V Pogodina V P Lavrenko S Srinivas and H H WinterldquoRheology and structure of isotactic polypropylene near thegel point quiescent and shear-induced crystallizationrdquoPolymervol 42 no 21 pp 9031ndash9043 2001

[27] L G M Beekmans and G J Vancso ldquoReal-time crystalliza-tion study of poly(120576-caprolactone) by hot-stage atomic forcemicroscopyrdquo Polymer vol 41 no 25 pp 8975ndash8981 2000

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Journal ofNanomaterials

Page 2: Research Article Characterization of the Polycaprolactone ...downloads.hindawi.com/journals/tswj/2014/720157.pdfe application of atomic force microscopy (AFM) to polymer system is

2 The Scientific World Journal

In situ AFM studies gave the opportunity to observedevelopingmorphologies at a lamellar scale from the genera-tion of the primary stable nucleus [8] to the development ofdominant lamellae followed by the birth of branching lamel-lae that splay leading to the spherulitic morphology [4 6 8]with finally impingement of adjacent spherulites [5]

These observations highlighted the roughness of thegrowth front seen as being smooth at the larger scale ofoptical microscopy [9]

In particular for the investigation of material transfor-mations that are associated with changes in rheological andthermal properties such as melting and crystallization anaccurate comparison between these techniques is crucial Inthe literature a few attempts for combining morphologycalorimetry and rheology can be found [15]

Martins et al [16] developed a shear differential thermalanalyzer that allowed for applying controlled shear pulsesduring isothermal or nonisothermal solidification of poly-mers Hereto a capillary rheometer and a differential thermalanalyzer were combined into a single device The instrumenthas two capillaries one for the investigated sample and onefor a reference material which are placed inside two separateidentical ovens

Nagatake et al [17] modified a commercial rheometer byadding two thermocouples on the base plate which allowedthe measurement of differences between sample and baseplate temperatures

In this paper the investigation of the morphology devel-opment of melt-grown crystal lamellae of polycaprolactoneby real-time hot stage AFM is reported The morphologicalinsights are also investigated by using polarized opticalmicroscopy (POM) differential scanning calorimetry andrheology tests

2 Experimental

21 Material The polymer investigated in this work is poly-caprolactone (119872

11989970000ndash90000 by GPC 119872

119908119872119899lt 2

density 1145 gmL at 25∘C) supplied by Sigma Aldrich

22 Differential Scanning Calorimetry A differential scan-ning calorimeter DSC 822 fromMettler Toledo Inc was usedfor determination and measurement of the calorimetricbehavior of PCLThe calibration of the temperature was donewith the extrapolated onset temperature of the phase tran-sition of indium The samples with a weight of about 10 mgwere put into an aluminum pan All the experiments wereconducted in nitrogen (flow rate 50mLmin) in order toprevent oxidative degradation

23 Optical Microscopy A PCL thin film of about 100 120583m issandwiched between two cover glasses and this is observedin light transmission using an optical Olympus BX51 Micro-scope equipped with digital camera To apply the same ther-mal protocol to the glasspolymer system a special calorime-ter (LinkamDSC600 calibratedwith indium cooledwith liq-uid nitrogen and purged with nitrogen [18]) was adopted forthe experimentsThemorphology and the isothermal growth

of the crystalline structures were observed using the micro-scope coupled to the LinkamDSC600 during the calorimetrictests

24 Atomic Force Microscopy In order to characterize thelocal morphology of the samples a Veeco Dimension 3100AFM with Nanoscope III controller was adopted All thesample images were kept using the tapping mode in order tominimize the interaction with the sample surface Two testswere conducted with the same thermal history but analyzingdifferent surfaces one test explored a square surface havinga side of 10120583m and the other one a square surface having aside of 30 120583m In both experiments the scan rate was 2Hzand 256 sample linesTheLinkamhot stage THMS600 is usedfor conditioning the sample during the in situ AFM charac-terization The equilibrium melting temperature of PCL isrelatively low about 60∘C so that it was possible to performtheAFMacquisitionwithout altering the linearity of theAFMpiezo

25 Rheological Tests Rheological experiments were per-formed using a stress controlled rotational rheometer(HAAKE RheoScope) equipped with 25mm parallel platesand using a gap thickness of 01mm To follow both thecooling process and the isothermal crystallization the evolu-tion of the mechanical properties has been monitored by anoscillatory test at the constant stress 120590 = 100Pa andconstant frequency 120596 = 01 radsec The choice of thesevalues is crucial in order to reduce as much as possible thedisturbance during the crystallization and ensure that thewhole crystallization process occurs in the range of sensitivityof the equipment To verify whether these parameters couldaffect the experimental results tests with stress values rangingfrom 1 to 1000 Pa have been performed

Optical observations weremade directly in the rheometerby a CCD camera (HAAKE RheoScope) equipped with a 5xmagnification objective

26 Methods The same thermal history has been applied toall the experiments In particular an annealing treatment hasbeen conducted at 119879 = 120∘C for 15min The cooling stepfrom the annealing temperature (119879

119886) to the crystallization

temperature (119879119888) has been performed in two steps The first

step from 119879119886to the melting temperature 119879

119898= 60∘C was

performed at a rate compatible with the limitations of thedifferent experimental techniques (minus10∘Cminminus1 for DSCAFM and POM minus3∘Cminminus1 for rheological tests) whereasthe second step from 119879

119898to 119879119888was performed at a rate of

minus05∘Cminminus1The temperature profile has been verified by anindependent thermocouple placed inside the molten sampleThe temperature sensors of the rheometer the calorimeterand the hot stage were carefully calibrated to minimizetemperature differences among the instruments

3 Results and Discussion

31 DSC Experiments A preliminary calorimetric test wasperformed in order to determine the relevant temperatures

The Scientific World Journal 3

0

20

40

60

80

100

120

0 1000 2000 3000 4000 5000 6000Time (s)

0

005

01

015

02

025

03

035

04

Hea

t flow

(Wg

)

Tem

pera

ture

(∘C)

Figure 1 Temperature and calorimetric evolution during prelimi-nary DSC test

0

005

01

015

02

025

0 2000 4000 6000 8000 10000 12000 14000 16000Isothermal time (s)

Hea

t flow

(Wg

)

Tc = 43∘CTc = 45∘CTc = 47∘C

Tc = 49∘CTc = 50∘C

Figure 2 Experimental DSC tests

for the crystallization phenomena of PCL The sample washeated to 120∘C at 30Cmin kept at this temperature for 15minutes and then cooled down to 60∘C at minus10 Cmin andfrom 60 to 25∘C at minus05 Cmin The result of this test isreported in Figure 1

The calorimetric plot evidences an exothermic peak dueto the crystallization of PCL which starts at 44∘C has a max-imum at 39∘C and ends at 34∘C

A series of isothermal crystallization tests were thuscarried out at temperatures between 50∘C and 43∘CThe cor-responding exothermic peaks are reported in Figure 2 as afunction of the time of the isothermal step As expected byincreasing the crystallization temperature the peaks decreasein height and spread along the time axis The area delimitedby the peaks characteristic of the heat released during thecrystallization is almost constant for all the experiments

The crystallization heat obtained by the measurement ofthe area under the exothermic peak can be transformed intothe relative degree of crystallinity (120572DSC(119905)) by the division ofthe heat that develops at each crystallization time 119905 (Δ119867

119905) by

0

20

40

60

80

100

10 100 1000 10000 100000Isothermal time (s)

120572D

SC=

relat

ive c

ryst

allin

ity (mdash

) (

)

Tc = 43∘CTc = 45∘CTc = 47∘C

Tc = 49∘CTc = 50∘C

Figure 3 Evolution of relative crystallinity (120572DSC(119905) defined by (1))in isothermal crystallization

the total area under the exothermic peak that is the total heat(Δ1198670) generated up to the complete crystallization

120572DSC (119905) =int119905

0

(119889119867119889119905) 119889119905

intinfin

0

(119889119867119889119905) 119889119905

=Δ119867119905

Δ1198670

(1)

Figure 3 displays the development of 120572DSC as a functionof the isothermal time at several crystallization temperaturesA shift of the curves toward lower times and an incrementof the slope of their linear portion can be seen as thecrystallization temperature becomes lower This implies thata higher undercooling degree leads to a higher crystallizationrate

An approximation of the crystallization rate can be madeby the overall crystallization rate (1119905

05) where 119905

05(half the

crystallization time) is the time at which 120572DSC(119905) approachesthe value of 50 This parameter is proportional to both theprimary nucleation rate and the crystalspherulite growth[19]The induction time (119905

0) that is the time at which 120572DSC(119905)

starts to increase is also clear from Figure 3 As expected t0

increases exponentially with the crystallization temperature

32 POM Experiments The morphology developing duringthe crystallization of PCL was investigated by polarizedoptical microscopy (POM) The micrographs were acquiredat suitable time intervals with crossed polarizer during thesame isothermal tests performed during the DSC tests

The development of crystalline structures at 45∘C isshown in the optical micrographs reported in Figures 4 5and 6 On observing the morphology evolution by the polar-ized optical microscope it was possible to measure the evo-lution of birefringence Birefringence was then normalizedaccording to the following equation

120572POM (119905) =Δ119899 (119905) minus Δ119899

0

Δ119899infinminus Δ1198990

(2)

4 The Scientific World Journal

Figure 4 Optical image of PCL at the start of the isothermal crys-tallization (hot stage temperature = 45∘C) 50x (image dimensions175 times 1312 120583m)

Figure 5 Optical image of PCL after 1800 seconds of isothermalcrystallization (hot stage temperature = 45∘C) 50x (image dimen-sions 175 times 1312 120583m)

inwhichΔ119899 is themeasured birefringence at a given timeΔ1198990

is the birefringence at the start of the isothermal test (which isnearly zero) and Δ119899

infinis the birefringence at the end of crys-

tallization (when a plateau is reached) Being birefringenceessentially proportional to crystallinity 120572POM(119905) defined by(2) can be used to monitor the evolution of crystallization inthin samples

In Figure 7 the evolution of 120572POM is plotted as a functionof time for a series of isothermal tests similar to thosepresented in Figure 2 As the crystallization temperatureincreases the sigmoidal curves are shifted parallel to eachother on a linear-log scale At the highest temperature usedhere the time to reach the birefringence plateau has beenincreased by an order of magnitude

It is important to point out that evolution intensityexpressed by (2) does not provide a direct measure of thedegree of crystallinity Polymer crystallizing systems consistof many birefringent spots arranged in the light path eitherside by side or in series Ziabicki [20] argued that single-crystal formula (2) should be applied only to very dilutesystems andor very thin samples in which probability ofthe appearance of more than one crystal in the light path isnegligible On the other hand Binsbergen [21] developed amodel of stacks of plates with small optical retardation

Figure 6 Optical image of PCL after 3600 seconds of isothermalcrystallization (hot stage temperature = 45∘C) 50x (image dimen-sions 175 times 1312 120583m)

0

02

04

06

08

1

10 100 1000 10000 100000Isothermal time (s)

Tc = 43∘CTc = 45∘CTc = 47∘C

Tc = 49∘CTc = 50∘C

120572PO

M(t

) (mdash

)

Figure 7 Evolution of 120572POM (defined by (2)) in isothermal crystal-lization

claiming applicability of the single-crystal formula to nondi-lute systems More in general the depolarization ratio isnot proportional to crystallinity alone but to crystallinitymultiplied by a function of average plate dimensions [22]However assuming directly observable quantity 120572POM asa crystallization characteristic per se information aboutstructure formation (induction time) and structural changescan be obtained

33 Rheological Experiments In Figures 8(a) and 8(b) theevolution of the storage modulus (G1015840) the loss modulus (G10158401015840)and the complex viscosity (120578lowast) versus time during both thecooling (after the annealing process at 119879 = 120∘C) and theisothermal crystallization is reported together with the cor-responding temperature profiles for two different quiescentcrystallization tests

The experiment shows that both moduli (G1015840 and G10158401015840) aresusceptible to structural changes in the polymer As an exam-ple G1015840 after a first increase during the cooling step whichcan be ascribed to the effect of temperature shows a plateauat 119879 = 119879

119888 followed by a second increase representative of

The Scientific World Journal 5

0 1000 2000 3000 4000 5000 6000 7000Time (s)

40

55

70

85

100

115

130

Tem

pera

ture

(∘C)

1E+06

1E+05

1E+04

1E+03

1E+02

1E+01

1E+00

120578lowast

G998400998400G998400

T

G998400

(Pa)

G998400998400

(Pa)

120578lowast

(Palowast

s)

Tc = 45∘C

(a)

0 2000 4000 6000 8000 10000 12000Time (s)

40

55

70

85

100

115

130

Tem

pera

ture

(∘C)

1E+06

1E+05

1E+04

1E+03

1E+02

1E+01

1E+00

120578lowast

G998400998400G998400

T

G998400

(Pa)

G998400998400

(Pa)

120578lowast

(Palowast

s)

Tc = 47∘C

(b)

Figure 8 (a) Rheological measurements of the polycaprolactone crystallization at 45∘C storage modulus G1015840 loss modulus G10158401015840 complexviscosity 120578lowast and temperature measured simultaneously under constant stress of 100 Pa and constant frequency of 01 radsec (b) Rheologicalmeasurements of the polycaprolactone crystallization at 47∘C storage modulus G1015840 loss modulus G10158401015840 complex viscosity 120578lowast and temperaturemeasured simultaneously under constant stress of 100 Pa and constant frequency of 01 radsec

0

02

04

06

08

1

0 500 1000 1500 2000 2500 3000Isothermal time (s)

120572RH

EO(mdash

)

Tc = 45∘C

(a)

0

02

04

06

08

1

Isothermal time (s)0 1000 2000 3000 4000 5000 6000 7000 8000

120572RH

EO(mdash

)

Tc = 47∘C

(b)

Figure 9 (a) Comparison between rheological evolution and optical morphology during isothermal crystallization of PCL at 119879 = 45∘C (b)Comparison between rheological evolution and optical morphology during isothermal crystallization of PCL at 119879 = 47∘C

the crystallization process Finally a second plateau is foundwhen crystallinity reaches a maximum value

From the rheological experiment the induction time forthe isothermal crystallization can be detected at the timewhen the storage modulus abruptly increases The trans-formed crystallized fraction 120572RHEO(119905) has been estimatedfrom the time dependent 1198661015840(119905) values according to thefollowing equation [23]

120572RHEO (119905) =1198661015840

(119905) minus 1198661015840

0

1198661015840infin(119905) minus 119866

1015840

0

(3)

where 1198661015840119900 1198661015840(119905) and 1198661015840

infinare the melt stiffness values at time

0 119905 and infinity respectivelyThe results for the structure development during the

isothermal quiescent crystallization have been obtained atdifferent crystallization temperatures In Figures 9(a) and

9(b) the evolution of 120572RHEO to the isothermal crystallizationat 45∘C and 47∘C respectively is reported

The time scale starts at the end of the cooling step for boththe rheological and the morphological tests The times readfrom the figures are then directly related to the evolution ofthe crystallization in isothermal condition

The morphological investigation shows that spherulitesdevelop and growuntil the impingement occurs As expectedthe number of nuclei increases as the isothermal crystalliza-tion temperature decreases What is interesting is the com-parison between the structure development and the G1015840 trend(Figures 9(a) and 9(b)) Indeed in all the cases it hasbeen observed that spherulites appear and grow when thestorage modulus is still constant at the first plateau value(representative of G1015840 for the undercooled melt at 119879

119888) This

result is in agreement with the results reported by Aciernoet al [24] Bove and Nobile [25] and Pogodina et al [26]

6 The Scientific World Journal

100

75

50

25

00 25 50 75 100

t = 1300 s

(a)

100

75

50

25

00 25 50 75 100

t = 2000 s

(b)

100

75

50

25

00 25 50 75 100

t = 2500 s

(c)

100

75

50

25

00 25 50 75 100

t = 2900 s

(d)

100

75

50

25

00 25 50 75 100

t = 4100 s

(e)

Figure 10 AFM amplitude images on a square area with sides of 10120583m (119879119888= 50∘C)

The Scientific World Journal 7

The increase in G1015840 during time after the impingement is stillrelated to the crystallization process itself

34 AFM Experiments The same thermal protocol adoptedbefore was replicated during AFM measurements In thatcase however the recording of the data starts in parallelwith the second cooling step (T lt 60∘C) In contrast to thatobserved with the calorimetric experiments the first signalof structures formation was observed during the secondcooling step at temperatures just below 50∘C For that it wasimpossible to carry out isothermal AFM tests at temperaturelower than 50∘C

The evolution of the samples surface morphology wasrecoded in terms of distance from a reference position(height) and the characteristic oscillation (amplitude andphase) of the AFM cantilever during the observation timesThe three acquired signals are strictly related to the structureformation on the sample surface during the crystallizationphenomena However in our case the amplitude signal wasfound themost sensible to the change in surfacemorphology

For the present analysis two different tests were consid-ered one with an observed square area with a side of 10 120583mand another withwider area having a side of 30 120583mAs shownin Figure 10 some evidence of crystalline structures appearson the surface after about 1500 s in isothermal conditions

The crystalline structure development was followed byAFM while growing and it was found that the growth frontpropagates by the advancement of primary arms with theregions between the arms filled in by secondary arms growingbehind the primary front [27]

During the isothermal step new crystal aggregates werenot formed but just the development of the previously formedstructures was evident This observation is coherent with thehypothesis of nucleation dependence on temperature andthus during the isothermal step no new stable nuclei areformed

The development of new crystalline structures on thesample surface was followed by means of the evolution of theaverage value of the amplitude signal 119860(119905) during the wholetest

In particular by assuming as initial value of the averagedamplitude (119860

0) the value that 119860(119905) assumes at starting crys-

tallization time the variations of the averaged amplitude foreach time (119860(119905) minus119860

0) divided by the total variation recorded

during the whole test can be transformed into a variationindex (120572AFM(119905))

120572AFM (119905) =int119905

0

(119860 (119905) minus 1198600) 119889119905

intinfin

0

(119860 (119905) minus 1198600) 119889119905

(4)

In Figure 11 is reported for both tests conditions the evo-lution of 120572AFM(119905) as function of the isothermal crystallizationtime

At early stage of the crystallization process a small part ofthe investigated surface is covered by crystalline structure sothe variations of the averaged amplitude signal are very lowAs the crystallization proceeds the variations of the averagedamplitude become larger until a large part of the surface is

0

20

40

60

80

100

0 2000 4000 6000 8000 10000 12000Isothermal time (s)

120572A

FM(mdash

) (

)

10120583m30120583m

Figure 11 Evolution of averaged amplitude of AFM test on a squarearea with sides of 10120583m and 30 120583m

covered by the crystalline structure and therefore the varia-tions of the averaged amplitude are constant

As expected even on the same sample the morphologyappears very different by changing the surface analyzed Thisis clearly shown in Figure 12 where the same sample shows adifferent texture by changing the scanned area

4 Discussions

All the techniques adopted in this work were analysed insuch a way to obtain sigmoidal curves representative of theevolution of the crystallization From all the curves it waspossible to identify an induction time as the time at which themeasured signal deviates from the value that it presents at thestart of the isothermal step when the sample is still moltenwithout any crystallinity A comparison between the resultsobtained with the different techniques presented is shown inFigure 13

Results clearly reveal that the induction time found on theentire range of crystallization is dependent on the techniqueused As expected the observation scale plays an importantrole in its determination Rheology appears to be the leastsensitive technique probably because in order to measurean increase in rheological parameters an interaction amongcrystals is necessary On the contrary AFM tests that are ableto resolve the surface sample at dimensions comparable to theprimary nuclei can detect crystallization at initial stages

5 Conclusions

The morphological development taking place during thecrystallization of polycaprolactone (PCL) was studied usingseveral techniques

Results show that the induction time is dependent on thetechnique used As expected the observation scale plays animportant role in its determination In particular despite itslimitations the AFM that is able to resolve the surface sampleat dimensions comparable to the primary nuclei is able

8 The Scientific World Journal

100

75

50

25

00 25 50 75 100

(120583m)

(a)

300

200

100

00 100 200 300

(120583m)

(b)

Figure 12 AFM amplitude images on different areas after complete crystallization

10

100

1000

10000

41 42 43 44 45 46 47 48 49 50 51

Indu

ctio

n tim

e (s)

DSCPOMRheology

Temperature (∘C)

AFM 10120583mAFM 30120583m

Figure 13 Induction time recorder by the different techniques Thedashed line represents a guide for eyes

to detect crystallization at initial stages On the contraryrheology appears to be the least sensitive technique probablybecause in order to measure an increase in rheologicalparameters an interaction among crystals is necessary DSCand POM techniques supply closer results It suggests that thedefinition of induction time in the polymer crystallization isa vague concept that in any case requires the definition ofthe technique used for its characterization

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] R Pantani I Coccorullo V Speranza and G TitomanlioldquoModeling of morphology evolution in the injection moldingprocess of thermoplastic polymersrdquo Progress in Polymer Sciencevol 30 no 12 pp 1185ndash1222 2005

[2] R Pantani V Speranza A Sorrentino and G TitomanlioldquoMolecular orientation and strain in injectionmoulding of ther-moplasticsrdquo Macromolecular Symposia vol 185 no 1 pp 293ndash307 2002

[3] R Pearce and G J Vancso ldquoImaging of melting and crystalliza-tion of poly(ethylene oxide) in real-time by hot-stage atomicforce microscopyrdquo Macromolecules vol 30 no 19 pp 5843ndash5848 1997

[4] R Pearce and G J Vancso ldquoReal-time imaging of meltingand crystallization in poly(ethylene oxide) by atomic forcemicroscopyrdquo Polymer vol 39 no 5 pp 1237ndash1242 1998

[5] R Pearce and G J Vancso ldquoObservations of crystallizationandmelting in poly(ethylene oxide)poly(methyl methacrylate)blends by hot-stage atomic-force microscopyrdquo Journal of Poly-mer Science B vol 36 no 14 pp 2643ndash2651 1998

[6] J M Schultz and M J Miles ldquoAFM study of morphologicaldevelopment during the melt-crystallization of poly(ethyleneoxide)rdquo Journal of Polymer Science B vol 36 no 13 pp 2311ndash2325 1998

[7] T J McMaster J K Hobbs P J Barham and M J Miles ldquoAFMstudy of in situ real time polymer crystallization and spherulitestructurerdquo Probe Microscopy vol 1 no 1 pp 43ndash56 1997

[8] L Li C-M Chan K L Yeung J-X Li K-M Ng and Y LeildquoDirect observation of growth of lamellae and spherulites of asemicrystalline polymer by AFMrdquoMacromolecules vol 34 no2 pp 316ndash325 2001

[9] J K Hobbs T JMcMasterM JMiles and P J Barham ldquoDirectobservations of the growth of spherulites of poly(hydrox-ybutyrate-co-valerate) using atomic force microscopyrdquo Poly-mer vol 39 no 12 pp 2437ndash2446 1998

The Scientific World Journal 9

[10] L G M Beekmans R Valle and G J Vancso ldquoNucleation andgrowth of poly(120576-caprolactone) on poly(tetrafluoroethylene) byin-situ AFMrdquo Macromolecules vol 35 no 25 pp 9383ndash93902002

[11] W Zhou S Z D Cheng S Putthanarat et al ldquoCrystallizationmelting and morphology of syndiotactic polypropylene frac-tions 4 In situ lamellar single crystal growth and melting indifferent sectorsrdquoMacromolecules vol 33 no 18 pp 6861ndash68682000

[12] Y Jiang D-D Yan X Gao et al ldquoLamellar branching ofpoly(bisphenol A-co-decane) spherulites at different tempera-tures studied by high-temperature AFMrdquo Macromolecules vol36 no 10 pp 3652ndash3655 2003

[13] D A Ivanov Z Amalou and S N Magonov ldquoReal-time evolu-tion of the lamellar organization of poly(ethylene terephthalate)during crystallization from the melt high-temperature atomicforce microscopy studyrdquo Macromolecules vol 34 no 26 pp8944ndash8952 2001

[14] Y Kikkawa H Abe M Fujita T Iwata Y Inoue and Y DoildquoCrystal growth in poly(l-lactide) thin film revealed by insitu atomic force microscopyrdquo Macromolecular Chemistry andPhysics vol 204 no 15 pp 1822ndash1831 2003

[15] R Pantani V Speranza and G Titomanlio ldquoRelevance of crys-tallisation kinetics in the simulation of the injection moldingprocessrdquo International Polymer Processing vol 16 no 1 pp 61ndash71 2001

[16] A Martins W Zhang M Brito U Infante M Romero andF O Soares ldquoIsothermal and nonisothermal crystallization ofpolymers analysis with a shear differential thermal analyzerrdquoReview of Scientific Instruments vol 76 no 10 Article ID 1051052005

[17] W Nagatake T Takahashi Y Masubuchi J-I Takimoto andK Koyama ldquoDevelopment of shear flow thermal rheometer fordirect measurement of crystallization fraction of polymer meltsunder shear deformationrdquo Polymer vol 41 no 2 pp 523ndash5312000

[18] F de Santis A R Vietri and R Pantani ldquoMorphology evolutionduring polymer crystallization simultaneous calorimetric andoptical measurementsrdquoMacromolecular Symposia vol 234 pp7ndash12 2006

[19] A Sorrentino R Pantani and G Titomanlio ldquoKinetics ofmelting and characterization of the thermodynamic and kineticproperties of syndiotactic polystyrenerdquo Journal of PolymerScience B vol 45 no 2 pp 196ndash207 2007

[20] A Ziabicki ldquoApplicability of light transmission technique tostudies of crystalline polymers texturerdquo Kolloid-Zeitschrift ampZeitschrift fur Polymere vol 219 no 1 pp 2ndash12 1967

[21] F L Binsbergen ldquoDepolarization of linearly polarized light bya polycrystalline specimenrdquo Journal of Macromolecular ScienceB vol 4 pp 837ndash851 1970

[22] A Ziabicki and B Misztal-Faraj ldquoApplicability of light depolar-ization technique to crystallization studiesrdquoPolymer vol 46 no7 pp 2395ndash2403 2005

[23] Y P Khanna ldquoRheological mechanism and overview of nucle-ated crystallization kineticsrdquoMacromolecules vol 26 no 14 pp3639ndash3643 1993

[24] S Acierno E di Maio S Iannace and N Grizzuti ldquoStructuredevelopment during crystallization of polycaprolactonerdquo Rheo-logica Acta vol 45 no 4 pp 387ndash392 2006

[25] L Bove and M R Nobile ldquoShear-induced crystallization ofisotactic poly(1-butene)rdquoMacromolecular Symposia vol 185 no1 pp 135ndash147 2002

[26] N V Pogodina V P Lavrenko S Srinivas and H H WinterldquoRheology and structure of isotactic polypropylene near thegel point quiescent and shear-induced crystallizationrdquoPolymervol 42 no 21 pp 9031ndash9043 2001

[27] L G M Beekmans and G J Vancso ldquoReal-time crystalliza-tion study of poly(120576-caprolactone) by hot-stage atomic forcemicroscopyrdquo Polymer vol 41 no 25 pp 8975ndash8981 2000

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Page 3: Research Article Characterization of the Polycaprolactone ...downloads.hindawi.com/journals/tswj/2014/720157.pdfe application of atomic force microscopy (AFM) to polymer system is

The Scientific World Journal 3

0

20

40

60

80

100

120

0 1000 2000 3000 4000 5000 6000Time (s)

0

005

01

015

02

025

03

035

04

Hea

t flow

(Wg

)

Tem

pera

ture

(∘C)

Figure 1 Temperature and calorimetric evolution during prelimi-nary DSC test

0

005

01

015

02

025

0 2000 4000 6000 8000 10000 12000 14000 16000Isothermal time (s)

Hea

t flow

(Wg

)

Tc = 43∘CTc = 45∘CTc = 47∘C

Tc = 49∘CTc = 50∘C

Figure 2 Experimental DSC tests

for the crystallization phenomena of PCL The sample washeated to 120∘C at 30Cmin kept at this temperature for 15minutes and then cooled down to 60∘C at minus10 Cmin andfrom 60 to 25∘C at minus05 Cmin The result of this test isreported in Figure 1

The calorimetric plot evidences an exothermic peak dueto the crystallization of PCL which starts at 44∘C has a max-imum at 39∘C and ends at 34∘C

A series of isothermal crystallization tests were thuscarried out at temperatures between 50∘C and 43∘CThe cor-responding exothermic peaks are reported in Figure 2 as afunction of the time of the isothermal step As expected byincreasing the crystallization temperature the peaks decreasein height and spread along the time axis The area delimitedby the peaks characteristic of the heat released during thecrystallization is almost constant for all the experiments

The crystallization heat obtained by the measurement ofthe area under the exothermic peak can be transformed intothe relative degree of crystallinity (120572DSC(119905)) by the division ofthe heat that develops at each crystallization time 119905 (Δ119867

119905) by

0

20

40

60

80

100

10 100 1000 10000 100000Isothermal time (s)

120572D

SC=

relat

ive c

ryst

allin

ity (mdash

) (

)

Tc = 43∘CTc = 45∘CTc = 47∘C

Tc = 49∘CTc = 50∘C

Figure 3 Evolution of relative crystallinity (120572DSC(119905) defined by (1))in isothermal crystallization

the total area under the exothermic peak that is the total heat(Δ1198670) generated up to the complete crystallization

120572DSC (119905) =int119905

0

(119889119867119889119905) 119889119905

intinfin

0

(119889119867119889119905) 119889119905

=Δ119867119905

Δ1198670

(1)

Figure 3 displays the development of 120572DSC as a functionof the isothermal time at several crystallization temperaturesA shift of the curves toward lower times and an incrementof the slope of their linear portion can be seen as thecrystallization temperature becomes lower This implies thata higher undercooling degree leads to a higher crystallizationrate

An approximation of the crystallization rate can be madeby the overall crystallization rate (1119905

05) where 119905

05(half the

crystallization time) is the time at which 120572DSC(119905) approachesthe value of 50 This parameter is proportional to both theprimary nucleation rate and the crystalspherulite growth[19]The induction time (119905

0) that is the time at which 120572DSC(119905)

starts to increase is also clear from Figure 3 As expected t0

increases exponentially with the crystallization temperature

32 POM Experiments The morphology developing duringthe crystallization of PCL was investigated by polarizedoptical microscopy (POM) The micrographs were acquiredat suitable time intervals with crossed polarizer during thesame isothermal tests performed during the DSC tests

The development of crystalline structures at 45∘C isshown in the optical micrographs reported in Figures 4 5and 6 On observing the morphology evolution by the polar-ized optical microscope it was possible to measure the evo-lution of birefringence Birefringence was then normalizedaccording to the following equation

120572POM (119905) =Δ119899 (119905) minus Δ119899

0

Δ119899infinminus Δ1198990

(2)

4 The Scientific World Journal

Figure 4 Optical image of PCL at the start of the isothermal crys-tallization (hot stage temperature = 45∘C) 50x (image dimensions175 times 1312 120583m)

Figure 5 Optical image of PCL after 1800 seconds of isothermalcrystallization (hot stage temperature = 45∘C) 50x (image dimen-sions 175 times 1312 120583m)

inwhichΔ119899 is themeasured birefringence at a given timeΔ1198990

is the birefringence at the start of the isothermal test (which isnearly zero) and Δ119899

infinis the birefringence at the end of crys-

tallization (when a plateau is reached) Being birefringenceessentially proportional to crystallinity 120572POM(119905) defined by(2) can be used to monitor the evolution of crystallization inthin samples

In Figure 7 the evolution of 120572POM is plotted as a functionof time for a series of isothermal tests similar to thosepresented in Figure 2 As the crystallization temperatureincreases the sigmoidal curves are shifted parallel to eachother on a linear-log scale At the highest temperature usedhere the time to reach the birefringence plateau has beenincreased by an order of magnitude

It is important to point out that evolution intensityexpressed by (2) does not provide a direct measure of thedegree of crystallinity Polymer crystallizing systems consistof many birefringent spots arranged in the light path eitherside by side or in series Ziabicki [20] argued that single-crystal formula (2) should be applied only to very dilutesystems andor very thin samples in which probability ofthe appearance of more than one crystal in the light path isnegligible On the other hand Binsbergen [21] developed amodel of stacks of plates with small optical retardation

Figure 6 Optical image of PCL after 3600 seconds of isothermalcrystallization (hot stage temperature = 45∘C) 50x (image dimen-sions 175 times 1312 120583m)

0

02

04

06

08

1

10 100 1000 10000 100000Isothermal time (s)

Tc = 43∘CTc = 45∘CTc = 47∘C

Tc = 49∘CTc = 50∘C

120572PO

M(t

) (mdash

)

Figure 7 Evolution of 120572POM (defined by (2)) in isothermal crystal-lization

claiming applicability of the single-crystal formula to nondi-lute systems More in general the depolarization ratio isnot proportional to crystallinity alone but to crystallinitymultiplied by a function of average plate dimensions [22]However assuming directly observable quantity 120572POM asa crystallization characteristic per se information aboutstructure formation (induction time) and structural changescan be obtained

33 Rheological Experiments In Figures 8(a) and 8(b) theevolution of the storage modulus (G1015840) the loss modulus (G10158401015840)and the complex viscosity (120578lowast) versus time during both thecooling (after the annealing process at 119879 = 120∘C) and theisothermal crystallization is reported together with the cor-responding temperature profiles for two different quiescentcrystallization tests

The experiment shows that both moduli (G1015840 and G10158401015840) aresusceptible to structural changes in the polymer As an exam-ple G1015840 after a first increase during the cooling step whichcan be ascribed to the effect of temperature shows a plateauat 119879 = 119879

119888 followed by a second increase representative of

The Scientific World Journal 5

0 1000 2000 3000 4000 5000 6000 7000Time (s)

40

55

70

85

100

115

130

Tem

pera

ture

(∘C)

1E+06

1E+05

1E+04

1E+03

1E+02

1E+01

1E+00

120578lowast

G998400998400G998400

T

G998400

(Pa)

G998400998400

(Pa)

120578lowast

(Palowast

s)

Tc = 45∘C

(a)

0 2000 4000 6000 8000 10000 12000Time (s)

40

55

70

85

100

115

130

Tem

pera

ture

(∘C)

1E+06

1E+05

1E+04

1E+03

1E+02

1E+01

1E+00

120578lowast

G998400998400G998400

T

G998400

(Pa)

G998400998400

(Pa)

120578lowast

(Palowast

s)

Tc = 47∘C

(b)

Figure 8 (a) Rheological measurements of the polycaprolactone crystallization at 45∘C storage modulus G1015840 loss modulus G10158401015840 complexviscosity 120578lowast and temperature measured simultaneously under constant stress of 100 Pa and constant frequency of 01 radsec (b) Rheologicalmeasurements of the polycaprolactone crystallization at 47∘C storage modulus G1015840 loss modulus G10158401015840 complex viscosity 120578lowast and temperaturemeasured simultaneously under constant stress of 100 Pa and constant frequency of 01 radsec

0

02

04

06

08

1

0 500 1000 1500 2000 2500 3000Isothermal time (s)

120572RH

EO(mdash

)

Tc = 45∘C

(a)

0

02

04

06

08

1

Isothermal time (s)0 1000 2000 3000 4000 5000 6000 7000 8000

120572RH

EO(mdash

)

Tc = 47∘C

(b)

Figure 9 (a) Comparison between rheological evolution and optical morphology during isothermal crystallization of PCL at 119879 = 45∘C (b)Comparison between rheological evolution and optical morphology during isothermal crystallization of PCL at 119879 = 47∘C

the crystallization process Finally a second plateau is foundwhen crystallinity reaches a maximum value

From the rheological experiment the induction time forthe isothermal crystallization can be detected at the timewhen the storage modulus abruptly increases The trans-formed crystallized fraction 120572RHEO(119905) has been estimatedfrom the time dependent 1198661015840(119905) values according to thefollowing equation [23]

120572RHEO (119905) =1198661015840

(119905) minus 1198661015840

0

1198661015840infin(119905) minus 119866

1015840

0

(3)

where 1198661015840119900 1198661015840(119905) and 1198661015840

infinare the melt stiffness values at time

0 119905 and infinity respectivelyThe results for the structure development during the

isothermal quiescent crystallization have been obtained atdifferent crystallization temperatures In Figures 9(a) and

9(b) the evolution of 120572RHEO to the isothermal crystallizationat 45∘C and 47∘C respectively is reported

The time scale starts at the end of the cooling step for boththe rheological and the morphological tests The times readfrom the figures are then directly related to the evolution ofthe crystallization in isothermal condition

The morphological investigation shows that spherulitesdevelop and growuntil the impingement occurs As expectedthe number of nuclei increases as the isothermal crystalliza-tion temperature decreases What is interesting is the com-parison between the structure development and the G1015840 trend(Figures 9(a) and 9(b)) Indeed in all the cases it hasbeen observed that spherulites appear and grow when thestorage modulus is still constant at the first plateau value(representative of G1015840 for the undercooled melt at 119879

119888) This

result is in agreement with the results reported by Aciernoet al [24] Bove and Nobile [25] and Pogodina et al [26]

6 The Scientific World Journal

100

75

50

25

00 25 50 75 100

t = 1300 s

(a)

100

75

50

25

00 25 50 75 100

t = 2000 s

(b)

100

75

50

25

00 25 50 75 100

t = 2500 s

(c)

100

75

50

25

00 25 50 75 100

t = 2900 s

(d)

100

75

50

25

00 25 50 75 100

t = 4100 s

(e)

Figure 10 AFM amplitude images on a square area with sides of 10120583m (119879119888= 50∘C)

The Scientific World Journal 7

The increase in G1015840 during time after the impingement is stillrelated to the crystallization process itself

34 AFM Experiments The same thermal protocol adoptedbefore was replicated during AFM measurements In thatcase however the recording of the data starts in parallelwith the second cooling step (T lt 60∘C) In contrast to thatobserved with the calorimetric experiments the first signalof structures formation was observed during the secondcooling step at temperatures just below 50∘C For that it wasimpossible to carry out isothermal AFM tests at temperaturelower than 50∘C

The evolution of the samples surface morphology wasrecoded in terms of distance from a reference position(height) and the characteristic oscillation (amplitude andphase) of the AFM cantilever during the observation timesThe three acquired signals are strictly related to the structureformation on the sample surface during the crystallizationphenomena However in our case the amplitude signal wasfound themost sensible to the change in surfacemorphology

For the present analysis two different tests were consid-ered one with an observed square area with a side of 10 120583mand another withwider area having a side of 30 120583mAs shownin Figure 10 some evidence of crystalline structures appearson the surface after about 1500 s in isothermal conditions

The crystalline structure development was followed byAFM while growing and it was found that the growth frontpropagates by the advancement of primary arms with theregions between the arms filled in by secondary arms growingbehind the primary front [27]

During the isothermal step new crystal aggregates werenot formed but just the development of the previously formedstructures was evident This observation is coherent with thehypothesis of nucleation dependence on temperature andthus during the isothermal step no new stable nuclei areformed

The development of new crystalline structures on thesample surface was followed by means of the evolution of theaverage value of the amplitude signal 119860(119905) during the wholetest

In particular by assuming as initial value of the averagedamplitude (119860

0) the value that 119860(119905) assumes at starting crys-

tallization time the variations of the averaged amplitude foreach time (119860(119905) minus119860

0) divided by the total variation recorded

during the whole test can be transformed into a variationindex (120572AFM(119905))

120572AFM (119905) =int119905

0

(119860 (119905) minus 1198600) 119889119905

intinfin

0

(119860 (119905) minus 1198600) 119889119905

(4)

In Figure 11 is reported for both tests conditions the evo-lution of 120572AFM(119905) as function of the isothermal crystallizationtime

At early stage of the crystallization process a small part ofthe investigated surface is covered by crystalline structure sothe variations of the averaged amplitude signal are very lowAs the crystallization proceeds the variations of the averagedamplitude become larger until a large part of the surface is

0

20

40

60

80

100

0 2000 4000 6000 8000 10000 12000Isothermal time (s)

120572A

FM(mdash

) (

)

10120583m30120583m

Figure 11 Evolution of averaged amplitude of AFM test on a squarearea with sides of 10120583m and 30 120583m

covered by the crystalline structure and therefore the varia-tions of the averaged amplitude are constant

As expected even on the same sample the morphologyappears very different by changing the surface analyzed Thisis clearly shown in Figure 12 where the same sample shows adifferent texture by changing the scanned area

4 Discussions

All the techniques adopted in this work were analysed insuch a way to obtain sigmoidal curves representative of theevolution of the crystallization From all the curves it waspossible to identify an induction time as the time at which themeasured signal deviates from the value that it presents at thestart of the isothermal step when the sample is still moltenwithout any crystallinity A comparison between the resultsobtained with the different techniques presented is shown inFigure 13

Results clearly reveal that the induction time found on theentire range of crystallization is dependent on the techniqueused As expected the observation scale plays an importantrole in its determination Rheology appears to be the leastsensitive technique probably because in order to measurean increase in rheological parameters an interaction amongcrystals is necessary On the contrary AFM tests that are ableto resolve the surface sample at dimensions comparable to theprimary nuclei can detect crystallization at initial stages

5 Conclusions

The morphological development taking place during thecrystallization of polycaprolactone (PCL) was studied usingseveral techniques

Results show that the induction time is dependent on thetechnique used As expected the observation scale plays animportant role in its determination In particular despite itslimitations the AFM that is able to resolve the surface sampleat dimensions comparable to the primary nuclei is able

8 The Scientific World Journal

100

75

50

25

00 25 50 75 100

(120583m)

(a)

300

200

100

00 100 200 300

(120583m)

(b)

Figure 12 AFM amplitude images on different areas after complete crystallization

10

100

1000

10000

41 42 43 44 45 46 47 48 49 50 51

Indu

ctio

n tim

e (s)

DSCPOMRheology

Temperature (∘C)

AFM 10120583mAFM 30120583m

Figure 13 Induction time recorder by the different techniques Thedashed line represents a guide for eyes

to detect crystallization at initial stages On the contraryrheology appears to be the least sensitive technique probablybecause in order to measure an increase in rheologicalparameters an interaction among crystals is necessary DSCand POM techniques supply closer results It suggests that thedefinition of induction time in the polymer crystallization isa vague concept that in any case requires the definition ofthe technique used for its characterization

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] R Pantani I Coccorullo V Speranza and G TitomanlioldquoModeling of morphology evolution in the injection moldingprocess of thermoplastic polymersrdquo Progress in Polymer Sciencevol 30 no 12 pp 1185ndash1222 2005

[2] R Pantani V Speranza A Sorrentino and G TitomanlioldquoMolecular orientation and strain in injectionmoulding of ther-moplasticsrdquo Macromolecular Symposia vol 185 no 1 pp 293ndash307 2002

[3] R Pearce and G J Vancso ldquoImaging of melting and crystalliza-tion of poly(ethylene oxide) in real-time by hot-stage atomicforce microscopyrdquo Macromolecules vol 30 no 19 pp 5843ndash5848 1997

[4] R Pearce and G J Vancso ldquoReal-time imaging of meltingand crystallization in poly(ethylene oxide) by atomic forcemicroscopyrdquo Polymer vol 39 no 5 pp 1237ndash1242 1998

[5] R Pearce and G J Vancso ldquoObservations of crystallizationandmelting in poly(ethylene oxide)poly(methyl methacrylate)blends by hot-stage atomic-force microscopyrdquo Journal of Poly-mer Science B vol 36 no 14 pp 2643ndash2651 1998

[6] J M Schultz and M J Miles ldquoAFM study of morphologicaldevelopment during the melt-crystallization of poly(ethyleneoxide)rdquo Journal of Polymer Science B vol 36 no 13 pp 2311ndash2325 1998

[7] T J McMaster J K Hobbs P J Barham and M J Miles ldquoAFMstudy of in situ real time polymer crystallization and spherulitestructurerdquo Probe Microscopy vol 1 no 1 pp 43ndash56 1997

[8] L Li C-M Chan K L Yeung J-X Li K-M Ng and Y LeildquoDirect observation of growth of lamellae and spherulites of asemicrystalline polymer by AFMrdquoMacromolecules vol 34 no2 pp 316ndash325 2001

[9] J K Hobbs T JMcMasterM JMiles and P J Barham ldquoDirectobservations of the growth of spherulites of poly(hydrox-ybutyrate-co-valerate) using atomic force microscopyrdquo Poly-mer vol 39 no 12 pp 2437ndash2446 1998

The Scientific World Journal 9

[10] L G M Beekmans R Valle and G J Vancso ldquoNucleation andgrowth of poly(120576-caprolactone) on poly(tetrafluoroethylene) byin-situ AFMrdquo Macromolecules vol 35 no 25 pp 9383ndash93902002

[11] W Zhou S Z D Cheng S Putthanarat et al ldquoCrystallizationmelting and morphology of syndiotactic polypropylene frac-tions 4 In situ lamellar single crystal growth and melting indifferent sectorsrdquoMacromolecules vol 33 no 18 pp 6861ndash68682000

[12] Y Jiang D-D Yan X Gao et al ldquoLamellar branching ofpoly(bisphenol A-co-decane) spherulites at different tempera-tures studied by high-temperature AFMrdquo Macromolecules vol36 no 10 pp 3652ndash3655 2003

[13] D A Ivanov Z Amalou and S N Magonov ldquoReal-time evolu-tion of the lamellar organization of poly(ethylene terephthalate)during crystallization from the melt high-temperature atomicforce microscopy studyrdquo Macromolecules vol 34 no 26 pp8944ndash8952 2001

[14] Y Kikkawa H Abe M Fujita T Iwata Y Inoue and Y DoildquoCrystal growth in poly(l-lactide) thin film revealed by insitu atomic force microscopyrdquo Macromolecular Chemistry andPhysics vol 204 no 15 pp 1822ndash1831 2003

[15] R Pantani V Speranza and G Titomanlio ldquoRelevance of crys-tallisation kinetics in the simulation of the injection moldingprocessrdquo International Polymer Processing vol 16 no 1 pp 61ndash71 2001

[16] A Martins W Zhang M Brito U Infante M Romero andF O Soares ldquoIsothermal and nonisothermal crystallization ofpolymers analysis with a shear differential thermal analyzerrdquoReview of Scientific Instruments vol 76 no 10 Article ID 1051052005

[17] W Nagatake T Takahashi Y Masubuchi J-I Takimoto andK Koyama ldquoDevelopment of shear flow thermal rheometer fordirect measurement of crystallization fraction of polymer meltsunder shear deformationrdquo Polymer vol 41 no 2 pp 523ndash5312000

[18] F de Santis A R Vietri and R Pantani ldquoMorphology evolutionduring polymer crystallization simultaneous calorimetric andoptical measurementsrdquoMacromolecular Symposia vol 234 pp7ndash12 2006

[19] A Sorrentino R Pantani and G Titomanlio ldquoKinetics ofmelting and characterization of the thermodynamic and kineticproperties of syndiotactic polystyrenerdquo Journal of PolymerScience B vol 45 no 2 pp 196ndash207 2007

[20] A Ziabicki ldquoApplicability of light transmission technique tostudies of crystalline polymers texturerdquo Kolloid-Zeitschrift ampZeitschrift fur Polymere vol 219 no 1 pp 2ndash12 1967

[21] F L Binsbergen ldquoDepolarization of linearly polarized light bya polycrystalline specimenrdquo Journal of Macromolecular ScienceB vol 4 pp 837ndash851 1970

[22] A Ziabicki and B Misztal-Faraj ldquoApplicability of light depolar-ization technique to crystallization studiesrdquoPolymer vol 46 no7 pp 2395ndash2403 2005

[23] Y P Khanna ldquoRheological mechanism and overview of nucle-ated crystallization kineticsrdquoMacromolecules vol 26 no 14 pp3639ndash3643 1993

[24] S Acierno E di Maio S Iannace and N Grizzuti ldquoStructuredevelopment during crystallization of polycaprolactonerdquo Rheo-logica Acta vol 45 no 4 pp 387ndash392 2006

[25] L Bove and M R Nobile ldquoShear-induced crystallization ofisotactic poly(1-butene)rdquoMacromolecular Symposia vol 185 no1 pp 135ndash147 2002

[26] N V Pogodina V P Lavrenko S Srinivas and H H WinterldquoRheology and structure of isotactic polypropylene near thegel point quiescent and shear-induced crystallizationrdquoPolymervol 42 no 21 pp 9031ndash9043 2001

[27] L G M Beekmans and G J Vancso ldquoReal-time crystalliza-tion study of poly(120576-caprolactone) by hot-stage atomic forcemicroscopyrdquo Polymer vol 41 no 25 pp 8975ndash8981 2000

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Page 4: Research Article Characterization of the Polycaprolactone ...downloads.hindawi.com/journals/tswj/2014/720157.pdfe application of atomic force microscopy (AFM) to polymer system is

4 The Scientific World Journal

Figure 4 Optical image of PCL at the start of the isothermal crys-tallization (hot stage temperature = 45∘C) 50x (image dimensions175 times 1312 120583m)

Figure 5 Optical image of PCL after 1800 seconds of isothermalcrystallization (hot stage temperature = 45∘C) 50x (image dimen-sions 175 times 1312 120583m)

inwhichΔ119899 is themeasured birefringence at a given timeΔ1198990

is the birefringence at the start of the isothermal test (which isnearly zero) and Δ119899

infinis the birefringence at the end of crys-

tallization (when a plateau is reached) Being birefringenceessentially proportional to crystallinity 120572POM(119905) defined by(2) can be used to monitor the evolution of crystallization inthin samples

In Figure 7 the evolution of 120572POM is plotted as a functionof time for a series of isothermal tests similar to thosepresented in Figure 2 As the crystallization temperatureincreases the sigmoidal curves are shifted parallel to eachother on a linear-log scale At the highest temperature usedhere the time to reach the birefringence plateau has beenincreased by an order of magnitude

It is important to point out that evolution intensityexpressed by (2) does not provide a direct measure of thedegree of crystallinity Polymer crystallizing systems consistof many birefringent spots arranged in the light path eitherside by side or in series Ziabicki [20] argued that single-crystal formula (2) should be applied only to very dilutesystems andor very thin samples in which probability ofthe appearance of more than one crystal in the light path isnegligible On the other hand Binsbergen [21] developed amodel of stacks of plates with small optical retardation

Figure 6 Optical image of PCL after 3600 seconds of isothermalcrystallization (hot stage temperature = 45∘C) 50x (image dimen-sions 175 times 1312 120583m)

0

02

04

06

08

1

10 100 1000 10000 100000Isothermal time (s)

Tc = 43∘CTc = 45∘CTc = 47∘C

Tc = 49∘CTc = 50∘C

120572PO

M(t

) (mdash

)

Figure 7 Evolution of 120572POM (defined by (2)) in isothermal crystal-lization

claiming applicability of the single-crystal formula to nondi-lute systems More in general the depolarization ratio isnot proportional to crystallinity alone but to crystallinitymultiplied by a function of average plate dimensions [22]However assuming directly observable quantity 120572POM asa crystallization characteristic per se information aboutstructure formation (induction time) and structural changescan be obtained

33 Rheological Experiments In Figures 8(a) and 8(b) theevolution of the storage modulus (G1015840) the loss modulus (G10158401015840)and the complex viscosity (120578lowast) versus time during both thecooling (after the annealing process at 119879 = 120∘C) and theisothermal crystallization is reported together with the cor-responding temperature profiles for two different quiescentcrystallization tests

The experiment shows that both moduli (G1015840 and G10158401015840) aresusceptible to structural changes in the polymer As an exam-ple G1015840 after a first increase during the cooling step whichcan be ascribed to the effect of temperature shows a plateauat 119879 = 119879

119888 followed by a second increase representative of

The Scientific World Journal 5

0 1000 2000 3000 4000 5000 6000 7000Time (s)

40

55

70

85

100

115

130

Tem

pera

ture

(∘C)

1E+06

1E+05

1E+04

1E+03

1E+02

1E+01

1E+00

120578lowast

G998400998400G998400

T

G998400

(Pa)

G998400998400

(Pa)

120578lowast

(Palowast

s)

Tc = 45∘C

(a)

0 2000 4000 6000 8000 10000 12000Time (s)

40

55

70

85

100

115

130

Tem

pera

ture

(∘C)

1E+06

1E+05

1E+04

1E+03

1E+02

1E+01

1E+00

120578lowast

G998400998400G998400

T

G998400

(Pa)

G998400998400

(Pa)

120578lowast

(Palowast

s)

Tc = 47∘C

(b)

Figure 8 (a) Rheological measurements of the polycaprolactone crystallization at 45∘C storage modulus G1015840 loss modulus G10158401015840 complexviscosity 120578lowast and temperature measured simultaneously under constant stress of 100 Pa and constant frequency of 01 radsec (b) Rheologicalmeasurements of the polycaprolactone crystallization at 47∘C storage modulus G1015840 loss modulus G10158401015840 complex viscosity 120578lowast and temperaturemeasured simultaneously under constant stress of 100 Pa and constant frequency of 01 radsec

0

02

04

06

08

1

0 500 1000 1500 2000 2500 3000Isothermal time (s)

120572RH

EO(mdash

)

Tc = 45∘C

(a)

0

02

04

06

08

1

Isothermal time (s)0 1000 2000 3000 4000 5000 6000 7000 8000

120572RH

EO(mdash

)

Tc = 47∘C

(b)

Figure 9 (a) Comparison between rheological evolution and optical morphology during isothermal crystallization of PCL at 119879 = 45∘C (b)Comparison between rheological evolution and optical morphology during isothermal crystallization of PCL at 119879 = 47∘C

the crystallization process Finally a second plateau is foundwhen crystallinity reaches a maximum value

From the rheological experiment the induction time forthe isothermal crystallization can be detected at the timewhen the storage modulus abruptly increases The trans-formed crystallized fraction 120572RHEO(119905) has been estimatedfrom the time dependent 1198661015840(119905) values according to thefollowing equation [23]

120572RHEO (119905) =1198661015840

(119905) minus 1198661015840

0

1198661015840infin(119905) minus 119866

1015840

0

(3)

where 1198661015840119900 1198661015840(119905) and 1198661015840

infinare the melt stiffness values at time

0 119905 and infinity respectivelyThe results for the structure development during the

isothermal quiescent crystallization have been obtained atdifferent crystallization temperatures In Figures 9(a) and

9(b) the evolution of 120572RHEO to the isothermal crystallizationat 45∘C and 47∘C respectively is reported

The time scale starts at the end of the cooling step for boththe rheological and the morphological tests The times readfrom the figures are then directly related to the evolution ofthe crystallization in isothermal condition

The morphological investigation shows that spherulitesdevelop and growuntil the impingement occurs As expectedthe number of nuclei increases as the isothermal crystalliza-tion temperature decreases What is interesting is the com-parison between the structure development and the G1015840 trend(Figures 9(a) and 9(b)) Indeed in all the cases it hasbeen observed that spherulites appear and grow when thestorage modulus is still constant at the first plateau value(representative of G1015840 for the undercooled melt at 119879

119888) This

result is in agreement with the results reported by Aciernoet al [24] Bove and Nobile [25] and Pogodina et al [26]

6 The Scientific World Journal

100

75

50

25

00 25 50 75 100

t = 1300 s

(a)

100

75

50

25

00 25 50 75 100

t = 2000 s

(b)

100

75

50

25

00 25 50 75 100

t = 2500 s

(c)

100

75

50

25

00 25 50 75 100

t = 2900 s

(d)

100

75

50

25

00 25 50 75 100

t = 4100 s

(e)

Figure 10 AFM amplitude images on a square area with sides of 10120583m (119879119888= 50∘C)

The Scientific World Journal 7

The increase in G1015840 during time after the impingement is stillrelated to the crystallization process itself

34 AFM Experiments The same thermal protocol adoptedbefore was replicated during AFM measurements In thatcase however the recording of the data starts in parallelwith the second cooling step (T lt 60∘C) In contrast to thatobserved with the calorimetric experiments the first signalof structures formation was observed during the secondcooling step at temperatures just below 50∘C For that it wasimpossible to carry out isothermal AFM tests at temperaturelower than 50∘C

The evolution of the samples surface morphology wasrecoded in terms of distance from a reference position(height) and the characteristic oscillation (amplitude andphase) of the AFM cantilever during the observation timesThe three acquired signals are strictly related to the structureformation on the sample surface during the crystallizationphenomena However in our case the amplitude signal wasfound themost sensible to the change in surfacemorphology

For the present analysis two different tests were consid-ered one with an observed square area with a side of 10 120583mand another withwider area having a side of 30 120583mAs shownin Figure 10 some evidence of crystalline structures appearson the surface after about 1500 s in isothermal conditions

The crystalline structure development was followed byAFM while growing and it was found that the growth frontpropagates by the advancement of primary arms with theregions between the arms filled in by secondary arms growingbehind the primary front [27]

During the isothermal step new crystal aggregates werenot formed but just the development of the previously formedstructures was evident This observation is coherent with thehypothesis of nucleation dependence on temperature andthus during the isothermal step no new stable nuclei areformed

The development of new crystalline structures on thesample surface was followed by means of the evolution of theaverage value of the amplitude signal 119860(119905) during the wholetest

In particular by assuming as initial value of the averagedamplitude (119860

0) the value that 119860(119905) assumes at starting crys-

tallization time the variations of the averaged amplitude foreach time (119860(119905) minus119860

0) divided by the total variation recorded

during the whole test can be transformed into a variationindex (120572AFM(119905))

120572AFM (119905) =int119905

0

(119860 (119905) minus 1198600) 119889119905

intinfin

0

(119860 (119905) minus 1198600) 119889119905

(4)

In Figure 11 is reported for both tests conditions the evo-lution of 120572AFM(119905) as function of the isothermal crystallizationtime

At early stage of the crystallization process a small part ofthe investigated surface is covered by crystalline structure sothe variations of the averaged amplitude signal are very lowAs the crystallization proceeds the variations of the averagedamplitude become larger until a large part of the surface is

0

20

40

60

80

100

0 2000 4000 6000 8000 10000 12000Isothermal time (s)

120572A

FM(mdash

) (

)

10120583m30120583m

Figure 11 Evolution of averaged amplitude of AFM test on a squarearea with sides of 10120583m and 30 120583m

covered by the crystalline structure and therefore the varia-tions of the averaged amplitude are constant

As expected even on the same sample the morphologyappears very different by changing the surface analyzed Thisis clearly shown in Figure 12 where the same sample shows adifferent texture by changing the scanned area

4 Discussions

All the techniques adopted in this work were analysed insuch a way to obtain sigmoidal curves representative of theevolution of the crystallization From all the curves it waspossible to identify an induction time as the time at which themeasured signal deviates from the value that it presents at thestart of the isothermal step when the sample is still moltenwithout any crystallinity A comparison between the resultsobtained with the different techniques presented is shown inFigure 13

Results clearly reveal that the induction time found on theentire range of crystallization is dependent on the techniqueused As expected the observation scale plays an importantrole in its determination Rheology appears to be the leastsensitive technique probably because in order to measurean increase in rheological parameters an interaction amongcrystals is necessary On the contrary AFM tests that are ableto resolve the surface sample at dimensions comparable to theprimary nuclei can detect crystallization at initial stages

5 Conclusions

The morphological development taking place during thecrystallization of polycaprolactone (PCL) was studied usingseveral techniques

Results show that the induction time is dependent on thetechnique used As expected the observation scale plays animportant role in its determination In particular despite itslimitations the AFM that is able to resolve the surface sampleat dimensions comparable to the primary nuclei is able

8 The Scientific World Journal

100

75

50

25

00 25 50 75 100

(120583m)

(a)

300

200

100

00 100 200 300

(120583m)

(b)

Figure 12 AFM amplitude images on different areas after complete crystallization

10

100

1000

10000

41 42 43 44 45 46 47 48 49 50 51

Indu

ctio

n tim

e (s)

DSCPOMRheology

Temperature (∘C)

AFM 10120583mAFM 30120583m

Figure 13 Induction time recorder by the different techniques Thedashed line represents a guide for eyes

to detect crystallization at initial stages On the contraryrheology appears to be the least sensitive technique probablybecause in order to measure an increase in rheologicalparameters an interaction among crystals is necessary DSCand POM techniques supply closer results It suggests that thedefinition of induction time in the polymer crystallization isa vague concept that in any case requires the definition ofthe technique used for its characterization

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] R Pantani I Coccorullo V Speranza and G TitomanlioldquoModeling of morphology evolution in the injection moldingprocess of thermoplastic polymersrdquo Progress in Polymer Sciencevol 30 no 12 pp 1185ndash1222 2005

[2] R Pantani V Speranza A Sorrentino and G TitomanlioldquoMolecular orientation and strain in injectionmoulding of ther-moplasticsrdquo Macromolecular Symposia vol 185 no 1 pp 293ndash307 2002

[3] R Pearce and G J Vancso ldquoImaging of melting and crystalliza-tion of poly(ethylene oxide) in real-time by hot-stage atomicforce microscopyrdquo Macromolecules vol 30 no 19 pp 5843ndash5848 1997

[4] R Pearce and G J Vancso ldquoReal-time imaging of meltingand crystallization in poly(ethylene oxide) by atomic forcemicroscopyrdquo Polymer vol 39 no 5 pp 1237ndash1242 1998

[5] R Pearce and G J Vancso ldquoObservations of crystallizationandmelting in poly(ethylene oxide)poly(methyl methacrylate)blends by hot-stage atomic-force microscopyrdquo Journal of Poly-mer Science B vol 36 no 14 pp 2643ndash2651 1998

[6] J M Schultz and M J Miles ldquoAFM study of morphologicaldevelopment during the melt-crystallization of poly(ethyleneoxide)rdquo Journal of Polymer Science B vol 36 no 13 pp 2311ndash2325 1998

[7] T J McMaster J K Hobbs P J Barham and M J Miles ldquoAFMstudy of in situ real time polymer crystallization and spherulitestructurerdquo Probe Microscopy vol 1 no 1 pp 43ndash56 1997

[8] L Li C-M Chan K L Yeung J-X Li K-M Ng and Y LeildquoDirect observation of growth of lamellae and spherulites of asemicrystalline polymer by AFMrdquoMacromolecules vol 34 no2 pp 316ndash325 2001

[9] J K Hobbs T JMcMasterM JMiles and P J Barham ldquoDirectobservations of the growth of spherulites of poly(hydrox-ybutyrate-co-valerate) using atomic force microscopyrdquo Poly-mer vol 39 no 12 pp 2437ndash2446 1998

The Scientific World Journal 9

[10] L G M Beekmans R Valle and G J Vancso ldquoNucleation andgrowth of poly(120576-caprolactone) on poly(tetrafluoroethylene) byin-situ AFMrdquo Macromolecules vol 35 no 25 pp 9383ndash93902002

[11] W Zhou S Z D Cheng S Putthanarat et al ldquoCrystallizationmelting and morphology of syndiotactic polypropylene frac-tions 4 In situ lamellar single crystal growth and melting indifferent sectorsrdquoMacromolecules vol 33 no 18 pp 6861ndash68682000

[12] Y Jiang D-D Yan X Gao et al ldquoLamellar branching ofpoly(bisphenol A-co-decane) spherulites at different tempera-tures studied by high-temperature AFMrdquo Macromolecules vol36 no 10 pp 3652ndash3655 2003

[13] D A Ivanov Z Amalou and S N Magonov ldquoReal-time evolu-tion of the lamellar organization of poly(ethylene terephthalate)during crystallization from the melt high-temperature atomicforce microscopy studyrdquo Macromolecules vol 34 no 26 pp8944ndash8952 2001

[14] Y Kikkawa H Abe M Fujita T Iwata Y Inoue and Y DoildquoCrystal growth in poly(l-lactide) thin film revealed by insitu atomic force microscopyrdquo Macromolecular Chemistry andPhysics vol 204 no 15 pp 1822ndash1831 2003

[15] R Pantani V Speranza and G Titomanlio ldquoRelevance of crys-tallisation kinetics in the simulation of the injection moldingprocessrdquo International Polymer Processing vol 16 no 1 pp 61ndash71 2001

[16] A Martins W Zhang M Brito U Infante M Romero andF O Soares ldquoIsothermal and nonisothermal crystallization ofpolymers analysis with a shear differential thermal analyzerrdquoReview of Scientific Instruments vol 76 no 10 Article ID 1051052005

[17] W Nagatake T Takahashi Y Masubuchi J-I Takimoto andK Koyama ldquoDevelopment of shear flow thermal rheometer fordirect measurement of crystallization fraction of polymer meltsunder shear deformationrdquo Polymer vol 41 no 2 pp 523ndash5312000

[18] F de Santis A R Vietri and R Pantani ldquoMorphology evolutionduring polymer crystallization simultaneous calorimetric andoptical measurementsrdquoMacromolecular Symposia vol 234 pp7ndash12 2006

[19] A Sorrentino R Pantani and G Titomanlio ldquoKinetics ofmelting and characterization of the thermodynamic and kineticproperties of syndiotactic polystyrenerdquo Journal of PolymerScience B vol 45 no 2 pp 196ndash207 2007

[20] A Ziabicki ldquoApplicability of light transmission technique tostudies of crystalline polymers texturerdquo Kolloid-Zeitschrift ampZeitschrift fur Polymere vol 219 no 1 pp 2ndash12 1967

[21] F L Binsbergen ldquoDepolarization of linearly polarized light bya polycrystalline specimenrdquo Journal of Macromolecular ScienceB vol 4 pp 837ndash851 1970

[22] A Ziabicki and B Misztal-Faraj ldquoApplicability of light depolar-ization technique to crystallization studiesrdquoPolymer vol 46 no7 pp 2395ndash2403 2005

[23] Y P Khanna ldquoRheological mechanism and overview of nucle-ated crystallization kineticsrdquoMacromolecules vol 26 no 14 pp3639ndash3643 1993

[24] S Acierno E di Maio S Iannace and N Grizzuti ldquoStructuredevelopment during crystallization of polycaprolactonerdquo Rheo-logica Acta vol 45 no 4 pp 387ndash392 2006

[25] L Bove and M R Nobile ldquoShear-induced crystallization ofisotactic poly(1-butene)rdquoMacromolecular Symposia vol 185 no1 pp 135ndash147 2002

[26] N V Pogodina V P Lavrenko S Srinivas and H H WinterldquoRheology and structure of isotactic polypropylene near thegel point quiescent and shear-induced crystallizationrdquoPolymervol 42 no 21 pp 9031ndash9043 2001

[27] L G M Beekmans and G J Vancso ldquoReal-time crystalliza-tion study of poly(120576-caprolactone) by hot-stage atomic forcemicroscopyrdquo Polymer vol 41 no 25 pp 8975ndash8981 2000

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Page 5: Research Article Characterization of the Polycaprolactone ...downloads.hindawi.com/journals/tswj/2014/720157.pdfe application of atomic force microscopy (AFM) to polymer system is

The Scientific World Journal 5

0 1000 2000 3000 4000 5000 6000 7000Time (s)

40

55

70

85

100

115

130

Tem

pera

ture

(∘C)

1E+06

1E+05

1E+04

1E+03

1E+02

1E+01

1E+00

120578lowast

G998400998400G998400

T

G998400

(Pa)

G998400998400

(Pa)

120578lowast

(Palowast

s)

Tc = 45∘C

(a)

0 2000 4000 6000 8000 10000 12000Time (s)

40

55

70

85

100

115

130

Tem

pera

ture

(∘C)

1E+06

1E+05

1E+04

1E+03

1E+02

1E+01

1E+00

120578lowast

G998400998400G998400

T

G998400

(Pa)

G998400998400

(Pa)

120578lowast

(Palowast

s)

Tc = 47∘C

(b)

Figure 8 (a) Rheological measurements of the polycaprolactone crystallization at 45∘C storage modulus G1015840 loss modulus G10158401015840 complexviscosity 120578lowast and temperature measured simultaneously under constant stress of 100 Pa and constant frequency of 01 radsec (b) Rheologicalmeasurements of the polycaprolactone crystallization at 47∘C storage modulus G1015840 loss modulus G10158401015840 complex viscosity 120578lowast and temperaturemeasured simultaneously under constant stress of 100 Pa and constant frequency of 01 radsec

0

02

04

06

08

1

0 500 1000 1500 2000 2500 3000Isothermal time (s)

120572RH

EO(mdash

)

Tc = 45∘C

(a)

0

02

04

06

08

1

Isothermal time (s)0 1000 2000 3000 4000 5000 6000 7000 8000

120572RH

EO(mdash

)

Tc = 47∘C

(b)

Figure 9 (a) Comparison between rheological evolution and optical morphology during isothermal crystallization of PCL at 119879 = 45∘C (b)Comparison between rheological evolution and optical morphology during isothermal crystallization of PCL at 119879 = 47∘C

the crystallization process Finally a second plateau is foundwhen crystallinity reaches a maximum value

From the rheological experiment the induction time forthe isothermal crystallization can be detected at the timewhen the storage modulus abruptly increases The trans-formed crystallized fraction 120572RHEO(119905) has been estimatedfrom the time dependent 1198661015840(119905) values according to thefollowing equation [23]

120572RHEO (119905) =1198661015840

(119905) minus 1198661015840

0

1198661015840infin(119905) minus 119866

1015840

0

(3)

where 1198661015840119900 1198661015840(119905) and 1198661015840

infinare the melt stiffness values at time

0 119905 and infinity respectivelyThe results for the structure development during the

isothermal quiescent crystallization have been obtained atdifferent crystallization temperatures In Figures 9(a) and

9(b) the evolution of 120572RHEO to the isothermal crystallizationat 45∘C and 47∘C respectively is reported

The time scale starts at the end of the cooling step for boththe rheological and the morphological tests The times readfrom the figures are then directly related to the evolution ofthe crystallization in isothermal condition

The morphological investigation shows that spherulitesdevelop and growuntil the impingement occurs As expectedthe number of nuclei increases as the isothermal crystalliza-tion temperature decreases What is interesting is the com-parison between the structure development and the G1015840 trend(Figures 9(a) and 9(b)) Indeed in all the cases it hasbeen observed that spherulites appear and grow when thestorage modulus is still constant at the first plateau value(representative of G1015840 for the undercooled melt at 119879

119888) This

result is in agreement with the results reported by Aciernoet al [24] Bove and Nobile [25] and Pogodina et al [26]

6 The Scientific World Journal

100

75

50

25

00 25 50 75 100

t = 1300 s

(a)

100

75

50

25

00 25 50 75 100

t = 2000 s

(b)

100

75

50

25

00 25 50 75 100

t = 2500 s

(c)

100

75

50

25

00 25 50 75 100

t = 2900 s

(d)

100

75

50

25

00 25 50 75 100

t = 4100 s

(e)

Figure 10 AFM amplitude images on a square area with sides of 10120583m (119879119888= 50∘C)

The Scientific World Journal 7

The increase in G1015840 during time after the impingement is stillrelated to the crystallization process itself

34 AFM Experiments The same thermal protocol adoptedbefore was replicated during AFM measurements In thatcase however the recording of the data starts in parallelwith the second cooling step (T lt 60∘C) In contrast to thatobserved with the calorimetric experiments the first signalof structures formation was observed during the secondcooling step at temperatures just below 50∘C For that it wasimpossible to carry out isothermal AFM tests at temperaturelower than 50∘C

The evolution of the samples surface morphology wasrecoded in terms of distance from a reference position(height) and the characteristic oscillation (amplitude andphase) of the AFM cantilever during the observation timesThe three acquired signals are strictly related to the structureformation on the sample surface during the crystallizationphenomena However in our case the amplitude signal wasfound themost sensible to the change in surfacemorphology

For the present analysis two different tests were consid-ered one with an observed square area with a side of 10 120583mand another withwider area having a side of 30 120583mAs shownin Figure 10 some evidence of crystalline structures appearson the surface after about 1500 s in isothermal conditions

The crystalline structure development was followed byAFM while growing and it was found that the growth frontpropagates by the advancement of primary arms with theregions between the arms filled in by secondary arms growingbehind the primary front [27]

During the isothermal step new crystal aggregates werenot formed but just the development of the previously formedstructures was evident This observation is coherent with thehypothesis of nucleation dependence on temperature andthus during the isothermal step no new stable nuclei areformed

The development of new crystalline structures on thesample surface was followed by means of the evolution of theaverage value of the amplitude signal 119860(119905) during the wholetest

In particular by assuming as initial value of the averagedamplitude (119860

0) the value that 119860(119905) assumes at starting crys-

tallization time the variations of the averaged amplitude foreach time (119860(119905) minus119860

0) divided by the total variation recorded

during the whole test can be transformed into a variationindex (120572AFM(119905))

120572AFM (119905) =int119905

0

(119860 (119905) minus 1198600) 119889119905

intinfin

0

(119860 (119905) minus 1198600) 119889119905

(4)

In Figure 11 is reported for both tests conditions the evo-lution of 120572AFM(119905) as function of the isothermal crystallizationtime

At early stage of the crystallization process a small part ofthe investigated surface is covered by crystalline structure sothe variations of the averaged amplitude signal are very lowAs the crystallization proceeds the variations of the averagedamplitude become larger until a large part of the surface is

0

20

40

60

80

100

0 2000 4000 6000 8000 10000 12000Isothermal time (s)

120572A

FM(mdash

) (

)

10120583m30120583m

Figure 11 Evolution of averaged amplitude of AFM test on a squarearea with sides of 10120583m and 30 120583m

covered by the crystalline structure and therefore the varia-tions of the averaged amplitude are constant

As expected even on the same sample the morphologyappears very different by changing the surface analyzed Thisis clearly shown in Figure 12 where the same sample shows adifferent texture by changing the scanned area

4 Discussions

All the techniques adopted in this work were analysed insuch a way to obtain sigmoidal curves representative of theevolution of the crystallization From all the curves it waspossible to identify an induction time as the time at which themeasured signal deviates from the value that it presents at thestart of the isothermal step when the sample is still moltenwithout any crystallinity A comparison between the resultsobtained with the different techniques presented is shown inFigure 13

Results clearly reveal that the induction time found on theentire range of crystallization is dependent on the techniqueused As expected the observation scale plays an importantrole in its determination Rheology appears to be the leastsensitive technique probably because in order to measurean increase in rheological parameters an interaction amongcrystals is necessary On the contrary AFM tests that are ableto resolve the surface sample at dimensions comparable to theprimary nuclei can detect crystallization at initial stages

5 Conclusions

The morphological development taking place during thecrystallization of polycaprolactone (PCL) was studied usingseveral techniques

Results show that the induction time is dependent on thetechnique used As expected the observation scale plays animportant role in its determination In particular despite itslimitations the AFM that is able to resolve the surface sampleat dimensions comparable to the primary nuclei is able

8 The Scientific World Journal

100

75

50

25

00 25 50 75 100

(120583m)

(a)

300

200

100

00 100 200 300

(120583m)

(b)

Figure 12 AFM amplitude images on different areas after complete crystallization

10

100

1000

10000

41 42 43 44 45 46 47 48 49 50 51

Indu

ctio

n tim

e (s)

DSCPOMRheology

Temperature (∘C)

AFM 10120583mAFM 30120583m

Figure 13 Induction time recorder by the different techniques Thedashed line represents a guide for eyes

to detect crystallization at initial stages On the contraryrheology appears to be the least sensitive technique probablybecause in order to measure an increase in rheologicalparameters an interaction among crystals is necessary DSCand POM techniques supply closer results It suggests that thedefinition of induction time in the polymer crystallization isa vague concept that in any case requires the definition ofthe technique used for its characterization

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] R Pantani I Coccorullo V Speranza and G TitomanlioldquoModeling of morphology evolution in the injection moldingprocess of thermoplastic polymersrdquo Progress in Polymer Sciencevol 30 no 12 pp 1185ndash1222 2005

[2] R Pantani V Speranza A Sorrentino and G TitomanlioldquoMolecular orientation and strain in injectionmoulding of ther-moplasticsrdquo Macromolecular Symposia vol 185 no 1 pp 293ndash307 2002

[3] R Pearce and G J Vancso ldquoImaging of melting and crystalliza-tion of poly(ethylene oxide) in real-time by hot-stage atomicforce microscopyrdquo Macromolecules vol 30 no 19 pp 5843ndash5848 1997

[4] R Pearce and G J Vancso ldquoReal-time imaging of meltingand crystallization in poly(ethylene oxide) by atomic forcemicroscopyrdquo Polymer vol 39 no 5 pp 1237ndash1242 1998

[5] R Pearce and G J Vancso ldquoObservations of crystallizationandmelting in poly(ethylene oxide)poly(methyl methacrylate)blends by hot-stage atomic-force microscopyrdquo Journal of Poly-mer Science B vol 36 no 14 pp 2643ndash2651 1998

[6] J M Schultz and M J Miles ldquoAFM study of morphologicaldevelopment during the melt-crystallization of poly(ethyleneoxide)rdquo Journal of Polymer Science B vol 36 no 13 pp 2311ndash2325 1998

[7] T J McMaster J K Hobbs P J Barham and M J Miles ldquoAFMstudy of in situ real time polymer crystallization and spherulitestructurerdquo Probe Microscopy vol 1 no 1 pp 43ndash56 1997

[8] L Li C-M Chan K L Yeung J-X Li K-M Ng and Y LeildquoDirect observation of growth of lamellae and spherulites of asemicrystalline polymer by AFMrdquoMacromolecules vol 34 no2 pp 316ndash325 2001

[9] J K Hobbs T JMcMasterM JMiles and P J Barham ldquoDirectobservations of the growth of spherulites of poly(hydrox-ybutyrate-co-valerate) using atomic force microscopyrdquo Poly-mer vol 39 no 12 pp 2437ndash2446 1998

The Scientific World Journal 9

[10] L G M Beekmans R Valle and G J Vancso ldquoNucleation andgrowth of poly(120576-caprolactone) on poly(tetrafluoroethylene) byin-situ AFMrdquo Macromolecules vol 35 no 25 pp 9383ndash93902002

[11] W Zhou S Z D Cheng S Putthanarat et al ldquoCrystallizationmelting and morphology of syndiotactic polypropylene frac-tions 4 In situ lamellar single crystal growth and melting indifferent sectorsrdquoMacromolecules vol 33 no 18 pp 6861ndash68682000

[12] Y Jiang D-D Yan X Gao et al ldquoLamellar branching ofpoly(bisphenol A-co-decane) spherulites at different tempera-tures studied by high-temperature AFMrdquo Macromolecules vol36 no 10 pp 3652ndash3655 2003

[13] D A Ivanov Z Amalou and S N Magonov ldquoReal-time evolu-tion of the lamellar organization of poly(ethylene terephthalate)during crystallization from the melt high-temperature atomicforce microscopy studyrdquo Macromolecules vol 34 no 26 pp8944ndash8952 2001

[14] Y Kikkawa H Abe M Fujita T Iwata Y Inoue and Y DoildquoCrystal growth in poly(l-lactide) thin film revealed by insitu atomic force microscopyrdquo Macromolecular Chemistry andPhysics vol 204 no 15 pp 1822ndash1831 2003

[15] R Pantani V Speranza and G Titomanlio ldquoRelevance of crys-tallisation kinetics in the simulation of the injection moldingprocessrdquo International Polymer Processing vol 16 no 1 pp 61ndash71 2001

[16] A Martins W Zhang M Brito U Infante M Romero andF O Soares ldquoIsothermal and nonisothermal crystallization ofpolymers analysis with a shear differential thermal analyzerrdquoReview of Scientific Instruments vol 76 no 10 Article ID 1051052005

[17] W Nagatake T Takahashi Y Masubuchi J-I Takimoto andK Koyama ldquoDevelopment of shear flow thermal rheometer fordirect measurement of crystallization fraction of polymer meltsunder shear deformationrdquo Polymer vol 41 no 2 pp 523ndash5312000

[18] F de Santis A R Vietri and R Pantani ldquoMorphology evolutionduring polymer crystallization simultaneous calorimetric andoptical measurementsrdquoMacromolecular Symposia vol 234 pp7ndash12 2006

[19] A Sorrentino R Pantani and G Titomanlio ldquoKinetics ofmelting and characterization of the thermodynamic and kineticproperties of syndiotactic polystyrenerdquo Journal of PolymerScience B vol 45 no 2 pp 196ndash207 2007

[20] A Ziabicki ldquoApplicability of light transmission technique tostudies of crystalline polymers texturerdquo Kolloid-Zeitschrift ampZeitschrift fur Polymere vol 219 no 1 pp 2ndash12 1967

[21] F L Binsbergen ldquoDepolarization of linearly polarized light bya polycrystalline specimenrdquo Journal of Macromolecular ScienceB vol 4 pp 837ndash851 1970

[22] A Ziabicki and B Misztal-Faraj ldquoApplicability of light depolar-ization technique to crystallization studiesrdquoPolymer vol 46 no7 pp 2395ndash2403 2005

[23] Y P Khanna ldquoRheological mechanism and overview of nucle-ated crystallization kineticsrdquoMacromolecules vol 26 no 14 pp3639ndash3643 1993

[24] S Acierno E di Maio S Iannace and N Grizzuti ldquoStructuredevelopment during crystallization of polycaprolactonerdquo Rheo-logica Acta vol 45 no 4 pp 387ndash392 2006

[25] L Bove and M R Nobile ldquoShear-induced crystallization ofisotactic poly(1-butene)rdquoMacromolecular Symposia vol 185 no1 pp 135ndash147 2002

[26] N V Pogodina V P Lavrenko S Srinivas and H H WinterldquoRheology and structure of isotactic polypropylene near thegel point quiescent and shear-induced crystallizationrdquoPolymervol 42 no 21 pp 9031ndash9043 2001

[27] L G M Beekmans and G J Vancso ldquoReal-time crystalliza-tion study of poly(120576-caprolactone) by hot-stage atomic forcemicroscopyrdquo Polymer vol 41 no 25 pp 8975ndash8981 2000

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Page 6: Research Article Characterization of the Polycaprolactone ...downloads.hindawi.com/journals/tswj/2014/720157.pdfe application of atomic force microscopy (AFM) to polymer system is

6 The Scientific World Journal

100

75

50

25

00 25 50 75 100

t = 1300 s

(a)

100

75

50

25

00 25 50 75 100

t = 2000 s

(b)

100

75

50

25

00 25 50 75 100

t = 2500 s

(c)

100

75

50

25

00 25 50 75 100

t = 2900 s

(d)

100

75

50

25

00 25 50 75 100

t = 4100 s

(e)

Figure 10 AFM amplitude images on a square area with sides of 10120583m (119879119888= 50∘C)

The Scientific World Journal 7

The increase in G1015840 during time after the impingement is stillrelated to the crystallization process itself

34 AFM Experiments The same thermal protocol adoptedbefore was replicated during AFM measurements In thatcase however the recording of the data starts in parallelwith the second cooling step (T lt 60∘C) In contrast to thatobserved with the calorimetric experiments the first signalof structures formation was observed during the secondcooling step at temperatures just below 50∘C For that it wasimpossible to carry out isothermal AFM tests at temperaturelower than 50∘C

The evolution of the samples surface morphology wasrecoded in terms of distance from a reference position(height) and the characteristic oscillation (amplitude andphase) of the AFM cantilever during the observation timesThe three acquired signals are strictly related to the structureformation on the sample surface during the crystallizationphenomena However in our case the amplitude signal wasfound themost sensible to the change in surfacemorphology

For the present analysis two different tests were consid-ered one with an observed square area with a side of 10 120583mand another withwider area having a side of 30 120583mAs shownin Figure 10 some evidence of crystalline structures appearson the surface after about 1500 s in isothermal conditions

The crystalline structure development was followed byAFM while growing and it was found that the growth frontpropagates by the advancement of primary arms with theregions between the arms filled in by secondary arms growingbehind the primary front [27]

During the isothermal step new crystal aggregates werenot formed but just the development of the previously formedstructures was evident This observation is coherent with thehypothesis of nucleation dependence on temperature andthus during the isothermal step no new stable nuclei areformed

The development of new crystalline structures on thesample surface was followed by means of the evolution of theaverage value of the amplitude signal 119860(119905) during the wholetest

In particular by assuming as initial value of the averagedamplitude (119860

0) the value that 119860(119905) assumes at starting crys-

tallization time the variations of the averaged amplitude foreach time (119860(119905) minus119860

0) divided by the total variation recorded

during the whole test can be transformed into a variationindex (120572AFM(119905))

120572AFM (119905) =int119905

0

(119860 (119905) minus 1198600) 119889119905

intinfin

0

(119860 (119905) minus 1198600) 119889119905

(4)

In Figure 11 is reported for both tests conditions the evo-lution of 120572AFM(119905) as function of the isothermal crystallizationtime

At early stage of the crystallization process a small part ofthe investigated surface is covered by crystalline structure sothe variations of the averaged amplitude signal are very lowAs the crystallization proceeds the variations of the averagedamplitude become larger until a large part of the surface is

0

20

40

60

80

100

0 2000 4000 6000 8000 10000 12000Isothermal time (s)

120572A

FM(mdash

) (

)

10120583m30120583m

Figure 11 Evolution of averaged amplitude of AFM test on a squarearea with sides of 10120583m and 30 120583m

covered by the crystalline structure and therefore the varia-tions of the averaged amplitude are constant

As expected even on the same sample the morphologyappears very different by changing the surface analyzed Thisis clearly shown in Figure 12 where the same sample shows adifferent texture by changing the scanned area

4 Discussions

All the techniques adopted in this work were analysed insuch a way to obtain sigmoidal curves representative of theevolution of the crystallization From all the curves it waspossible to identify an induction time as the time at which themeasured signal deviates from the value that it presents at thestart of the isothermal step when the sample is still moltenwithout any crystallinity A comparison between the resultsobtained with the different techniques presented is shown inFigure 13

Results clearly reveal that the induction time found on theentire range of crystallization is dependent on the techniqueused As expected the observation scale plays an importantrole in its determination Rheology appears to be the leastsensitive technique probably because in order to measurean increase in rheological parameters an interaction amongcrystals is necessary On the contrary AFM tests that are ableto resolve the surface sample at dimensions comparable to theprimary nuclei can detect crystallization at initial stages

5 Conclusions

The morphological development taking place during thecrystallization of polycaprolactone (PCL) was studied usingseveral techniques

Results show that the induction time is dependent on thetechnique used As expected the observation scale plays animportant role in its determination In particular despite itslimitations the AFM that is able to resolve the surface sampleat dimensions comparable to the primary nuclei is able

8 The Scientific World Journal

100

75

50

25

00 25 50 75 100

(120583m)

(a)

300

200

100

00 100 200 300

(120583m)

(b)

Figure 12 AFM amplitude images on different areas after complete crystallization

10

100

1000

10000

41 42 43 44 45 46 47 48 49 50 51

Indu

ctio

n tim

e (s)

DSCPOMRheology

Temperature (∘C)

AFM 10120583mAFM 30120583m

Figure 13 Induction time recorder by the different techniques Thedashed line represents a guide for eyes

to detect crystallization at initial stages On the contraryrheology appears to be the least sensitive technique probablybecause in order to measure an increase in rheologicalparameters an interaction among crystals is necessary DSCand POM techniques supply closer results It suggests that thedefinition of induction time in the polymer crystallization isa vague concept that in any case requires the definition ofthe technique used for its characterization

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] R Pantani I Coccorullo V Speranza and G TitomanlioldquoModeling of morphology evolution in the injection moldingprocess of thermoplastic polymersrdquo Progress in Polymer Sciencevol 30 no 12 pp 1185ndash1222 2005

[2] R Pantani V Speranza A Sorrentino and G TitomanlioldquoMolecular orientation and strain in injectionmoulding of ther-moplasticsrdquo Macromolecular Symposia vol 185 no 1 pp 293ndash307 2002

[3] R Pearce and G J Vancso ldquoImaging of melting and crystalliza-tion of poly(ethylene oxide) in real-time by hot-stage atomicforce microscopyrdquo Macromolecules vol 30 no 19 pp 5843ndash5848 1997

[4] R Pearce and G J Vancso ldquoReal-time imaging of meltingand crystallization in poly(ethylene oxide) by atomic forcemicroscopyrdquo Polymer vol 39 no 5 pp 1237ndash1242 1998

[5] R Pearce and G J Vancso ldquoObservations of crystallizationandmelting in poly(ethylene oxide)poly(methyl methacrylate)blends by hot-stage atomic-force microscopyrdquo Journal of Poly-mer Science B vol 36 no 14 pp 2643ndash2651 1998

[6] J M Schultz and M J Miles ldquoAFM study of morphologicaldevelopment during the melt-crystallization of poly(ethyleneoxide)rdquo Journal of Polymer Science B vol 36 no 13 pp 2311ndash2325 1998

[7] T J McMaster J K Hobbs P J Barham and M J Miles ldquoAFMstudy of in situ real time polymer crystallization and spherulitestructurerdquo Probe Microscopy vol 1 no 1 pp 43ndash56 1997

[8] L Li C-M Chan K L Yeung J-X Li K-M Ng and Y LeildquoDirect observation of growth of lamellae and spherulites of asemicrystalline polymer by AFMrdquoMacromolecules vol 34 no2 pp 316ndash325 2001

[9] J K Hobbs T JMcMasterM JMiles and P J Barham ldquoDirectobservations of the growth of spherulites of poly(hydrox-ybutyrate-co-valerate) using atomic force microscopyrdquo Poly-mer vol 39 no 12 pp 2437ndash2446 1998

The Scientific World Journal 9

[10] L G M Beekmans R Valle and G J Vancso ldquoNucleation andgrowth of poly(120576-caprolactone) on poly(tetrafluoroethylene) byin-situ AFMrdquo Macromolecules vol 35 no 25 pp 9383ndash93902002

[11] W Zhou S Z D Cheng S Putthanarat et al ldquoCrystallizationmelting and morphology of syndiotactic polypropylene frac-tions 4 In situ lamellar single crystal growth and melting indifferent sectorsrdquoMacromolecules vol 33 no 18 pp 6861ndash68682000

[12] Y Jiang D-D Yan X Gao et al ldquoLamellar branching ofpoly(bisphenol A-co-decane) spherulites at different tempera-tures studied by high-temperature AFMrdquo Macromolecules vol36 no 10 pp 3652ndash3655 2003

[13] D A Ivanov Z Amalou and S N Magonov ldquoReal-time evolu-tion of the lamellar organization of poly(ethylene terephthalate)during crystallization from the melt high-temperature atomicforce microscopy studyrdquo Macromolecules vol 34 no 26 pp8944ndash8952 2001

[14] Y Kikkawa H Abe M Fujita T Iwata Y Inoue and Y DoildquoCrystal growth in poly(l-lactide) thin film revealed by insitu atomic force microscopyrdquo Macromolecular Chemistry andPhysics vol 204 no 15 pp 1822ndash1831 2003

[15] R Pantani V Speranza and G Titomanlio ldquoRelevance of crys-tallisation kinetics in the simulation of the injection moldingprocessrdquo International Polymer Processing vol 16 no 1 pp 61ndash71 2001

[16] A Martins W Zhang M Brito U Infante M Romero andF O Soares ldquoIsothermal and nonisothermal crystallization ofpolymers analysis with a shear differential thermal analyzerrdquoReview of Scientific Instruments vol 76 no 10 Article ID 1051052005

[17] W Nagatake T Takahashi Y Masubuchi J-I Takimoto andK Koyama ldquoDevelopment of shear flow thermal rheometer fordirect measurement of crystallization fraction of polymer meltsunder shear deformationrdquo Polymer vol 41 no 2 pp 523ndash5312000

[18] F de Santis A R Vietri and R Pantani ldquoMorphology evolutionduring polymer crystallization simultaneous calorimetric andoptical measurementsrdquoMacromolecular Symposia vol 234 pp7ndash12 2006

[19] A Sorrentino R Pantani and G Titomanlio ldquoKinetics ofmelting and characterization of the thermodynamic and kineticproperties of syndiotactic polystyrenerdquo Journal of PolymerScience B vol 45 no 2 pp 196ndash207 2007

[20] A Ziabicki ldquoApplicability of light transmission technique tostudies of crystalline polymers texturerdquo Kolloid-Zeitschrift ampZeitschrift fur Polymere vol 219 no 1 pp 2ndash12 1967

[21] F L Binsbergen ldquoDepolarization of linearly polarized light bya polycrystalline specimenrdquo Journal of Macromolecular ScienceB vol 4 pp 837ndash851 1970

[22] A Ziabicki and B Misztal-Faraj ldquoApplicability of light depolar-ization technique to crystallization studiesrdquoPolymer vol 46 no7 pp 2395ndash2403 2005

[23] Y P Khanna ldquoRheological mechanism and overview of nucle-ated crystallization kineticsrdquoMacromolecules vol 26 no 14 pp3639ndash3643 1993

[24] S Acierno E di Maio S Iannace and N Grizzuti ldquoStructuredevelopment during crystallization of polycaprolactonerdquo Rheo-logica Acta vol 45 no 4 pp 387ndash392 2006

[25] L Bove and M R Nobile ldquoShear-induced crystallization ofisotactic poly(1-butene)rdquoMacromolecular Symposia vol 185 no1 pp 135ndash147 2002

[26] N V Pogodina V P Lavrenko S Srinivas and H H WinterldquoRheology and structure of isotactic polypropylene near thegel point quiescent and shear-induced crystallizationrdquoPolymervol 42 no 21 pp 9031ndash9043 2001

[27] L G M Beekmans and G J Vancso ldquoReal-time crystalliza-tion study of poly(120576-caprolactone) by hot-stage atomic forcemicroscopyrdquo Polymer vol 41 no 25 pp 8975ndash8981 2000

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Page 7: Research Article Characterization of the Polycaprolactone ...downloads.hindawi.com/journals/tswj/2014/720157.pdfe application of atomic force microscopy (AFM) to polymer system is

The Scientific World Journal 7

The increase in G1015840 during time after the impingement is stillrelated to the crystallization process itself

34 AFM Experiments The same thermal protocol adoptedbefore was replicated during AFM measurements In thatcase however the recording of the data starts in parallelwith the second cooling step (T lt 60∘C) In contrast to thatobserved with the calorimetric experiments the first signalof structures formation was observed during the secondcooling step at temperatures just below 50∘C For that it wasimpossible to carry out isothermal AFM tests at temperaturelower than 50∘C

The evolution of the samples surface morphology wasrecoded in terms of distance from a reference position(height) and the characteristic oscillation (amplitude andphase) of the AFM cantilever during the observation timesThe three acquired signals are strictly related to the structureformation on the sample surface during the crystallizationphenomena However in our case the amplitude signal wasfound themost sensible to the change in surfacemorphology

For the present analysis two different tests were consid-ered one with an observed square area with a side of 10 120583mand another withwider area having a side of 30 120583mAs shownin Figure 10 some evidence of crystalline structures appearson the surface after about 1500 s in isothermal conditions

The crystalline structure development was followed byAFM while growing and it was found that the growth frontpropagates by the advancement of primary arms with theregions between the arms filled in by secondary arms growingbehind the primary front [27]

During the isothermal step new crystal aggregates werenot formed but just the development of the previously formedstructures was evident This observation is coherent with thehypothesis of nucleation dependence on temperature andthus during the isothermal step no new stable nuclei areformed

The development of new crystalline structures on thesample surface was followed by means of the evolution of theaverage value of the amplitude signal 119860(119905) during the wholetest

In particular by assuming as initial value of the averagedamplitude (119860

0) the value that 119860(119905) assumes at starting crys-

tallization time the variations of the averaged amplitude foreach time (119860(119905) minus119860

0) divided by the total variation recorded

during the whole test can be transformed into a variationindex (120572AFM(119905))

120572AFM (119905) =int119905

0

(119860 (119905) minus 1198600) 119889119905

intinfin

0

(119860 (119905) minus 1198600) 119889119905

(4)

In Figure 11 is reported for both tests conditions the evo-lution of 120572AFM(119905) as function of the isothermal crystallizationtime

At early stage of the crystallization process a small part ofthe investigated surface is covered by crystalline structure sothe variations of the averaged amplitude signal are very lowAs the crystallization proceeds the variations of the averagedamplitude become larger until a large part of the surface is

0

20

40

60

80

100

0 2000 4000 6000 8000 10000 12000Isothermal time (s)

120572A

FM(mdash

) (

)

10120583m30120583m

Figure 11 Evolution of averaged amplitude of AFM test on a squarearea with sides of 10120583m and 30 120583m

covered by the crystalline structure and therefore the varia-tions of the averaged amplitude are constant

As expected even on the same sample the morphologyappears very different by changing the surface analyzed Thisis clearly shown in Figure 12 where the same sample shows adifferent texture by changing the scanned area

4 Discussions

All the techniques adopted in this work were analysed insuch a way to obtain sigmoidal curves representative of theevolution of the crystallization From all the curves it waspossible to identify an induction time as the time at which themeasured signal deviates from the value that it presents at thestart of the isothermal step when the sample is still moltenwithout any crystallinity A comparison between the resultsobtained with the different techniques presented is shown inFigure 13

Results clearly reveal that the induction time found on theentire range of crystallization is dependent on the techniqueused As expected the observation scale plays an importantrole in its determination Rheology appears to be the leastsensitive technique probably because in order to measurean increase in rheological parameters an interaction amongcrystals is necessary On the contrary AFM tests that are ableto resolve the surface sample at dimensions comparable to theprimary nuclei can detect crystallization at initial stages

5 Conclusions

The morphological development taking place during thecrystallization of polycaprolactone (PCL) was studied usingseveral techniques

Results show that the induction time is dependent on thetechnique used As expected the observation scale plays animportant role in its determination In particular despite itslimitations the AFM that is able to resolve the surface sampleat dimensions comparable to the primary nuclei is able

8 The Scientific World Journal

100

75

50

25

00 25 50 75 100

(120583m)

(a)

300

200

100

00 100 200 300

(120583m)

(b)

Figure 12 AFM amplitude images on different areas after complete crystallization

10

100

1000

10000

41 42 43 44 45 46 47 48 49 50 51

Indu

ctio

n tim

e (s)

DSCPOMRheology

Temperature (∘C)

AFM 10120583mAFM 30120583m

Figure 13 Induction time recorder by the different techniques Thedashed line represents a guide for eyes

to detect crystallization at initial stages On the contraryrheology appears to be the least sensitive technique probablybecause in order to measure an increase in rheologicalparameters an interaction among crystals is necessary DSCand POM techniques supply closer results It suggests that thedefinition of induction time in the polymer crystallization isa vague concept that in any case requires the definition ofthe technique used for its characterization

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] R Pantani I Coccorullo V Speranza and G TitomanlioldquoModeling of morphology evolution in the injection moldingprocess of thermoplastic polymersrdquo Progress in Polymer Sciencevol 30 no 12 pp 1185ndash1222 2005

[2] R Pantani V Speranza A Sorrentino and G TitomanlioldquoMolecular orientation and strain in injectionmoulding of ther-moplasticsrdquo Macromolecular Symposia vol 185 no 1 pp 293ndash307 2002

[3] R Pearce and G J Vancso ldquoImaging of melting and crystalliza-tion of poly(ethylene oxide) in real-time by hot-stage atomicforce microscopyrdquo Macromolecules vol 30 no 19 pp 5843ndash5848 1997

[4] R Pearce and G J Vancso ldquoReal-time imaging of meltingand crystallization in poly(ethylene oxide) by atomic forcemicroscopyrdquo Polymer vol 39 no 5 pp 1237ndash1242 1998

[5] R Pearce and G J Vancso ldquoObservations of crystallizationandmelting in poly(ethylene oxide)poly(methyl methacrylate)blends by hot-stage atomic-force microscopyrdquo Journal of Poly-mer Science B vol 36 no 14 pp 2643ndash2651 1998

[6] J M Schultz and M J Miles ldquoAFM study of morphologicaldevelopment during the melt-crystallization of poly(ethyleneoxide)rdquo Journal of Polymer Science B vol 36 no 13 pp 2311ndash2325 1998

[7] T J McMaster J K Hobbs P J Barham and M J Miles ldquoAFMstudy of in situ real time polymer crystallization and spherulitestructurerdquo Probe Microscopy vol 1 no 1 pp 43ndash56 1997

[8] L Li C-M Chan K L Yeung J-X Li K-M Ng and Y LeildquoDirect observation of growth of lamellae and spherulites of asemicrystalline polymer by AFMrdquoMacromolecules vol 34 no2 pp 316ndash325 2001

[9] J K Hobbs T JMcMasterM JMiles and P J Barham ldquoDirectobservations of the growth of spherulites of poly(hydrox-ybutyrate-co-valerate) using atomic force microscopyrdquo Poly-mer vol 39 no 12 pp 2437ndash2446 1998

The Scientific World Journal 9

[10] L G M Beekmans R Valle and G J Vancso ldquoNucleation andgrowth of poly(120576-caprolactone) on poly(tetrafluoroethylene) byin-situ AFMrdquo Macromolecules vol 35 no 25 pp 9383ndash93902002

[11] W Zhou S Z D Cheng S Putthanarat et al ldquoCrystallizationmelting and morphology of syndiotactic polypropylene frac-tions 4 In situ lamellar single crystal growth and melting indifferent sectorsrdquoMacromolecules vol 33 no 18 pp 6861ndash68682000

[12] Y Jiang D-D Yan X Gao et al ldquoLamellar branching ofpoly(bisphenol A-co-decane) spherulites at different tempera-tures studied by high-temperature AFMrdquo Macromolecules vol36 no 10 pp 3652ndash3655 2003

[13] D A Ivanov Z Amalou and S N Magonov ldquoReal-time evolu-tion of the lamellar organization of poly(ethylene terephthalate)during crystallization from the melt high-temperature atomicforce microscopy studyrdquo Macromolecules vol 34 no 26 pp8944ndash8952 2001

[14] Y Kikkawa H Abe M Fujita T Iwata Y Inoue and Y DoildquoCrystal growth in poly(l-lactide) thin film revealed by insitu atomic force microscopyrdquo Macromolecular Chemistry andPhysics vol 204 no 15 pp 1822ndash1831 2003

[15] R Pantani V Speranza and G Titomanlio ldquoRelevance of crys-tallisation kinetics in the simulation of the injection moldingprocessrdquo International Polymer Processing vol 16 no 1 pp 61ndash71 2001

[16] A Martins W Zhang M Brito U Infante M Romero andF O Soares ldquoIsothermal and nonisothermal crystallization ofpolymers analysis with a shear differential thermal analyzerrdquoReview of Scientific Instruments vol 76 no 10 Article ID 1051052005

[17] W Nagatake T Takahashi Y Masubuchi J-I Takimoto andK Koyama ldquoDevelopment of shear flow thermal rheometer fordirect measurement of crystallization fraction of polymer meltsunder shear deformationrdquo Polymer vol 41 no 2 pp 523ndash5312000

[18] F de Santis A R Vietri and R Pantani ldquoMorphology evolutionduring polymer crystallization simultaneous calorimetric andoptical measurementsrdquoMacromolecular Symposia vol 234 pp7ndash12 2006

[19] A Sorrentino R Pantani and G Titomanlio ldquoKinetics ofmelting and characterization of the thermodynamic and kineticproperties of syndiotactic polystyrenerdquo Journal of PolymerScience B vol 45 no 2 pp 196ndash207 2007

[20] A Ziabicki ldquoApplicability of light transmission technique tostudies of crystalline polymers texturerdquo Kolloid-Zeitschrift ampZeitschrift fur Polymere vol 219 no 1 pp 2ndash12 1967

[21] F L Binsbergen ldquoDepolarization of linearly polarized light bya polycrystalline specimenrdquo Journal of Macromolecular ScienceB vol 4 pp 837ndash851 1970

[22] A Ziabicki and B Misztal-Faraj ldquoApplicability of light depolar-ization technique to crystallization studiesrdquoPolymer vol 46 no7 pp 2395ndash2403 2005

[23] Y P Khanna ldquoRheological mechanism and overview of nucle-ated crystallization kineticsrdquoMacromolecules vol 26 no 14 pp3639ndash3643 1993

[24] S Acierno E di Maio S Iannace and N Grizzuti ldquoStructuredevelopment during crystallization of polycaprolactonerdquo Rheo-logica Acta vol 45 no 4 pp 387ndash392 2006

[25] L Bove and M R Nobile ldquoShear-induced crystallization ofisotactic poly(1-butene)rdquoMacromolecular Symposia vol 185 no1 pp 135ndash147 2002

[26] N V Pogodina V P Lavrenko S Srinivas and H H WinterldquoRheology and structure of isotactic polypropylene near thegel point quiescent and shear-induced crystallizationrdquoPolymervol 42 no 21 pp 9031ndash9043 2001

[27] L G M Beekmans and G J Vancso ldquoReal-time crystalliza-tion study of poly(120576-caprolactone) by hot-stage atomic forcemicroscopyrdquo Polymer vol 41 no 25 pp 8975ndash8981 2000

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Page 8: Research Article Characterization of the Polycaprolactone ...downloads.hindawi.com/journals/tswj/2014/720157.pdfe application of atomic force microscopy (AFM) to polymer system is

8 The Scientific World Journal

100

75

50

25

00 25 50 75 100

(120583m)

(a)

300

200

100

00 100 200 300

(120583m)

(b)

Figure 12 AFM amplitude images on different areas after complete crystallization

10

100

1000

10000

41 42 43 44 45 46 47 48 49 50 51

Indu

ctio

n tim

e (s)

DSCPOMRheology

Temperature (∘C)

AFM 10120583mAFM 30120583m

Figure 13 Induction time recorder by the different techniques Thedashed line represents a guide for eyes

to detect crystallization at initial stages On the contraryrheology appears to be the least sensitive technique probablybecause in order to measure an increase in rheologicalparameters an interaction among crystals is necessary DSCand POM techniques supply closer results It suggests that thedefinition of induction time in the polymer crystallization isa vague concept that in any case requires the definition ofthe technique used for its characterization

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] R Pantani I Coccorullo V Speranza and G TitomanlioldquoModeling of morphology evolution in the injection moldingprocess of thermoplastic polymersrdquo Progress in Polymer Sciencevol 30 no 12 pp 1185ndash1222 2005

[2] R Pantani V Speranza A Sorrentino and G TitomanlioldquoMolecular orientation and strain in injectionmoulding of ther-moplasticsrdquo Macromolecular Symposia vol 185 no 1 pp 293ndash307 2002

[3] R Pearce and G J Vancso ldquoImaging of melting and crystalliza-tion of poly(ethylene oxide) in real-time by hot-stage atomicforce microscopyrdquo Macromolecules vol 30 no 19 pp 5843ndash5848 1997

[4] R Pearce and G J Vancso ldquoReal-time imaging of meltingand crystallization in poly(ethylene oxide) by atomic forcemicroscopyrdquo Polymer vol 39 no 5 pp 1237ndash1242 1998

[5] R Pearce and G J Vancso ldquoObservations of crystallizationandmelting in poly(ethylene oxide)poly(methyl methacrylate)blends by hot-stage atomic-force microscopyrdquo Journal of Poly-mer Science B vol 36 no 14 pp 2643ndash2651 1998

[6] J M Schultz and M J Miles ldquoAFM study of morphologicaldevelopment during the melt-crystallization of poly(ethyleneoxide)rdquo Journal of Polymer Science B vol 36 no 13 pp 2311ndash2325 1998

[7] T J McMaster J K Hobbs P J Barham and M J Miles ldquoAFMstudy of in situ real time polymer crystallization and spherulitestructurerdquo Probe Microscopy vol 1 no 1 pp 43ndash56 1997

[8] L Li C-M Chan K L Yeung J-X Li K-M Ng and Y LeildquoDirect observation of growth of lamellae and spherulites of asemicrystalline polymer by AFMrdquoMacromolecules vol 34 no2 pp 316ndash325 2001

[9] J K Hobbs T JMcMasterM JMiles and P J Barham ldquoDirectobservations of the growth of spherulites of poly(hydrox-ybutyrate-co-valerate) using atomic force microscopyrdquo Poly-mer vol 39 no 12 pp 2437ndash2446 1998

The Scientific World Journal 9

[10] L G M Beekmans R Valle and G J Vancso ldquoNucleation andgrowth of poly(120576-caprolactone) on poly(tetrafluoroethylene) byin-situ AFMrdquo Macromolecules vol 35 no 25 pp 9383ndash93902002

[11] W Zhou S Z D Cheng S Putthanarat et al ldquoCrystallizationmelting and morphology of syndiotactic polypropylene frac-tions 4 In situ lamellar single crystal growth and melting indifferent sectorsrdquoMacromolecules vol 33 no 18 pp 6861ndash68682000

[12] Y Jiang D-D Yan X Gao et al ldquoLamellar branching ofpoly(bisphenol A-co-decane) spherulites at different tempera-tures studied by high-temperature AFMrdquo Macromolecules vol36 no 10 pp 3652ndash3655 2003

[13] D A Ivanov Z Amalou and S N Magonov ldquoReal-time evolu-tion of the lamellar organization of poly(ethylene terephthalate)during crystallization from the melt high-temperature atomicforce microscopy studyrdquo Macromolecules vol 34 no 26 pp8944ndash8952 2001

[14] Y Kikkawa H Abe M Fujita T Iwata Y Inoue and Y DoildquoCrystal growth in poly(l-lactide) thin film revealed by insitu atomic force microscopyrdquo Macromolecular Chemistry andPhysics vol 204 no 15 pp 1822ndash1831 2003

[15] R Pantani V Speranza and G Titomanlio ldquoRelevance of crys-tallisation kinetics in the simulation of the injection moldingprocessrdquo International Polymer Processing vol 16 no 1 pp 61ndash71 2001

[16] A Martins W Zhang M Brito U Infante M Romero andF O Soares ldquoIsothermal and nonisothermal crystallization ofpolymers analysis with a shear differential thermal analyzerrdquoReview of Scientific Instruments vol 76 no 10 Article ID 1051052005

[17] W Nagatake T Takahashi Y Masubuchi J-I Takimoto andK Koyama ldquoDevelopment of shear flow thermal rheometer fordirect measurement of crystallization fraction of polymer meltsunder shear deformationrdquo Polymer vol 41 no 2 pp 523ndash5312000

[18] F de Santis A R Vietri and R Pantani ldquoMorphology evolutionduring polymer crystallization simultaneous calorimetric andoptical measurementsrdquoMacromolecular Symposia vol 234 pp7ndash12 2006

[19] A Sorrentino R Pantani and G Titomanlio ldquoKinetics ofmelting and characterization of the thermodynamic and kineticproperties of syndiotactic polystyrenerdquo Journal of PolymerScience B vol 45 no 2 pp 196ndash207 2007

[20] A Ziabicki ldquoApplicability of light transmission technique tostudies of crystalline polymers texturerdquo Kolloid-Zeitschrift ampZeitschrift fur Polymere vol 219 no 1 pp 2ndash12 1967

[21] F L Binsbergen ldquoDepolarization of linearly polarized light bya polycrystalline specimenrdquo Journal of Macromolecular ScienceB vol 4 pp 837ndash851 1970

[22] A Ziabicki and B Misztal-Faraj ldquoApplicability of light depolar-ization technique to crystallization studiesrdquoPolymer vol 46 no7 pp 2395ndash2403 2005

[23] Y P Khanna ldquoRheological mechanism and overview of nucle-ated crystallization kineticsrdquoMacromolecules vol 26 no 14 pp3639ndash3643 1993

[24] S Acierno E di Maio S Iannace and N Grizzuti ldquoStructuredevelopment during crystallization of polycaprolactonerdquo Rheo-logica Acta vol 45 no 4 pp 387ndash392 2006

[25] L Bove and M R Nobile ldquoShear-induced crystallization ofisotactic poly(1-butene)rdquoMacromolecular Symposia vol 185 no1 pp 135ndash147 2002

[26] N V Pogodina V P Lavrenko S Srinivas and H H WinterldquoRheology and structure of isotactic polypropylene near thegel point quiescent and shear-induced crystallizationrdquoPolymervol 42 no 21 pp 9031ndash9043 2001

[27] L G M Beekmans and G J Vancso ldquoReal-time crystalliza-tion study of poly(120576-caprolactone) by hot-stage atomic forcemicroscopyrdquo Polymer vol 41 no 25 pp 8975ndash8981 2000

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Page 9: Research Article Characterization of the Polycaprolactone ...downloads.hindawi.com/journals/tswj/2014/720157.pdfe application of atomic force microscopy (AFM) to polymer system is

The Scientific World Journal 9

[10] L G M Beekmans R Valle and G J Vancso ldquoNucleation andgrowth of poly(120576-caprolactone) on poly(tetrafluoroethylene) byin-situ AFMrdquo Macromolecules vol 35 no 25 pp 9383ndash93902002

[11] W Zhou S Z D Cheng S Putthanarat et al ldquoCrystallizationmelting and morphology of syndiotactic polypropylene frac-tions 4 In situ lamellar single crystal growth and melting indifferent sectorsrdquoMacromolecules vol 33 no 18 pp 6861ndash68682000

[12] Y Jiang D-D Yan X Gao et al ldquoLamellar branching ofpoly(bisphenol A-co-decane) spherulites at different tempera-tures studied by high-temperature AFMrdquo Macromolecules vol36 no 10 pp 3652ndash3655 2003

[13] D A Ivanov Z Amalou and S N Magonov ldquoReal-time evolu-tion of the lamellar organization of poly(ethylene terephthalate)during crystallization from the melt high-temperature atomicforce microscopy studyrdquo Macromolecules vol 34 no 26 pp8944ndash8952 2001

[14] Y Kikkawa H Abe M Fujita T Iwata Y Inoue and Y DoildquoCrystal growth in poly(l-lactide) thin film revealed by insitu atomic force microscopyrdquo Macromolecular Chemistry andPhysics vol 204 no 15 pp 1822ndash1831 2003

[15] R Pantani V Speranza and G Titomanlio ldquoRelevance of crys-tallisation kinetics in the simulation of the injection moldingprocessrdquo International Polymer Processing vol 16 no 1 pp 61ndash71 2001

[16] A Martins W Zhang M Brito U Infante M Romero andF O Soares ldquoIsothermal and nonisothermal crystallization ofpolymers analysis with a shear differential thermal analyzerrdquoReview of Scientific Instruments vol 76 no 10 Article ID 1051052005

[17] W Nagatake T Takahashi Y Masubuchi J-I Takimoto andK Koyama ldquoDevelopment of shear flow thermal rheometer fordirect measurement of crystallization fraction of polymer meltsunder shear deformationrdquo Polymer vol 41 no 2 pp 523ndash5312000

[18] F de Santis A R Vietri and R Pantani ldquoMorphology evolutionduring polymer crystallization simultaneous calorimetric andoptical measurementsrdquoMacromolecular Symposia vol 234 pp7ndash12 2006

[19] A Sorrentino R Pantani and G Titomanlio ldquoKinetics ofmelting and characterization of the thermodynamic and kineticproperties of syndiotactic polystyrenerdquo Journal of PolymerScience B vol 45 no 2 pp 196ndash207 2007

[20] A Ziabicki ldquoApplicability of light transmission technique tostudies of crystalline polymers texturerdquo Kolloid-Zeitschrift ampZeitschrift fur Polymere vol 219 no 1 pp 2ndash12 1967

[21] F L Binsbergen ldquoDepolarization of linearly polarized light bya polycrystalline specimenrdquo Journal of Macromolecular ScienceB vol 4 pp 837ndash851 1970

[22] A Ziabicki and B Misztal-Faraj ldquoApplicability of light depolar-ization technique to crystallization studiesrdquoPolymer vol 46 no7 pp 2395ndash2403 2005

[23] Y P Khanna ldquoRheological mechanism and overview of nucle-ated crystallization kineticsrdquoMacromolecules vol 26 no 14 pp3639ndash3643 1993

[24] S Acierno E di Maio S Iannace and N Grizzuti ldquoStructuredevelopment during crystallization of polycaprolactonerdquo Rheo-logica Acta vol 45 no 4 pp 387ndash392 2006

[25] L Bove and M R Nobile ldquoShear-induced crystallization ofisotactic poly(1-butene)rdquoMacromolecular Symposia vol 185 no1 pp 135ndash147 2002

[26] N V Pogodina V P Lavrenko S Srinivas and H H WinterldquoRheology and structure of isotactic polypropylene near thegel point quiescent and shear-induced crystallizationrdquoPolymervol 42 no 21 pp 9031ndash9043 2001

[27] L G M Beekmans and G J Vancso ldquoReal-time crystalliza-tion study of poly(120576-caprolactone) by hot-stage atomic forcemicroscopyrdquo Polymer vol 41 no 25 pp 8975ndash8981 2000

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Page 10: Research Article Characterization of the Polycaprolactone ...downloads.hindawi.com/journals/tswj/2014/720157.pdfe application of atomic force microscopy (AFM) to polymer system is

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials