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Hindawi Publishing CorporationInternational Journal of Polymer ScienceVolume 2013 Article ID 238567 11 pageshttpdxdoiorg1011552013238567

Review ArticleOptical Properties of the Self-Assembling PolymericColloidal Systems

Alexandra Mocanu Edina Rusen and Aurel Diacon

Department of Polymer Science University Politehnica of Bucharest 149 Calea Victoriei 010072 Bucharest Romania

Correspondence should be addressed to Edina Rusen edina rusenyahoocom

Received 11 March 2013 Revised 17 June 2013 Accepted 20 June 2013

Academic Editor Haojun Liang

Copyright copy 2013 Alexandra Mocanu et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

In the last decade optical materials have gained much interest due to the high number of possible applications involving pathor intensity control and filtering of light The continuous emerging technology in the field of electrooptical devices or medicalapplications allowed the development of new innovative cost effective processes to obtain optical materials suited for futureapplications such as hybridpolymeric solar cells lasers polymeric optical fibers and chemo- and biosensing devices Consideringthe above the aim of this review is to present recent studies in the field of photonic crystals involving the use of polymericmaterials

1 Photonic Crystals

Nanomaterials with well-defined 3D repetitive arrays havefound application in photonic devices sensors selectivemembranes and even microchips

Compared to a classic crystalline array colloidal sphericalparticles replace the molecules atoms or ions in hexagonalclose packed (HCP) structure or cubic close packed (CCP)structures [1ndash3] (Figure 1)

Colloidal particles are able through self-assembly pro-cesses to be arranged into 3D structures leading to col-loidal crystals The resulting materials revealed interestingproperties presenting similar optical characteristics withsynthetic opal and photonic crystals (Figure 2) One of themost facile routes for obtaining photonic crystals is basedon the employment of polymer colloids with self-assemblingproperties [3ndash5]

A photonic crystal is a periodic nanostructured materialthat influences the propagation of electromagnetic waves in asimilar manner as a semiconductor does for electrons [3]

Although photonic crystals have been studied since 1887with one of the pioneers being Rayleigh [6] the term hasbeen introduced only in 1987 after the papers of two physicistworking independently Yablonovitch and John [7 8]

In order to understand the behavior of photons inside aphotonic crystal it is possible to compare it with the motionof electrons and vacancies in a semiconductor material asmentioned above A proper example of photonic crystalsoccurring in nature is opals which contain a natural peri-odic microstructure of silica microspheres of 15ndash900 nmresponsible for their iridescent color [9]This structure allowsthe propagation of the photons through the crystal whilethe interaction between the silica spheres and light makespossible the formation of allowed and forbidden energybands also known as band gaps or stop bands [8] Thus thepropagation of the electromagnetic waves is forbidden forspecific wavelengths

Therefore a photonic crystal is a powerful tool for lightmodulation in certain directions of space Exploiting theseproperties photonic crystals have been used in many opticalapplications such as the use in sensors and monitors [1011] bioassays [12 13] colour displays [14 15] solar energy[16] and lasers [17 18] For all applications involving PCsone of the key parameters that have to be controlled is theband-gap position The stop-band value depends primarilyon three factors [19ndash22] the refractive index contrast betweenthe dielectric components (solid and air usually) the latticeconstant (the spacing between the spheres) and the filling

2 International Journal of Polymer Science

AB

A

BA

BACBACBA

Figure 1 Three-dimensional arrays (a) HCP (b) CCP [3]

factor (volume of the colloids related to the volume ofsurroundingmedia) In addition one of themost challengingapplications consists in fabricating photonic crystals with 3Dband gap around 155 120583m representing the wavelength usedin optical fibers [23]

2 Polymeric Photonic Crystals

In order to obtain colloidal crystals the most commonmethods consist in surfactant-free emulsion polymerization[5 24] precipitation polymerization [25 26] dispersionpolymerization [27] and seeded emulsion polymerization[28] The absence of surfactants leads to polymer latex ofhigh purity and at the same time the polymerization param-eters (temperature initiator and monomer concentrationsstirring etc) are facile to control The final monodispersepolymer particles represent a class of materials that can beeasily functionalized on the surface therefore increasing thenumber of possible applications [1]

As it was specified in the previous section colloidal crys-tals represent HCP or CCP structures consisting of colloidalmicrospheres ranging from 100 nm to 1 120583m Depending onthe arrangement parameters the photons are forbidden topropagate inside colloidal crystals in certain directions forspecific wavelengths If the lattice potential is strong enoughthe gap might extend to all possible directions resulting in acomplete band gap [29] This property allows the control ofthe light that interacts with the colloidal crystal

Taking this into account it is easy to realize that one ofthemost important optical properties of the colloidal crystalsconsists in light diffraction according to Braggrsquos law

21 Braggrsquos Law In order to better understand the phe-nomenon that occurs inside a polymer photonic crystal it isnecessary to analyze the path of an incident beam that travelsthrough the crystal planes

The diagram below [30] (Figure 3) explains the pathwaythe beam B which represents the extra distance traveled bybeam A Perpendicular lines (l) lines were drawn to bothrays Following thismethod two right triangles were obtained[30]

The angle marked 120579 also called Braggs angle can becalculated from these triangles as sin 120579 = 119904119889 Therefore theextra distance is 2119904 long or 2119889 sin 120579 long This value is equal

with a number of wavelengths (119899) for a strong beam (Braggrsquoslaw)

119899120582 = 2119889 sin 0 (1)

When the Bragg equation is satisfied the angle formedby the diffracted beam with the crystal plane is equal to theone between by the incident beam and the same crystal planeIn this situation diffraction is similar to a reflection from amirror (Braggs mirror effect) where the angle of incidence isidentical to the angle of reflection [30]

In the case of molecular atomic or ionic crystals theinterplanar spacing 119889 is in the range of A thus having thecapacity of diffracting X-rays In the case of colloidal crystals119889 is in the range of 100 nm which implies the diffractionof light with wavelengths of the same order of magnitude(400ndash800 nm) Therefore the colloidal crystal will diffractlight with wavelengths corresponding to violet-blue-greenand transmit it in the complementary radiation (orange-red)of visible light

22 Braggrsquos Law on Colloidal Crystal The examination ofa colloidal dispersion (Figure 4) during and after solventevaporation allows the observation of iridescence in differentareas of the visible spectrum due to diffraction of the light inaccordance with Braggrsquos law [31]

The optical microscopy shows that the distance betweenthe defaults due to water evaporation is only 150ndash200120583mwhich proves the high quality of the film respectively ofthe obtained opal [32] The crystallization process revealspermanent changes in the color of the colloidal dispersionIn the first step the dispersion is white due to Mie scatteringand 119889 is larger than polymer particles [33] In the second stepthe colloidal dispersion changes its colors as a consequence ofreducing the interplanar distance

Figure 5(a) shows a well-ordered close packed structurewith a triangular arrangement that can be attributed to planes(111) of a CCP system [9 31 34] Moreover the (fast fouriertransform) FFT of the image (Figure 5(b)) displays sharppeaks confirming the existence of long-range crystallineorder

According to Braggrsquos law the change of the angle betweenthe incident radiation and photonic crystal leads to notablechanges of the reflected wavelength respectively of theobserved color (Figure 6) [35 36]

UV-VIS spectra of polymer photonic crystals indicatein many cases sharp peaks which confirm the existence ofhighly ordered structures due to Braggs reflection of periodicarrangement of the polymer particles [37ndash40]

Figure 7(b) represents the reflection spectra of poly-mer colloidal crystals with different size particles (178 nm211 nm 235 nm and 270 nm) corresponding to photograph(Figure 7(a)) [41]

Moreover these materials show structural color changes(Figure 8) under mechanical stress In this case the photoniccrystal film deposited on a plastic plate changed from red togreen as result of themodification of the interplanar distancewhich is thus a change in thewavelength of the diffracted light[37]

International Journal of Polymer Science 3

(a) (b)

Figure 2 (a) Synthetic opal (b) structure of a photonic crystal [4]

AB

AB

985747985747

120582

d

120579 120579

s

Figure 3 The diffraction of the light by crystal planes [30]

(a)

(b)

(c)

Figure 4 Light diffraction iridescence of polymer colloidal spheres(a) optical microscopy (b) photo recorded at an angle of 45∘following thermal treatment (c) photo recorded at an angle of 90∘following thermal treatment [31]

Although until now polymer photonic crystals were notexpected to exhibit full stop bands they were easy to prepareleading to materials that allow the control of the light thatinteracts with the crystalline colloidal arrays [3 42]

3 Applications of the PolymericPhotonic Crystals

In the last years polymeric photonic crystals found appli-cation in optical devices [43ndash45] and sensors [46] or as

(a)

(b)

Figure 5 (a) AFM image of the top surface of the opal and (b) FFTof the image [31]

templates for other interesting porous-media applicationstaking advantage of their optical properties composition ormorphology [26 47 48]

31 Templates for Porous-Media Applications Polymer col-loidal crystals without complete band gaps can still be used astemplates to create new structures with complete band gaps[49]

The first step in obtaining inverse opal is to arrange byself-assembly polymer colloidal spheres into periodic arrays(Figure 9) The voids between the polymer particles can thenbe filled with different solutions that play the role of matrixAfter this procedure the polymer spheres are removed bydissolution or calcination leaving air spaces in thematrixTheresulting system is a photonic crystal with different opticalproperties (incremental shift and broadening with respect tothose in spectra of parent opals) (Figure 10)

Waterhouse et al [9] obtained inverse opal structuresby depositing inorganic particles such as silica titania andceria respectively by a sol-gel method in the voids of


(a) (b)

Figure 6 Reflected colors of colloidal dispersions registered at different angles [36]

(a)

400 600 800

Refle

ctan

ce (

)

178 nm

211 nm 235 nm

270 nm

Wavelength (nm)

100

80

60

40

20

0

(b)

Figure 7 Polymer colloidal dispersions (a) photograph taken at normal incidence (b) reflection spectra [41]

Figure 8 Structural color change in a crystal film after mechanicalstress [37]

a polymeric photonic film The poly(methyl methacrylate)polymer self-assembled spheres (Figure 11(b)) were removedby calcination at 550∘C The process resulted in obtaining amacroporous matrix with CCP ordered air spheres separatedby inorganic nanoparticles according to the layout presentedbelow (Figure 11(a)) The macroporous materials formedwere characterized by SEM analysis in comparison with thepolymer poly(methyl methacrylate) templates in order toput into evidence the inverse opal structures highlighted inFigure 11(c) [9]

Macroporous 3D structures were obtained also by a dip-coating procedure explained byMoon et al [50] In this study

40302010

001 1 10 100 1000 10000

Figure 9 Polymer colloidal crystal obtained by soap free emulsionpolymerization and DLS spectrum [65]

they obtained porous cylinders with interconnected air voidsusing commercial cylindrical glass fiber of 60 and 100 120583mrespectively

The fiber was dipped into the colloidal dispersion Thecolloidal poly(styrene) particles self-assembled in a CCP


Template spherical network

(a)

Air sphere

(b)

Figure 10 Unit cell of an infiltrated opal (a) unit cell of an inverse opal (b) [66]

PMMA colloids Colloidal crystal (CC)

Inverse opal Infiltrated CC(a)

(b)

(c)

Figure 11 Fabrication scheme of an inverse opal (a) poly(methyl methacrylate) colloidal spheres (b) TiO2

inverse opal (c) [9]

AB

C

Figure 12 Schematic illustration of the self-assembly of colloidalspheres on a cylindrical glass fiber (A) and the inverted structurewith glass fiber core (B) respectively with hollow core (C) [50]

structure on the cylindrical glass substrate during the evap-oration of the solvent Then a solution of polyurethanewas infiltrated between the poly(styrene) arranged spheresand polymerized The macroporous cylindrical structurewas obtained on a glass fiber support by dissolving thepoly(styrene) spheres By removing the inner core an invertedporous structure with hollow core was obtained (Figures 12and 13)

Moreover the authors demonstrated that these structureshave a controllable pore size by using colloidal particleswith different dimensions Therefore these porous fibers aresuitable for separation ofmembranes or catalyst support [50]

Kalinina et al [51] proposed a new method in orderto obtain materials with optically sensitive matrix startingfrom monodisperse core-shell colloidal particles In the firststep of this study the particles that possess a hard coreof poly(methyl methacrylate) and a relatively soft shell ofpoly(butyl methacrylate) are self-assembled in a crystallinearray The film is annealed at a temperature that is above theglass transition temperature 119879

119892of the polymeric shell and

below the 119879119892of the polymeric core At this temperature the

shell fills the air spaces between the colloidal particles leavinga matrix with intact cores and totally different optical prop-erties towards the initial polymer film The incorporation ofa fluorescent dye during the polymerization process of theshell forming polymer resulted in a substantial reduction inoptical contrast between the particles and the matrix [51]

The type of the matrix often influences the specific appli-cations of inverse opal structures A polymer matrix formedby poly(methyl methacrylate) polystyrene polyurethane orelectroconducting polymers is suitable for optical devicesFor example polypyrrole polythiophene or polyaniline films


(a) (b)

Figure 13 Cross-section of polyurethane fiber with glass core (a) and with hollow core (b) respectively [50]

with inverse opal structure are assembled on ITO conductiveglass used in solar cells [52] It is worth mentioning the factthat an inorganic matrix formed by semiconductors (like GeTiO2 InP and CdSe) or other metal compounds [53] found

application in realization of infrared active optical materialsdue to their high refractive index [54 55] while polymerinverse opals can be used in medicine as scaffolds for tissueengineering or cell culture [56] (Figure 14)

32 Sensors The refractive index is a result of the interplanardistance and the type of packing of the polymerinorganicspheres according to Braggrsquos law Practically the stop bandis directly proportional with the interplanar distance 119889 Inother words any variation of 119889 should determine a shift inthe diffraction peak of the reflected light This property ofthe crystalline 3D arrays makes these materials suitable foroptical sensors [1]

Polymer photonic crystals are used in optical sensorscoupled to a transduction device that identifies the opti-cal diffraction shifts that occur once the external mediumchanges

Optical sensors based on colloidal crystals (sometimesembedded in hydrogels) are known for their simplicity andlow cost and efficiency In the last years remarkable resultsto the preparation of photonic crystal sensors that are highlysensitive to a series of pH [57] temperature [58] solventswelling [59] ionic strength ions [60] and biomolecules [61]have been obtained

In addition colloidal crystals were also used to developnew sensors for the detection of endocrine-disrupting chemi-cals like bisphenolA (BPA) at low costs Guo et al [62] explainthe concept of photonic crystals-based sensors using com-bined photonic crystal technology and molecular imprintingtechniques First poly(methyl methacrylate) spheres weremodifiedwith nanocavities derived from the BPA-imprintingmethod The modification of the colloidal spheres by thesetechniques affords nanocavities distributed in the polymericcrystalline array which allow the photonic crystal sensorto identify BPA specifically Using these procedures thechanges in diffraction intensity which are related to BPAconcentrations can be observed (Figure 15) even at very lowconcentrations of BPA ranging from 1 ngmL to 1120583gmL

In a recent study Hu et al [63] developed an opticalsensor sensitive for anions starting from the properties of anionic liquid based monomer and photonic crystals

Therefore a photopolymerization was conducted usingan imidazolium-based ionic liquid monomer (1-(2-acryloylo-xyhexyl)-3-methylimidazolium bromide) with methyl metha-crylate a cross-linker and initiator in a solvent mixture(methanolchloroform) and infiltrated in a photonic crystalconsisting of silica colloidal particles After removal of theinorganic silica particles a porous inverse opal film wasobtained (Figure 16(a))

The new photonic ionic liquid films were immersedin anionic aqueous solutions The anions bonded onto thefilm surface reducing its hydrophilicity As a consequencethe volume of the film changed (shrunk) leading to strongmodifications of the resulting photonic structures stop bands(Figure 16(b))

In Figure 16(c) the color changes can also be observedwith naked eye representing a much easier and in-expensivemethod for identifying anions

Moreover it was also possible to identify the polarity ofdifferent solvents using these photonic ionic liquid films dueto the interactions between the terminal groups of the ionicliquid and solvent [63]

Although the use of ionic liquids in optical sensors islimited due to time-consuming or difficult synthetic proce-dures this new approach based on photonic colloidal crystalsafforded a system for rapid naked-eye detection of anions

Considering that there are about 108 ionic liquids [63] thisprocedure might allow the development of more ionic liquidmonomers for advanced applications in photonic crystals

33 Optical Devices Recently the propagationmechanism oflight inside 3D polymer colloidal crystals gained much inter-est leading to an important progress in photonic applicationssuch as microlasers waveguides or photonic crystal fibers[45]

In other words Furumi et al [18] fabricated a colloidalcrystal film using 200 nm polystyrene colloidal particlesfollowed by the thermal polymerization of dimethylsiloxanein the air voids of the 3D structure Next step consisted in


(a) (b)

(c) (d)

Figure 14 SEM images of the chitosan inverse opal scaffold (a) side view (b) top view (c) a magnified view of the top surface and (d) amagnified view of the side wall in a pore The black line in (a) represents the edge of the scaffold [56]

BPAVoid nanocavityBPA-imprintednanocavity

Inte

nsity

Wavelength

Opticalprobe

Incidencelight

Reflectionlight

BPA-imprintedphotonic crystal

Remove the BPAmolecules

Add the BPA molecules andoptical characterization

Figure 15 Experimental procedure for the detection of BPA using a photonic crystal sensor [62]


(a)

020

015

010

005550 600 650 700 750

Abso

rban

ce

Wavelength (nm)

WaterNaBrNH4NO3

NaBF4

NaClO4

NH4PF6

LiTf2N

(b)

Water Brminus Tf2NminusNO3minus BF4

minus ClO4minus PF6

minus

(c)

Figure 16 SEM image of the inverseopal photonic ionic liquid film (a) Stop-band shifts of the film upon soaking in various aqueous anionicsolutions (b) Color changes of the film after anions aqueous solutions treatment (c) [63]

Photonic band effectOptical excitation

Laser emission

PS particlePDMS elastomer

Fluorescent Rh dyeUV-curable PEG-DA

Figure 17 A schematic illustration of the colloidal crystal laser(CCL) proposed by Furumi et al A light-emitting planar defectof Rhodamine (Rh)PEG-DA is sandwiched between a pair of CCfilms of PS particles stabilized in PDMS elastomer The left-handpicture represents a cross-sectional scanning electron microscopy(SEM) image of the magnified light-emitting planar defect betweenthe PSPDMS CC films The white scale bar represents 2 120583m [18]

introducing a light emitting planar defect based on fluo-rescent dye (rhodamine 640) dispersed in a poly(ethyleneglycol) diacrylate film in order to obtain a laser effectresulting in sandwich-type structure (Figure 17)

Therefore the plastic film through excitation with a greenwavelength affords a red laser emission as suggested inFigure 18

Figure 18 Laser effect of the plastic film [18]

Photonic crystal microfibers were obtained by Mıguezet al [64] using an inverted silicon colloidal crystal Firstin rectangular microchannels colloidal particles of silicaranging from 250 nm to 900 nm were self-assembled in FCCstructure After a coating process of the silica spheres inorder to control the connectivity between the particles themicrochannels are infiltratedwith silicon by a chemical vapordeposition method The silicon fills the interstitial spacesfrom the silica colloidal structure In order to obtain the 3Dsilicon inverse structure the silica particles are removed andthe resulted microfibers are investigated by SEM and opticalmicroscopy (Figure 19)

In Figure 19(a) the presented microfibers have severalmicrometers in length An interesting optical behavior ofthe microfibers which due to the various degrees of siliconinfiltration exhibit different modulations of the dielectric


120120583m

40120583m

75 120583m 1120583m

(a) (b)

(c) (d)

Figure 19 Images of inverse silicon microfibers (a) SEM image of a bunch of fibers collected using a sticky carbon tape (b) optical picture oftwo fibers presenting a different degree of infiltration thus presenting different colors ((c) (d)) details of the bottom surface of a free standinginverted colloidal crystal fiber showing the high degree of connectivity between the spherical cavities [64]

constant in the structure thus resulting in distinct reflectedcolors is illustrated in Figure 19(b) [64]

Compared to inorganic fibers this method provided asimple synthesis procedure for obtaining microfibers withhigher flexibility and controllable optical properties Asthe authors suggested [64] the optical properties of thesynthesized photonic crystal microfibers could make themsuitable in future for optical components in microcomputersreplacing the conventional semiconductor nanowires

In conclusion the aim of this review has been to brieflypresent the concept of photonic crystals and the advantagesof obtaining these structures using polymeric materials Theproperty of self-assembling remains one of the key character-istics that motivate the use of these materials Control of theself-assembly process as well as of the morphology attainedallows the elaboration of newmaterials capable of interactingwith light and able to be incorporated into novel devices

The doping with various dyes the interaction withinorganic particles in hybrid systems innovative synthesistechniques for specific applications (molecularly imprintedpolymers synthesis in the presence of ionic liquids) consti-tute new topics for novel and innovative applications basedon polymeric colloidal particles and photonic crystals

Acknowledgment

Theauthors would like to acknowledge thank for the financialsupport provided by the National Authority for ScientificResearch from the Ministry of Education Research and

Youth of Romania through the PN-II-PT-PCCA-2011-32-0042-RPETUM Project

References

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[2] Y Chen W T Ford N F Materer and D Teeters ldquoConversionof colloidal crystals to polymer nets turning latex particlesinside outrdquo Chemistry of Materials vol 13 no 8 pp 2697ndash27042001

[3] J Zhang Z Sun and B Yang ldquoSelf-assembly of photoniccrystals from polymer colloidsrdquo Current Opinion in Colloid andInterface Science vol 14 no 2 pp 103ndash114 2009

[4] S A Rinne F Garcıa-Santamarıa and P V Braun ldquoEmbeddedcavities and waveguides in three-dimensional silicon photoniccrystalsrdquo Nature Photonics vol 2 no 1 pp 52ndash56 2008

[5] A Herzog Cardoso C A P Leite M E D Zaniquelli andF Galembeck ldquoEasy polymer latex self-assembly and colloidalcrystal formation the case of poly[styrene-co-(2-hydroxyethylmethacrylate)]rdquo Colloids and Surfaces A vol 144 no 1ndash3 pp207ndash217 1998

[6] L Rayleigh ldquoXXVI On the remarkable phenomenon of crys-talline reflexion described by Prof Stokesrdquo Philosophical Maga-zine Series 5 vol 26 no 160 pp 256ndash265 1888

[7] E Yablonovitch ldquoInhibited spontaneous emission in solid-statephysics and electronicsrdquo Physical Review Letters vol 58 no 20pp 2059ndash2062 1987

[8] S John ldquoStrong localization of photons in certain disordereddielectric superlatticesrdquo Physical Review Letters vol 58 no 23pp 2486ndash2489 1987


[9] G I N Waterhouse and M R Waterland ldquoOpal and inverseopal photonic crystals fabrication and characterizationrdquo Poly-hedron vol 26 no 2 pp 356ndash368 2007

[10] X Zhao Y Cao F Ito et al ldquoColloidal crystal beads as supportsfor biomolecular screeningrdquo Angewandte Chemie vol 45 no41 pp 6835ndash6838 2006

[11] E Rusen A Mocanu A Diacon and B Marculescu ldquoFluores-cence enhancement of rhodamine B in the presence of photoniccrystal heterostructuresrdquo Journal of Physical Chemistry C vol115 no 30 pp 14947ndash14953 2011

[12] Y Zhao X Zhao and Z Gu ldquoPhotonic crystals in bioassaysrdquoAdvanced Functional Materials vol 20 no 18 pp 2970ndash29882010

[13] A Mocanu B Marculescu R Somoghi F Miculescu CBoscornea and I C Stancu ldquoFluorescence enhancement forthe complex PAMAM-BSA in the presence of photonic crystalheterostructuresrdquo Colloids and Surfaces A vol 392 no 1 pp288ndash293 2011

[14] A C Arsenault D P Puzzo A Ghoussoub I Manners andG A Ozin ldquoDevelopment of photonic crystal composites fordisplay applicationsrdquo Journal of the Society for InformationDisplay vol 15 no 12 pp 1095ndash1098 2007

[15] A C Arsenault D P Puzzo I Manners and G A OzinldquoPhotonic-crystal full-colour displaysrdquo Nature Photonics vol 1no 8 pp 468ndash472 2007

[16] Z Ye J M Park K Constant T G Kim and K M Ho ldquoPho-tonic crystal energy-related applicationsrdquo Journal of Photonicsfor Energy vol 2 no 1 Article ID 021012 2012

[17] J R Lawrence Y Ying P Jiang and S H Foulger ldquoDynamictuning of organic lasers with colloidal crystalsrdquo AdvancedMaterials vol 18 no 3 pp 300ndash303 2006

[18] S Furumi H Fudouzi H T Miyazaki and Y Sakka ldquoFlexiblepolymer colloidal-crystal lasers with a light-emitting planardefectrdquo Advanced Materials vol 19 no 16 pp 2067ndash2072 2007

[19] J Ge and Y Yin ldquoResponsive photonic crystalsrdquo AngewandteChemie vol 50 no 7 pp 1492ndash1522 2011

[20] C I Aguirre E Reguera and A Stein ldquoTunable colors inopals and inverse opal photonic crystalsrdquo Advanced FunctionalMaterials vol 20 no 16 pp 2565ndash2578 2010

[21] S Furumi H Fudouzi and T Sawada ldquoSelf-organized colloidalcrystals for photonics and laser applicationsrdquo Laser and Photon-ics Reviews vol 4 no 2 pp 205ndash220 2010

[22] C T Chan and J A Yeh ldquoTunable photonic crystal based oncapillary attraction and repulsionrdquo Optics Express vol 18 no20 pp 20894ndash20899 2010

[23] S S Mishra and V K Singh ldquoComparative study of fun-damental properties of honey comb photonic crystal fiber at155 120583mwavelengthrdquo Journal ofMicrowaves Optoelectronics andElectromagnetic Applications vol 10 no 2 pp 343ndash354 2011

[24] Y Chen and S Sajjadi ldquoParticle formation and growth in ab ini-tio emulsifier-free emulsion polymerisation under monomer-starved conditionsrdquo Polymer vol 50 no 2 pp 357ndash365 2009

[25] D Suzuki J G McGrath H Kawaguchi and L A Lyon ldquoCol-loidal crystals of thermosensitive coreshell hybrid microgelsrdquoJournal of Physical Chemistry C vol 111 no 15 pp 5667ndash56722007

[26] X Xu and S A Asher ldquoSynthesis and utilization of monodis-perse hollow polymeric particles in photonic crystalsrdquo Journalof the American Chemical Society vol 126 no 25 pp 7940ndash7945 2004

[27] SM Klein V NManoharan D J Pine and F F Lange ldquoPrepa-ration of monodisperse PMMA microspheres in nonpolarsolvents by dispersion polymerization with a macromonomericstabilizerrdquo Colloid and Polymer Science vol 282 no 1 pp 7ndash132003

[28] J W Kim J H Ryu and K D Suh ldquoMonodisperse micron-sized macroporous poly(styrene-co-divinylbenzene) particlesby seeded polymerizationrdquo Colloid and Polymer Science vol279 no 2 pp 146ndash152 2001

[29] X Wu A Yamilov X Liu et al ldquoUltraviolet photonic crystallaserrdquo Applied Physics Letters vol 85 no 17 pp 3657ndash36592004

[30] E A Wood Crystals and Light An Introduction to OpticalCrystallography Dover Publications 1977

[31] E Rusen A Mocanu C Corobea and B Marculescu ldquoObtain-ing of monodisperse particles through soap-free polymeriza-tion in the presence of C60rdquo Colloids and Surfaces A vol 355no 1ndash3 pp 23ndash28 2010

[32] H Fudouzi ldquoNovel coating method for artificial opal films andits process analysisrdquoColloids and Surfaces A vol 311 no 1ndash3 pp11ndash15 2007

[33] H Fudouzi ldquoFabricating high-quality opal films with uniformstructure over a large areardquo Journal of Colloid and InterfaceScience vol 275 no 1 pp 277ndash283 2004

[34] X He YThomann R J Leyrer and J Rieger ldquoIridescent colorsfrom films made of polymeric core-shell particlesrdquo PolymerBulletin vol 57 no 5 pp 785ndash796 2006

[35] M Allard E H Sargent E Kumacheva and O KalininaldquoCharacterization of internal order of colloidal crystals byoptical diffractionrdquo Optical and Quantum Electronics vol 34no 1ndash3 pp 27ndash36 2002

[36] P Jiang G N Ostojic R Narat D M Mittleman and V LColvin ldquoThe fabrication and bandgap engineering of photonicmultilayersrdquo Advanced Materials vol 13 no 6 pp 389ndash3932001

[37] H Fudouzi ldquoOptical properties caused by periodical arraystructure with colloidal particles and their applicationsrdquoAdvanced Powder Technology vol 20 no 5 pp 502ndash508 2009

[38] S Reculusa P Masse and S Ravaine ldquoThree-dimensionalcolloidal crystals with a well-defined architecturerdquo Journal ofColloid and Interface Science vol 279 no 2 pp 471ndash478 2004

[39] H Zhou S Xu Z Sun X Du and J Xie ldquoRapid determinationof colloidal crystalrsquos structure by reflection spectrumrdquo Colloidsand Surfaces A vol 375 no 1ndash3 pp 50ndash54 2011

[40] A Emoto E Uchida and T Fukuda ldquoFabrication and opticalproperties of binary colloidal crystal monolayers consisting ofmicro- and nano-polystyrene spheresrdquo Colloids and Surfaces Avol 396 pp 189ndash194 2012

[41] Z Z Gu H Chen S Zhang L Sun Z Xie and Y Ge ldquoRapidsynthesis of monodisperse polymer spheres for self-assembledphotonic crystalsrdquo Colloids and Surfaces A vol 302 no 1ndash3 pp312ndash319 2007

[42] E Yablonovitch T J Gmitter and KM Leung ldquoPhotonic bandstructure the face-centered-cubic case employing nonsphericalatomsrdquo Physical Review Letters vol 67 no 17 pp 2295ndash22981991

[43] W H Wong K K Liu K S Chan and E Y B Pun ldquoPolymerdevices for photonic applicationsrdquo Journal of Crystal Growthvol 288 no 1 pp 100ndash104 2006

[44] P S J Russell ldquoPhotonic-crystal fibersrdquo Journal of LightwaveTechnology vol 24 no 12 pp 4729ndash4749 2006


[45] K Hansen and H Imam ldquoPhotonic crystal fiberrdquo Optik ampPhotonik vol 5 no 2 pp 37ndash41 2010

[46] Z Z Gu H Xu P Wu C Zhu and A Elbaz ldquoPhotonic crystalfor gas sensingrdquo Journal of Materials Chemistry C 2013

[47] Z Cai Y J Liu J Teng and X Lu ldquoFabrication of large domaincrack-free colloidal crystal heterostructures with superpositionbandgaps using hydrophobic polystyrene spheresrdquoACS AppliedMaterials amp Interfaces vol 4 no 10 pp 5562ndash5569 2012

[48] H Huang J Chen Y Yu Z Shi H Mohwald and GZhang ldquoControlled gradient colloidal photonic crystals andtheir optical propertiesrdquo Colloids and Surfaces A vol 428 pp9ndash17 2013

[49] Y Li Z Sun J Zhang et al ldquoPolystyreneTiO2

core-shellmicrosphere colloidal crystals and nonspherical macro-porousmaterialsrdquo Journal of Colloid and Interface Science vol 325 no2 pp 567ndash572 2008

[50] J H Moon G R Yi and S M Yang ldquoFabrication of hollowcolloidal crystal cylinders and their inverted polymeric repli-casrdquo Journal of Colloid and Interface Science vol 287 no 1 pp173ndash177 2005

[51] O Kalinina and E Kumacheva ldquoPolymeric nanocompositematerial with a periodic structurerdquo Chemistry of Materials vol13 no 1 pp 35ndash38 2001

[52] G Cao and C J Brinker Annual Review of Nano ResearchWorld Scientific 2006

[53] M Lanata M Cherchi A Zappettini S M Pietralungaand M Martinelli ldquoTitania inverse opals for infrared opticalapplicationsrdquo Optical Materials vol 17 no 1-2 pp 11ndash14 2001

[54] C Lu C Guan Y Liu Y Cheng and B Yang ldquoPbSpolymernanocomposite optical materials with high refractive indexrdquoChemistry of Materials vol 17 no 9 pp 2448ndash2454 2005

[55] T Huang Q Zhao J Xiao and L Qi ldquoControllable self-assembly of pbs nanostars into ordered structures close-packedarrays and patterned arraysrdquo ACS Nano vol 4 no 8 pp 4707ndash4716 2010

[56] S W Choi J Xie and Y Xia ldquoChitosan-based inverse opalsthree-dimensional scaffolds with uniform pore structures forcell culturerdquo Advanced Materials vol 21 no 29 pp 2997ndash30012009

[57] K Lee and S A Asher ldquoPhotonic crystal chemical sensors pHand ionic strengthrdquo Journal of the American Chemical Societyvol 122 no 39 pp 9534ndash9537 2000

[58] J Ballato andA James ldquoA ceramic photonic crystal temperaturesensorrdquo Journal of the American Ceramic Society vol 82 no 8pp 2273ndash2275 1999

[59] H Fudouzi and Y Xia ldquoColloidal crystals with tunable colorsand their use as photonic papersrdquo Langmuir vol 19 no 23 pp9653ndash9660 2003

[60] H C Kolb M G Finn and K B Sharpless ldquoClick chemistrydiverse chemical function from a few good reactionsrdquo Ange-wandte Chemie vol 40 no 11 pp 2004ndash2021 2001

[61] S Mandal J M Goddard and D Erickson ldquoA multiplexedoptofluidic biomolecular sensor for lowmass detectionrdquo Lab ona Chip vol 9 no 20 pp 2924ndash2932 2009

[62] C Guo C Zhou N Sai et al ldquoDetection of bisphenol A usingan opal photonic crystal sensorrdquo Sensors and Actuators B vol166-167 pp 17ndash23 2012

[63] X Hu J Huang W Zhang M Li C Tao and G Li ldquoPhotonicionic liquids polymer for naked-eye detection of anionsrdquoAdvanced Materials vol 20 no 21 pp 4074ndash4078 2008

[64] H Mıguez S M Yang N Tetreault and G A Ozin ldquoOrientedfree-standing three-dimensional silicon inverted colloidal pho-tonic crystal microfibersrdquo Advanced Materials vol 14 no 24pp 1805ndash1808 2002

[65] E Rusen A Mocanu and B Marculescu ldquoObtaining ofmonodisperse particles through soap-free and seeded polymer-ization respectively through polymerization in the presence ofC 60rdquo Colloid and Polymer Science vol 288 no 7 pp 769ndash7762010

[66] D Gaillot T Yamashita and C J Summers ldquoPhotonic bandgaps in highly conformal inverse-opal based photonic crystalsrdquoPhysical Review B vol 72 no 20 Article ID 205109 2005

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


AB

A

BA

BACBACBA

Figure 1 Three-dimensional arrays (a) HCP (b) CCP [3]

factor (volume of the colloids related to the volume ofsurroundingmedia) In addition one of themost challengingapplications consists in fabricating photonic crystals with 3Dband gap around 155 120583m representing the wavelength usedin optical fibers [23]

2 Polymeric Photonic Crystals

In order to obtain colloidal crystals the most commonmethods consist in surfactant-free emulsion polymerization[5 24] precipitation polymerization [25 26] dispersionpolymerization [27] and seeded emulsion polymerization[28] The absence of surfactants leads to polymer latex ofhigh purity and at the same time the polymerization param-eters (temperature initiator and monomer concentrationsstirring etc) are facile to control The final monodispersepolymer particles represent a class of materials that can beeasily functionalized on the surface therefore increasing thenumber of possible applications [1]

As it was specified in the previous section colloidal crys-tals represent HCP or CCP structures consisting of colloidalmicrospheres ranging from 100 nm to 1 120583m Depending onthe arrangement parameters the photons are forbidden topropagate inside colloidal crystals in certain directions forspecific wavelengths If the lattice potential is strong enoughthe gap might extend to all possible directions resulting in acomplete band gap [29] This property allows the control ofthe light that interacts with the colloidal crystal

Taking this into account it is easy to realize that one ofthemost important optical properties of the colloidal crystalsconsists in light diffraction according to Braggrsquos law

21 Braggrsquos Law In order to better understand the phe-nomenon that occurs inside a polymer photonic crystal it isnecessary to analyze the path of an incident beam that travelsthrough the crystal planes

The diagram below [30] (Figure 3) explains the pathwaythe beam B which represents the extra distance traveled bybeam A Perpendicular lines (l) lines were drawn to bothrays Following thismethod two right triangles were obtained[30]

The angle marked 120579 also called Braggs angle can becalculated from these triangles as sin 120579 = 119904119889 Therefore theextra distance is 2119904 long or 2119889 sin 120579 long This value is equal

with a number of wavelengths (119899) for a strong beam (Braggrsquoslaw)

119899120582 = 2119889 sin 0 (1)

When the Bragg equation is satisfied the angle formedby the diffracted beam with the crystal plane is equal to theone between by the incident beam and the same crystal planeIn this situation diffraction is similar to a reflection from amirror (Braggs mirror effect) where the angle of incidence isidentical to the angle of reflection [30]

In the case of molecular atomic or ionic crystals theinterplanar spacing 119889 is in the range of A thus having thecapacity of diffracting X-rays In the case of colloidal crystals119889 is in the range of 100 nm which implies the diffractionof light with wavelengths of the same order of magnitude(400ndash800 nm) Therefore the colloidal crystal will diffractlight with wavelengths corresponding to violet-blue-greenand transmit it in the complementary radiation (orange-red)of visible light

22 Braggrsquos Law on Colloidal Crystal The examination ofa colloidal dispersion (Figure 4) during and after solventevaporation allows the observation of iridescence in differentareas of the visible spectrum due to diffraction of the light inaccordance with Braggrsquos law [31]

The optical microscopy shows that the distance betweenthe defaults due to water evaporation is only 150ndash200120583mwhich proves the high quality of the film respectively ofthe obtained opal [32] The crystallization process revealspermanent changes in the color of the colloidal dispersionIn the first step the dispersion is white due to Mie scatteringand 119889 is larger than polymer particles [33] In the second stepthe colloidal dispersion changes its colors as a consequence ofreducing the interplanar distance

Figure 5(a) shows a well-ordered close packed structurewith a triangular arrangement that can be attributed to planes(111) of a CCP system [9 31 34] Moreover the (fast fouriertransform) FFT of the image (Figure 5(b)) displays sharppeaks confirming the existence of long-range crystallineorder

According to Braggrsquos law the change of the angle betweenthe incident radiation and photonic crystal leads to notablechanges of the reflected wavelength respectively of theobserved color (Figure 6) [35 36]

UV-VIS spectra of polymer photonic crystals indicatein many cases sharp peaks which confirm the existence ofhighly ordered structures due to Braggs reflection of periodicarrangement of the polymer particles [37ndash40]

Figure 7(b) represents the reflection spectra of poly-mer colloidal crystals with different size particles (178 nm211 nm 235 nm and 270 nm) corresponding to photograph(Figure 7(a)) [41]

Moreover these materials show structural color changes(Figure 8) under mechanical stress In this case the photoniccrystal film deposited on a plastic plate changed from red togreen as result of themodification of the interplanar distancewhich is thus a change in thewavelength of the diffracted light[37]


(a) (b)


AB

AB

985747985747

120582

d

120579 120579

s


(a)

(b)

(c)





(a)

(b)







(a) (b)


(a)

400 600 800

Refle

ctan

ce (

)

178 nm

211 nm 235 nm

270 nm

Wavelength (nm)

100

80

60

40

20

0

(b)





40302010

001 1 10 100 1000 10000






(a)

Air sphere

(b)




(b)

(c)



AB

C










(a) (b)


















(a) (b)

(c) (d)



Inte

nsity

Wavelength

Opticalprobe

Incidencelight

Reflectionlight






(a)

020

015

010

005550 600 650 700 750

Abso

rban

ce

Wavelength (nm)

WaterNaBrNH4NO3

NaBF4

NaClO4

NH4PF6

LiTf2N

(b)


minus ClO4minus PF6

minus

(c)



Laser emission










120120583m

40120583m

75 120583m 1120583m

(a) (b)

(c) (d)






Acknowledgment



References













































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)


AB

AB

985747985747

120582

d

120579 120579

s


(a)

(b)

(c)





(a)

(b)







(a) (b)


(a)

400 600 800

Refle

ctan

ce (

)

178 nm

211 nm 235 nm

270 nm

Wavelength (nm)

100

80

60

40

20

0

(b)





40302010

001 1 10 100 1000 10000






(a)

Air sphere

(b)




(b)

(c)



AB

C










(a) (b)


















(a) (b)

(c) (d)



Inte

nsity

Wavelength

Opticalprobe

Incidencelight

Reflectionlight






(a)

020

015

010

005550 600 650 700 750

Abso

rban

ce

Wavelength (nm)

WaterNaBrNH4NO3

NaBF4

NaClO4

NH4PF6

LiTf2N

(b)


minus ClO4minus PF6

minus

(c)



Laser emission










120120583m

40120583m

75 120583m 1120583m

(a) (b)

(c) (d)






Acknowledgment



References













































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)


(a)

400 600 800

Refle

ctan

ce (

)

178 nm

211 nm 235 nm

270 nm

Wavelength (nm)

100

80

60

40

20

0

(b)





40302010

001 1 10 100 1000 10000






(a)

Air sphere

(b)




(b)

(c)



AB

C










(a) (b)


















(a) (b)

(c) (d)



Inte

nsity

Wavelength

Opticalprobe

Incidencelight

Reflectionlight






(a)

020

015

010

005550 600 650 700 750

Abso

rban

ce

Wavelength (nm)

WaterNaBrNH4NO3

NaBF4

NaClO4

NH4PF6

LiTf2N

(b)


minus ClO4minus PF6

minus

(c)



Laser emission










120120583m

40120583m

75 120583m 1120583m

(a) (b)

(c) (d)






Acknowledgment



References













































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





(a)

Air sphere

(b)




(b)

(c)



AB

C










(a) (b)


















(a) (b)

(c) (d)



Inte

nsity

Wavelength

Opticalprobe

Incidencelight

Reflectionlight






(a)

020

015

010

005550 600 650 700 750

Abso

rban

ce

Wavelength (nm)

WaterNaBrNH4NO3

NaBF4

NaClO4

NH4PF6

LiTf2N

(b)


minus ClO4minus PF6

minus

(c)



Laser emission










120120583m

40120583m

75 120583m 1120583m

(a) (b)

(c) (d)






Acknowledgment



References













































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)


















(a) (b)

(c) (d)



Inte

nsity

Wavelength

Opticalprobe

Incidencelight

Reflectionlight






(a)

020

015

010

005550 600 650 700 750

Abso

rban

ce

Wavelength (nm)

WaterNaBrNH4NO3

NaBF4

NaClO4

NH4PF6

LiTf2N

(b)


minus ClO4minus PF6

minus

(c)



Laser emission










120120583m

40120583m

75 120583m 1120583m

(a) (b)

(c) (d)






Acknowledgment



References













































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)

(c) (d)



Inte

nsity

Wavelength

Opticalprobe

Incidencelight

Reflectionlight






(a)

020

015

010

005550 600 650 700 750

Abso

rban

ce

Wavelength (nm)

WaterNaBrNH4NO3

NaBF4

NaClO4

NH4PF6

LiTf2N

(b)


minus ClO4minus PF6

minus

(c)



Laser emission










120120583m

40120583m

75 120583m 1120583m

(a) (b)

(c) (d)






Acknowledgment



References













































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a)

020

015

010

005550 600 650 700 750

Abso

rban

ce

Wavelength (nm)

WaterNaBrNH4NO3

NaBF4

NaClO4

NH4PF6

LiTf2N

(b)


minus ClO4minus PF6

minus

(c)



Laser emission










120120583m

40120583m

75 120583m 1120583m

(a) (b)

(c) (d)






Acknowledgment



References













































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




120120583m

40120583m

75 120583m 1120583m

(a) (b)

(c) (d)






Acknowledgment



References













































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials







































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials

