Chapter - II Synthesis and Characterization of Polyaniline...
Transcript of Chapter - II Synthesis and Characterization of Polyaniline...
Chapter - II Synthesis and Characterization of
Polyaniline-Polyvinyl Alcohol-Silver Nanocomposite (PANI-PVA-Ag NC)
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2.1 INTRODUCTION:
Polyaniline (PANI) is a conducting polymer of the semi-flexible rod polymer
family. Although it was discovered over 150 years ago, only recently has polyaniline
captured the attention of the scientific community due to the discovery of its high
electrical conductivity. Amongst the family of conducting polymers, polyaniline is
unique due to its ease of synthesis, environmental stability, and acid/base
doping/dedoping chemistry [1]. However, two major shortcomings of conductive
form of polyaniline are difficult to process, since it is insoluble in common organic
solvents and unstable at melt processing temperatures, that has restricted its
applications and its poor mechanical properties. The shortcomings can be overcome
by preparing polyaniline blends and composites that possess the mechanical
properties of the insulating host matrix and the electrical properties of the
conducting polyaniline. When the host is a polymer, the resulting system is known
as a polymer blend (or polymer composite), but when the host is a non-polymer
material (e.g. metal oxides, silica), it is invariably known as a composite.
The inorganic-organic composite materials are increasingly significant due to
their extraordinary properties. There are several methods to synthesize these
materials, but the most well-known method is the incorporation of inorganic
building blocks in organic polymer matrix. The inorganic-organic composite
materials have received much interest due to the remarkable change in properties
such as mechanical [2], thermal [3-6], electrical [7] and magnetic [8] as compared to
pure organic polymers due to the presence of inorganic moieties in the nano scale.
The applications of metal nanoparticles, usually ranging from 1 to 100 nanometers
(nm), have received considerable interest in the advancement of recent research in
both scientific and technological areas due to their distinctive and unusual physico-
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chemical properties compared with that of bulk materials [9,10]. The synthesis of
metal nanoparticles has received much attention because of their electronic, optical,
magnetic and catalytic properties, which depend on their size and shape [11, 12].
Metal nanoparticles are mainly interesting because they can easily be synthesized
and tailored chemically as well as can suitably be used for device fabrication
[13-16]. The unique properties of nanoparticles are due to the increase in the ratio of
the surface area to volume, and the size of the particles. However, for application in
the field of optoelectronics and electronics, the controlled particle size and their
uniform distribution within the polymer matrix is the key to technology, based on
the nanoparticles in polymers. Moreover, metal nanoparticles show surface plasmon
resonance (SPR) absorption in the UV-visible region. The SPR peak arises as a
result of the combined oscillation of free electrons of the metal nanoparticles in
resonance with the frequency of the light wave that interacts with the metal
nanoparticles due to the small particle size [17]. Basically, SPR absorption peak
occurs in metal nanoparticles only. Hence, the existence of SPR peak is the primary
indication of metal nanoparticles formation. Among the various metal nanoparticles,
noble metal nanoparticles have drawn much attention, due to their superior physical
and chemical properties. Nanoparticles may provide solutions to technological and
environmental challenges in the areas of solar energy conversion, catalysis,
medicine, and water treatment. V.K. Sharma et al. have reported the antimicrobial
property of Ag NPs in water filter and air filter [18]. Pillai et al. [19] demonstrated
that solar cells employing metallic nanoparticles can spectacularly enhance the near
infrared absorption due to the presence of surface plasmon. Nowadays, a lot of
researches have been focused on silver nanoparticles because of their important
scientific and technological applications in colour filters [20, 21], optical switching
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[22], and optical sensors [25, 24]. In addition silver nanoparticles have applications
in catalysis, conductive inks, thick film pastes and adhesives for various electronic
components, in photonics and in photography [25-26].
Recently, a lot of research on nanoparticles dispersed within a polymer
matrix has been carried out, because these materials may have various new
properties which originate from the combination of the properties of the inorganic
components and the polymer. The polymeric matrix provides processability and
flexibility and at the same time inorganic nano sized particles not only improve the
mechanical properties of the host polymer, but also give unique properties which
differ from their bulk materials and atoms [27]. Thus polymer nanocomposite
materials represent a new alternative to conventionally nanoscopic inorganic
materials. Among the conducting polymers polyaniline is one of the most promising
polymers due to its exotic properties, environmental stability, controllable electrical
conductivity, and interesting redox properties associated with the nitrogen atoms in
PANI. Polyvinyl alcohol (PVA) being bio-degradable synthetic polymer is largely
used as fiber, film, pressure-sensitive adhesive, emulsifier, in the paper industry, in
textile sizing and as a modifier of thermosetting resins in plywood manufacture etc.
Polyaniline-metal/metal oxide (PANI-metal/metal oxide) nano composites
reportedly show enhanced sensing, corrosion resistant and catalytic capabilities, as
compared to those of pure PANI [28-30]. In the synthesis of PANI-metal
composites, metal ions are often reduced in the presence of processed PANI. In the
resulting composites, metal nanoparticles are not often effectively dispersed into
the polymer matrix, because metal ions and nanoparticles interact strongly with
the imino groups of the polymer and reduced at the point of contact [31].
Mahesh et al [32] have synthesized Pani-Ag nano composites via interfacial
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polymerization. Radhakrishnan et al [33-34] have synthesized Ag-PVA film by
using PVA as surfactant for stabilization of Ag into the polymer matrix.
Silver nanoparticles are of current importance because of its easy preparation
process and excellent optical, electrical, thermal, catalytic, sensing, and antibacterial
properties. The unique properties of Ag NPs make them ideal for numerous
technological applications such as in the field of catalysis, electronics, photography,
adhesives, optical, biomedical and antimicrobial materials etc. [8-18]. The synthesis
of silver nanoparticles with controlled morphology is essential for uncovering their
specific properties and for achieving their practical applications. However, one
major problem while synthesizing nanocomposite materials derived from the
dispersion of silver nanoparticles in polymer matrices is the aggregation of
nanoparticles. Hence, the synthesis of silver nanoparticles of desired shape and size
with uniform distribution within the polymer matrix remains extremely challenging.
Therefore, in the present research work, we have shown the synthesis of silver
nanoparticles homogeneously dispersed within the (PANI-PVA) polymer matrix
with controlled morphology without aggregation. The one step synthesis of
polyaniline-polyvinyl alcohol-silver (PANI-PVA-Ag) IPN nanocomposite by the in
situ polymerization of aniline in the PVA matrix in the presence of silver nitrate
solution is proved to be a simple and convenient method. Different characterizations
including morphological and spectral properties of the nanocomposite in the solid
state were performed and the results of the study are discussed.
2.2 SYNTHESIS OF POLYANILINE (PANI):
2.2.1 Materials and Method:
All the chemicals and reagents used were of analytical grade. Aniline,
benzene, and methanol was double distilled before use as solvents and monomer and
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hydrochloric acid supplied by SD Fine Chemicals Ltd. were used for the study.
Ammonium persulphate [(NH4)2S2O8] (APS) was used from Qualigens Fine
Chemicals. Double distilled water was used throughout the work.
Polyaniline (PANI) was synthesized by employing chemical oxidative
polymerization method using ammonium persulphate as an oxidizing agent through
established procedure [29].
2.2.2 Experimental Procedure:
0.2 g of aniline was dissolved in 10 ml of organic solvent (C6H6) and 0.1 M
ammonium persulphate (APS) was dissolved in 10 ml of 0.1 M hydrochloric acid
(HCl) at room temperature. The ammonium persulphate solution was then
transferred to aniline solution. Aniline: APS ratio was maintained as 1: 2.5.
Within few minutes after the addition of APS, the solution becomes dark green
colour indicating beginning of the polymerization of aniline. The solution was then
kept overnight so as to complete the polymerization process. The precipitate of
polyaniline (PANI) was then separated by filtration using Whatman No. 42 filter
paper and washed with 1:1 methanol/HCl mixture to remove the unreacted aniline
and acidic impurities. The PANI thus obtained was dried in vacuum oven at room
temperature (25o C ± 1o C) for 36 hours. This dried product was then used for
structural characterization and thermal studies.
2.3 CHARACTERIZATION TECHNIQUES:
The Fourier transform infrared (FTIR) spectrum of the sample was recorded
on a Perkin-Elmer FTIR (Model No.1000) in the range 4,000-400 cm-1 and at a
resolution of 4 cm-1. UV-Visible absorption spectrum of the polymer solution was
recorded over the wave length range of 200-800 nm using double beam UV-Visible
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spectrophotometer-UV5704SS (Electronics Corporation of India Limited).
The powder X-ray diffraction (XRD) patterns were recorded on Ultima IV X-ray
diffractometer using Cu Kβ radiation (1.54 Ǻ) at 40 kV and 30 mA. Thermo
gravimetric analysis (TGA) and differential scanning colorimetric (DSC) analysis of
PANI was carried out in the temperature range 30-4500 C in a LINSEIS STA PT
1600 system thermal analyzer with a heating rate of 10o C/min under nitrogen
atmosphere at a flow rate of 100 ml/min. Scanning electron microscope (SEM)
images of the polymer were taken on the Leica instrument (Model No.440) operated
at 20 kV.
2.4 RESULT AND DISCUSSION:
2.4.1 Ultraviolet-Visible (UV-Vis) Spectroscopy:
The UV-visible spectrum of pure PANI (Figure 2.1) shows a shoulder at
320 nm, a sharp intense peak at 420 nm and a groove at 550 nm with an extended
free carrier tail characteristic of an extended coil confirm the increasing absorbance
in the range of 850 – 1,100 nm [32]. The shoulder at 320 nm corresponds to the
π – π* transitions of the benzenoid rings, while the sharp intense peak at 420 nm is
assigned to the localized polarons transition which are characteristics of the
protonated PANI [35-36]. A weak peak at 550 nm can be attributed to the n – π*
transitions of the benzenoid ring together with extended tail representing the
conducting form of polyaniline because the free carrier tail in the IR region is the
characteristics of metallic conductive materials [32].
2.4.2 Fourier Transform Infrared Spectroscopy (FTIR):
Figure 2.2 shows FTIR spectrum of PANI. In the spectrum of PANI
characteristic bands are observed at 3735, 1564, 1496, 1299, 1147, 877, 811, 678,
621 and 503 cm-1. A small peak at 3735 cm-1 is assigned to the free N-H
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stretching vibrations of an amino group. The high frequency strong bands at
1564 and 1496 cm-1 are due to the presence of the quinoid ring and the benzenoid
ring respectively [37]. The intense peak at 1299 cm-1 in the spectrum corresponds to
the C–N stretching vibrations of the secondary aromatic amine [38]. A very strong
and broad band at 1147 cm-1 has been assigned to the B – NH+ = Q vibration,
indicating that the PANI is conductive and is in the form of emeraldine salt [32].
The remaining peaks at 877, 811 and 503 cm-1 corresponds to bending vibrations of
C – H out of plane, in-plane and C – Cl stretching vibrations respectively [39].
2.4.3 X-ray Diffraction (XRD):
The crystallinity and chain packing of the synthesized polyaniline was
studied by X-ray diffraction analysis. Figure 2.3 shows the XRD patterns of virgin
PANI. The figure shows the broad peak at 2θ value of 25.3o, which is characteristic
peak of PANI [40] and is ascribed to the periodicity in parallel and perpendicular
directions of the polyaniline chain [41, 42]. It is characteristics of van der Waals
distances between stacks of phenylene rings (polyaniline rings) [43-45].
2.4.4 Scanning Electron Microscopy (SEM):
The SEM image of pure PANI is shown in Figure 2.4. The figure shows the
individual ultrafine PANI particles uniformly packed. The particles are rod shaped
with uniform particle size of about 100 nm to 200 nm. It is reported that PANI
synthesized from other synthetic routes possess irregular morphology with high
heterogeneity in chain dimensions [46]. A uniform morphology and chemical
homogeneity is observed in the present case.
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2.4.5 Thermal Studies:
2.4.5 a) Thermogravimetric analysis (TGA):
Thermal stability of the synthesized PANI was studied by simultaneous thermo
gravimetric analysis (TGA) and differential scanning calorimetry (DSC) measurements
under a dynamic flow of nitrogen gas at a flow rate 100 ml/min with a heating rate of
10oC/min. the TGA/DSC trace of pure PANI is shown in Figure 2.5(a). The following
features are observed with the increasing temperature. The weight loss of 12% occurs
within the temperature range of 30-110oC owing to the release of moisture, HCl and
other volatile matter associated during the synthesis of PANI. No considerable change
in weight loss is observed from 110-290o C. This indicates the thermal stability of the
polymer. Thereafter a continuous loss is noticed in the temperature range from
290-450oC showing a maximum of 61% leaving ~27% residue. This weight loss is
attributed to the decomposition as well as degradation of the polymer as also reported in
our earlier work and by other authors [32, 38, and 47].
2.4.5 b) Differential Scanning Calorimetry (DSC):
In the DSC trace, Figure 2.5 (b) PANI shows a weak endotherm around
80-100o C due to release of dopant, moisture and other volatile matter. The trace is
then followed by a broad endotherm around 270-290o C relating to starting of
decomposition at high temperatures. PANI completely decomposes above 400o C,
showing a broad exothermic peak. PANI shows an irregular weight loss and absence
of a clear dehydration step when synthesized employing chemical oxidation
routes [48]. A clear dehydration and loss of volatiles step followed with a slow and
steady weight loss for decomposition is an important feature, which helps in
employing this method to synthesize functionalized PANI for specific applications.
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2.5 SYNTHESIS OF PANI-PVA-Ag IPN NANOCOMPOSITE:
2.5.1 Materials and Methods:
All chemicals and reagents used were of analytical grade. Aniline and
methanol was double distilled before use as monomer and solvent and hydrochloric
acid supplied by SD Fine Chemicals Ltd. were used for the study. Polyvinyl alcohol
(PVA), ammonium per sulphate (APS) and silver nitrate (AgNO3) were used from
Qualigens Fine Chemicals. Double distilled water was used throughout the work of
the study. Polyaniline-polyvinyl alcohol-silver (PANI-PVA-Ag) IPN nanocomposite
was synthesized by employing chemical oxidation polymerization method using
ammonium persulphate as an oxidizing agent as explained.
2.5.2 Experimental Procedure:
The synthesis of polyaniline-silver (PANI-Ag) and polyaniline-gold (PANI-Au)
nano composites by interfacial polymerization method using ammonium persulphate as
an oxidizing agent was reported in our earlier research work by Mahesh et al.
PANI-PVA-Ag nanocomposite was synthesized by chemical oxidative
polymerization of aniline in the PVA matrix in the presence of silver nitrate
solution. Freshly distilled 0.2 M aniline was polymerized in the aqueous solution of
PVA (0.2 g in 10 ml H2O) in the presence 1x10-3 M AgNO3 solution by the usual
technique of chemical oxidative polymerization using aqueous acidic solution of
ammonium persulphate with constant stirring. Here aqueous acidic solution of
ammonium persulphate (APS) acts as an oxidizing agent. Aniline: APS mole ratio
was maintained 1:2.5. After 5 min. dark reddish brown color was formed indicating
the formation of the silver nano-particles in the solution. The reaction mixture was
kept undisturbed for 18 hours so as to complete the reaction. The precipitate was
then separated by centrifuging and washed with 1:1 methanol/HCl mixture to
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remove the unreacted aniline and acidic impurities. The nano composite thus
obtained was dried in vacuum oven at 40o C for 36 hours. This dried polymer-metal
nanocomposite sample was then used for structural characterization and thermal
studies.
2.5.3 Characterization Techniques:
The Fourier transform infrared (FTIR) spectrum of the sample was recorded
on a Perkin-Elmer FTIR (Model No.1000) in the range 4,000-400 cm-1 and at a
resolution of 4 cm-1. UV-Visible absorption spectrum of the composite was recorded
over the wave length range of 200-800 nm using double beam UV-Visible
spectrophotometer-UV5704SS (Electronics Corporation of India Limited).
The powder X-ray diffraction (XRD) patterns were recorded on Ultima IV X-ray
diffractometer using Cu Kβ radiation (1.54 Ǻ) at 40 kV and 30 mA. Thermo
gravimetric analysis (TGA) and differential scanning colorimetric (DSC) analysis of
PANI-PVA and PANI-PVA-AgNP composite were carried out in the temperature
range 30-450o C in a LINSEIS STA PT 1600 system thermal analyzer with a heating
rate of 10o C/min under nitrogen atmosphere at a flow rate 100 ml/min. Scanning
electron microscope (SEM) images of the composite were taken on the Leica
instrument (Model No.440) operated at 20 kV.
2.6 RESULTS AND DISCUSSION:
2.6.1 UV-Visible Spectroscopy:
The UV-visible spectrum of PANI-PVA-Ag nanocomposite in the aqueous
phase is shown in Figure 2.6. The absorption spectrum of PANI-PVA-Ag
nanocomposite shows five absorption bands. A broad band appears at 326.5 nm,
sharp intense peaks at 419.5, 443.5 and 448.0 nm and a medium peak 552.0 nm.
A broad band at 326.5 nm corresponds to the π-π* transition of the benzenoid ring of
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the PANI. The absorption peaks at 419.5 and 552.0 nm are assigned to the polaron-
π* and n-π* transitions of the protonated form of PANI. The peak owing to
polaron/bipolaron transition is also observed at 443.5 nm with little blue shift due to
the presence of silver nanoparticles. The sharp intense peak at 448.0 nm is assigned
to the surface plasmon resonance (SPR) absorption of the electrons in the
conduction bands of silver which confirms the formation of nano sized silver
particles. Since surface plasmon bands appearing in the visible region are
characteristics of the noble metal nanoparticles [32]. The result is consistent with
previous reports [49].
2.6.2 Fourier Transform Infrared (FTIR) spectroscopy:
The PANI-PVA-Ag nanocomposite was further characterized by infrared
spectroscopy. Figure 2.7(a, b) shows the FTIR spectrum of pure PVA and PANI-
PVA-Ag NC. The infra red spectrum of PVA Figure 2.7 (a) shows the
characteristic bands at 3296, 2940, 1714, 1423, 1252, 1087 and 832 cm-1. The very
strong broad band at 3296 cm-1 can be assigned to O – H stretching due to the strong
hydrogen bonding of intramolecular and intermolecular type [50]. The C – H
stretching and bending vibrations are observed at 2940 and 1423 cm-1. The small
peak at 1374 cm-1 is due to – CH2 – wagging and intense peak at 1087 cm-1 is due to
C – O stretching vibrations. The peaks at 1714 and 1252 cm-1 are due to C = O and
C – O – C bonds of the non hydrolyzed vinyl acetate group of the polyvinyl acetate.
The IR spectrum of PANI-PVA-Ag NC Figure 2.7 (b) exhibits all the peaks
corresponding to PANI and PVA network. A shoulder at 3359 and 2922 cm-1
correspond to free N –- H stretching vibrations of an amino group of PANI and
C – H stretching vibrations of PVA segment respectively. The very strong broad
band of PVA at 3296 cm-1 due to O – H stretching vibrations is splitted into more
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peaks. The intense peak at 3264 cm-1 is assigned to O – H stretching due to the
strong hydrogen bonding of intramolecular and intermolecular type [50]. This peak
is shifted to 32 cm-1 lower frequency than in the PVA spectrum. The bands at
3197 and 3050 cm-1 are due to the presence of hydrogen bonding between the PANI
and PVA networks [51]. The presence of quinoid (Q) ring stretching vibrations at
1580 cm-1 and benzenoid (B) ring stretching vibrations at 1505 cm-1 are typical
features of a semi-quinoid structure of emeraldine salt form of PANI. The bands at
1303 and 1299 cm-1 are attributed to C–N deformation modes and stretching
vibrations of aromatic amine. The absorption peaks at 1444 and 1207 cm-1 are due to
C-H bending and C-H waging vibrations respectively. The peaks at 905, 860 and
486 cm-1 corresponds to bending vibrations of C – H out of plane, in-plane and
C – Cl stretching vibrations [39]. The medium peaks at 739 and 694 cm-1 are
attributed to the out of plane deformation of C – H aromatic ring and the C – H
stretching vibrations respectively. The absence of the strong and broad band at
1147 cm-1 due to protonated chain (B – NH+ = Q) vibration of the conductive
emeraldine salt form of PANI in the composite is noteworthy [32]. The band due to
protonated chain vibration of the conductive emeraldine salt form of PANI is
weakened when silver nanoparticles are incorporated in the polymer matrix and is
shifted to 1173 cm-1. For the reason that Ag+ is reduced to Ago and the amine
(–NH–) group of the polyaniline chain is oxidized to imine (–N=) group [32].
Additional frequencies and shift in frequencies are found in nanocomposite
spectrum compared to PVA indicating the formation of nano composite.
2.6.3 X-ray Diffraction Studies:
The crystallinity and chain packing of the synthesized polymer and its
composite were studied by XRD analysis. Figure 2.8 (a, b) shows the X-ray
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diffraction (XRD) pattern of pure PVA and PANI-PVA-Ag nanocomposite.
The X-ray diffraction pattern of PVA (Figure 2.8 a) shows an intense diffraction
peak at around 2Ѳ = 20o indicating the presence of a typical semi crystalline
structure. The X ray diffraction pattern of PANI-PVA-Ag composite (Figure 2.8 b)
exhibits intense diffraction peaks at 2Ѳ = 38.38o, 45.18o and 65.3o with
corresponding diffraction signals to (111), (200) and (220) planes of silver,
respectively that match with the JCPDS pattern of Ag nanoparticles, JCPDS File
No. 04-0783 indicating the presence of silver nanoparticles in the composite.
As reported by Desong Wang et. al the reflection peaks can be indexed to face-
centered cubic silver [52]. Thus, the XRD spectrum confirms the crystalline
structure of silver nanoparticles with a face-centered cubic structure. From this we
can infer that the crystallinity of the PANI-PVA-Ag nanocomposite is mainly due to
silver nanoparticles rather than PVA. The size of the silver nanoparticles as
calculated from XRD data is 34. 926 nm.
2.6.4 Morphology Studies:
Scanning Electron Microscopy:
The SEM images of PANI-PVA-Ag nanocomposite at low and high
resolution are shown in Figure 2.9 (a, b). The SEM images show that the Ag
nanoparticles are homogeneously distributed within the PANI-PVA IPN matrix. As
shown in SEM image (Figure 2.9), the silver nanoparticles (Ag NP) are well
embedded in the PANI-PVA IPN composite matrix due to strong affinity of silver
for nitrogen of the polyaniline. It can also be noticed that the globular shaped Ag
nanoparticles are clearly mono dispersed. An interpenetrating network structure of
silver nano particles within the PANI-PVA matrix is proposed with the schematic
sketch as shown in Figure 2.10. Thus it proves that the PANI-PVA polymer
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composite matrix is an excellent host matrix to avoid the aggregation of silver
nanoparticles and is helpful for encapsulation of silver nanoparticles acting as a
good capping agent and providing chemical and environmental stability as well.
The size of the silver particles is < 50 nm and is spherical in shape. The SEM
morphology shows that Ag nanoparticles possess the same particle size.
2.6.5 Thermal Studies:
Thermogravimetric Analysis (TGA):
Thermal stability of the synthesized IPNs was studied employing
simultaneously TGA and DSC techniques. Figure 2.11 (a, b) shows the thermal
plots of PANI-PVA and PANI-PVA-Ag nanocomposite. The TGA curve of
PANI-PVA composite Figure 2.11 (a) shows three steps due to release of dopant
over 30-100o C, moisture and bound water in the range 180-240o C, and degradation
of the components over 400o C. The TGA plot of the for PANI-PVA-Ag IPN
nanocomposite Figure 2.11 (b) shows two step decomposition patterns. The first
weight loss of 21% occurs in the range of room temperature to 300o C which is
attributed to the release of moisture, dopant, and degradation of the PVA molecule
to form low molecular weight fragments. No considerable change in weight loss is
observed from 300 to 540o C, which indicates the increase in the thermal stability of
the polymer-metal nanocomposite due to the presence of silver nanoparticles.
The continuous weight loss is noticed in the second step which starts at 540o C and
continues up to 700o C. This weight loss is due to the decomposition of the
nanocomposite. Thus, silver nano particles may act as stabilizer for the IPN so that
the decomposition temperature is increased for PANI-PVA-Ag IPN when compared
without silver for PANI-PVA IPN (discussed in Chapter – III).
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Differential Scanning Calorimetry (DSC):
The DSC curves of PANI-PVA composite Figure 2.11 (a) shows one broad
endotherm around 200o C, due to the fact that some of the vinyl segments were
subject to dehydration to form a conjugated unsaturated structure. The moisture and
dopant release endotherm is disappeared as a result of the formation of the hydrogen
bonding between PANI and PVA components. Ultimately over 400o C both the
components of the composite decompose to volatile products. The DSC profile of
PANI-PVA-Ag composite Figure 2.11 (b) shows a broad exotherm at 140o C which
is mainly attributed to the crystallization of silver nanoparticles, an endotherm
around 270o C relating to morphological changes at high temperatures and a broad
exothermic peak at 630o C due to the decomposition of IPN in the temperature
region of 540 to 700o C. The increased thermal stability of the polymer composite
may be attributed to the formation of interpenetrating polymer network embedded
with silver nanoparticles. It is observed from thermal studies that residue exists for
PANI-PVA IPN Figure 2.11 (a) but in case of PANI-PVA-Ag Figure 2.11 (b)
residue goes to 0 % above 800o C.
2.7 CONCLUSION:
It has been concluded with the synthesis of PANI-PVA-Ag IPN
nanocomposite that the PANI-PVA polymer IPN matrix is helpful in avoiding the
aggregation of globular shapes silver nanoparticles with homogeneous distribution
of the particles. Thermal study of the nanocomposite shows that there is increase in
the thermal stability of the polymer composite due to the presence of silver
nanoparticles and catalytic effect is observed after dehydration. This indicates that,
catalytic decomposition during thermal analysis of the PANI-PVA-Ag
nanocomposite.
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Figure 2.1: UV-visible spectrum of Polyaniline
Figure 2.2: FT-IR Spectrum of Polyaniline
80
Figure 2.3: XRD pattern of Polyaniline
Figure 2.4: SEM image of Polyaniline
81
Figure 2.5 (a): TGA trace of Polyaniline
Figure 2.5 (b): DSC trace of Polyaniline
82
Figure 2.6: UV-Visible Spectrum of PANI-PVA-Ag nanocomposite
Figure 2.7 (a): -FT-IR spectrum of PVA
83
Figure 2.7 (b): FT-IR Spectrum of PANI-PVA-Ag Nanocomposite
Figure 2.8 (a): XRD pattern of PVA
84
Figure 2.8 (b): XRD pattern of PANI-PVA-Ag nanocomposite
Figure 2.9 (a): SEM image of PANI-PVA-Ag nanocomposite at low resolution
85
Figure 2.9 (b): SEM image of PANI-PVA-Ag nanocomposite at high resolution
Figure 2.10: Structural representation of PANI-PVA-Ag interpenetrating network (IPN)
86
Figure 2.11 (a): TGA/DSC trace of PANI-PVA composite
Figure 2.11 (b): TGA/DSC trace of PANI-PVA-Ag Nanocomposite
87