pmma-pani (acid doped) blends -...

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Chapter-3

PMMA-PAni (acid doped) Blends

As already discussed in Chapter 1 (Section-1.6), the present study

highlights the optical, electrical and structural response of Poly(methyl

methacrylate) (PMMA) on blending with Polyaniline (PAni) having

doping of acids and metal salts. In the present chapter, after

discussing the properties of synthesized dodecyl benzene sulfonic acid

(DBSA) and camphor sulfonic acid (CSA) doped PAni, modifications in

the optical, electrical and structural behaviour of PMMA on blending it

with the as prepared PAni at different concentrations is presented.

Finally, the observed changes in the optical and electrical behaviour

are tried to be understood in terms of the induced structural changes

revealed through FTIR and Raman spectroscopic techniques.

3.1 ACIDS (DBSA AND CSA) DOPED POLYANILINE

Polyaniline doped with DBSA and CSA was synthesized by following

the procedure as already discussed in Chapter 2, Section-2.2. In order

to confirm the nature of as prepared PAni powders, the same were

subjected to UV-Visible absorption, FTIR and Raman spectroscopic

analysis.

Ph.D. Thesis: A.K. Tomar-2012

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3.1.1 UV-Visible Absorption Studies

The prepared DBSA and CSA doped PAni powders were first

dissolved in Chloroform and then subjected to UV-Visible spectroscopy.

Figure 3.1 presents the recorded absorption spectra for DBSA and CSA

doped PAni. These spectra clearly indicate that PAni doped with DBSA

shows an absorption peak at the wavelength ~350 nm while similar

peak at ~366 nm for PAni doped with CSA has been observed. These

absorption peaks correspond to the π → π* transition of electrons in

benzenoid ring present in the PAni structure [Masters et al. 1991;

Ikkala et al. 1995; Dhawan et al. 2003; Araujo et al. 2005; Malmonge

et al. 2006; Ebrahim et al. 2009; Wallace et al. 2009].

Figure 3.1: UV-Visible absorption spectra of DBSA and CSA doped PAni

The absorption peak at ~435 nm for PAni.DBSA, and at ~458 nm

for PAni.CSA, is attributed to the characteristic absorption of the salt

form of PAni. Further, the observed broad absorption bands centred

around 820 nm and 809 nm in DBSA and CSA doped PAni, respectively

are assigned to the benzenoid to quinoid excitonic transitions, i.e.

polarons band transitions, which are responsible for the conducting

Chapter-3: PMMA-PAni (acid doped) Blends

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nature of these acid doped PAni salts [Dhawan et al. 2003; Araujo et

al. 2005; Malmonge et al. 2006; Ebrahim et al. 2009; Wallace et al.

2009].

3.1.2 FTIR Spectroscopy

In order to confirm the chemical nature of synthesized PAni doped

with DBSA and CSA, the same were characterized through FTIR

spectroscopy. Figure 3.2 shows the FTIR spectra of PAni.DBSA

(spectrum ‘a’) and PAni.CSA (spectrum ‘b’).

Figure 3.2: FTIR spectra of PAni doped with (a) DBSA and (b) CSA

The broad absorption band observed at wavenumbers higher than

2000 cm–1 in these spectra is due to the absorption of free charge-

carriers in the protonated (doped) PAni, which confirms its conducting

form (emeraldine salt) [Epstein et al. 1986; Neoh et al. 1993; Ping

1996; Trchova and Stejskal 2011]. The strong peaks at 1574 and

1488 cm–1 in PAni.DBSA, and at same wavenumbers in PAni.CSA, are

due to quinoid (Q) and benzenoid (B) ring-stretching vibrations,

respectively. The absorption band at 1303 cm–1 in PAni.DBSA


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(~1307 cm-1 in PAni.CSA) corresponds to π-electron delocalization

induced in the polymer on doping [Kim et al. 1988; Cao et al. 1989,

Masters et al. 1991; Ping 1996; Bhat et al. 2002; Dhawan et al. 2003;

Malmonge et al. 2006; Trchova and Stejskal 2011]. The characteristic

bands observed at 1265 cm–1 and 1257 cm-1 for PAni doped with DBSA

and CSA, respectively correspond to C–N+• stretching vibration in the

polaron structure [Boyer et al. 2000; Ameen et al. 2008; Afjal et al.

2009, 2010; Trchova and Stejskal 2011], which again confirm the

conducting nature of PAni after doping.

The band exhibited at 1126 cm–1 in PAni.DBSA and the shoulder at

1149 cm-1 in PAni.CSA are assigned to the vibration mode of –NH+=

structure, and associated with the vibrations of the charged polymer

units Q=NH+−B or B−NH+•−B [Boyer et al. 1998; Kang et al. 1998;

Socrates 2001; Trchova and Stejskal 2011]. This indicates the

existence of positive charges on the chain and the distribution of the

dihedral (torsion) angle between the quinoid and benzenoid rings. This

band is related to the high degree of electron delocalization in PAni, as

well as to a strong interchain NH+...N hydrogen bonding [Colomban et

al. 1994; Hasik et al. 2002; Trchova and Stejskal 2011]. The

asymmetric SO3 stretching vibration in the hydrogen sulphate counter

ion (present in DBSA and CSA) can also contribute to this band. The

peak observed at 1056 cm–1 for PAni.DBSA and the band centred at

1064 cm-1 for PAni.CSA are attributed to the symmetric SO3 stretching

in the hydrogen sulphate counter ion. The band at 879 cm–1 in the

spectrum of the PAni.CSA has been attributed to the HSO4– counter

ion. The sharp bands at 817 cm–1 in PAni.DBSA and 794 cm-1 in

PAni.CSA spectra are due to the C–H out-of-plane bending vibrations

of two adjacent hydrogen atoms on a disubstituted benzene ring

[Bellamy 1962; Vien et al. 1991; Boyer et al. 1998; Kang et al. 1998;

Socrates 2001; Trchova and Stejskal 2011]. This confirms the

dominating para-coupling of constitutional units in PAni chains.

Thus, the FTIR analysis of DBSA and CSA doped PAni, as discussed

above, confirms the formation of PAni in its emeraldine salt form.


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3.1.3 Raman Spectroscopy

Figure 3.3 presents the recorded Raman spectra of PAni.DBSA and

PAni.CSA in powder form. The intense peaks at 1622 cm−1 for DBSA

doped PAni (spectrum ‘a’) and at 1604 cm-1 for CSA doped PAni

(spectrum ‘b’) correspond to quinoid C=C stretching mode of PAni

chains. The absorption peaks at 1528 cm−1 for PAni.DBSA and at

1521 cm−1 for PAni.CSA are assigned to the N–H bending deformation

band of protonated amine and show the angular deformation of N–H

group.

Figure 3.3: Raman spectra of PAni doped with (a) DBSA and (b) CSA

The band positioned at 1363 cm−1 in PAni.DBSA, while at 1340 cm-1

for PAni.CSA, is the signature of the C–C stretching mode of quinoid

ring present in PAni backbone. The small absorption band at 1247 cm−1

for PAni.DBSA (~1240 cm-1 for PAni.CSA) is attributed to the

delocalized polaronic charge carriers, which confirms that PAni is in its

doped form. The peak located at 1188 cm−1 for PAni.DBSA (~1185 cm-1

for PAni.CSA) is assigned to the out of plane C–H bending in the chain.


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The peak observed at 880 cm-1 in PAni.DBSA (~882 cm-1 in PAni.CSA)

is assigned to O-C(O)-O stretching mode in the PAni chain. The peak

positioned at 589 cm-1 in PAni.CSA spectrum is assigned to the

formation of cross-linking between the PAni chains. The other small

peaks or bands are also in accordance with the characteristic nature of

doped PAni. Thus, Raman analysis of DBSA and CSA doped PAni

confirms the formation of emeraldine salt form of PAni [Ward and Mi

1999; Tagowska et al. 2004; Silva et al. 2005; Lu et al. 2009; Kumar

et al. 2010; Shakoor and Rizvi 2010; Tomar et al. 2012], in line with

FTIR analysis.

As discussed above, the presence of polaron absorption

band around 820 nm in UV-Visible spectrum, absorption at

around 1303, 1265 and 1126 cm-1 in FTIR spectrum and peak at

~1240 cm-1 in Raman spectrum of PAni.DBSA, and

corresponding peaks/bands in PAni.CSA, confirm the presence

of charge carriers (polarons in the present case) in the

synthesized PAni, which are responsible for conducting nature

of PAni.

After confirming the conducting form of DBSA and CSA doped PAni;

in the next section, the results of conductivity measurements of

synthesized PAni are presented.

3.1.4 Conductivity Measurements

For the determination of conductivity, the V-I measurements of

DBSA and CSA doped PAni (in pellet form) have been carried out using

two probe method and the results are presented in figure 3.4. This

figure clearly indicates the linear increase in current with applied

voltage and shows the Ohmic behaviour for both DBSA and CSA doped

PAni. From the V-I data, the conductivity was determined and found to

be 5.69 S/cm and 4.93 S/cm for PAni doped with DBSA and CSA,

respectively. These values of conductivity lie in the range of conductors

[Blythe 1979, 1984; Epstein 1997; Kohlman et al. 1997; Sze 2004;


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Jain et al. 2007]. Thus, it can be inferred that the prepared DBSA and

CSA doped PAni are conducting in nature.

Figure 3.4: V-I characteristics of DBSA and CSA doped PAni

After confirming the conducting nature of as prepared acids doped

PAni, the same were mixed with PMMA at different concentrations

(weight %) through sol-gel process and finally, free standing PMMA-

PAni composite films were prepared using solution casting method.

Such prepared films were subjected to various characterization

techniques to study the induced changes in optical, electrical and

structural properties of PMMA on blending with acids doped PAni at

different concentrations. The results are presented in the following

sections.

3.2 PMMA-PANI.DBSA BLENDS

In order to study the induced changes in optical behaviour of PMMA

after blending with DBSA doped PAni at different concentrations, the

blended films were subjected to the UV-Visible-NIR absorption

spectroscopy. The structural rearrangements caused due to


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incorporation of PAni.DBSA in PMMA were revealed through FTIR and

Raman spectroscopic techniques. To study the variation in electrical

behaviour of these blends, V-I and dielectric measurements were

carried out.

3.2.1 UV-Visible-NIR Absorption Studies

Figure 3.5 presents the UV-visible-NIR absorption spectra of PMMA

and its blends with varying concentration (0.4, 1.0, 2.0, 6.0 and 10.0;

% by weight) of PAni.DBSA. It is evident from curve ‘a’ of this figure

that PMMA exhibits two absorption peaks in UV-region, i.e. at 298 nm

and 340 nm, and remains almost transparent in complete visible

region, confirming its characteristic behaviour [Jin et al. 1992].

Figure 3.5: UV-Visible-NIR absorption spectra of PMMA and PMMA-

PAni.DBSA blends

After doping PMMA with 0.4% by weight of PAni.DBSA (curve ‘b’),

two new bands at around 440 nm and 799 nm start emerging. These

bands correspond to π → π* transitions and polaron band transitions,

respectively in PAni.DBSA [Ong et al. 1997; Mamunya et al. 2002;

Laska 2004; Ebrahim et al. 2009; Wallace et al. 2009]. The intensity


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of these new bands has been found to increase consistently with

increase in PAni.DBSA concentration in PMMA (curve ‘c’ to ‘f’). Further,

the merging of the observed characteristic peaks of PMMA with band at

440 nm at higher concentrations (2 weight % and above) of

PAni.DBSA indicates the formation of chemical conjugation of

PAni.DBSA particles with PMMA chains. The same is also confirmed

through FTIR and Raman spectroscopic analysis presented in the

proceeding sections.

It is also clearly observable from this figure that there is a

continuous shift in the absorption edge corresponding to PMMA

towards the longer wavelengths with increasing concentration of

PAni.DBSA in PMMA. The observed shift in absorption edge can be

explained in terms of the formation of new energy levels within the

band gap of PMMA on the addition of PAni.DBSA.

Determination of Optical Energy Gap

In order to determine the values of optical energy gap of PMMA

and its blends with varying concentration of PAni.DBSA, the values of

(αhυ)1/2 as a function of photon energy (hυ) corresponding to the

fundamental absorption edge in the respective UV-Visible absorption

spectra (figure 3.5), have been plotted in the light of Tauc’s relation

[Tauc 1974; Fink 2004; Mighad and Zidan 2006; Kumar et al. 2011].

The linear fitted lines in these plots have been extrapolated and their

intercepts on hυ axis (figure 3.6) provide the values of optical energy

gap. The values of optical energy gap, so obtained, for pure PMMA

and its blends are presented in table-3.1.

It is clearly observable from table-3.1 that the value of optical

energy gap, which comes out to be 2.72 eV for pure PMMA, has been

found to decrease continuously with increase in the concentration of

PAni.DBSA in PMMA and finally, attains a value of 1.81 eV at 10%

concentration (by weight) of PAni.DBSA in PMMA. Such a reduction in

the values of optical energy gap may be explained in terms of the

change in the structure of PMMA due to the formation of some kinds of

bonding between the embedded PAni.DBSA and PMMA chains.


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Figure 3.6: Plots for the determination of optical energy gap for PMMA

and PMMA-PAni.DBSA blends

Table-3.1: Optical energy gap values for PMMA and PMMA-

PAni.DBSA blends

Sample Optical Energy Gap (eV)

Pure PMMA 2.72 ± 0.02

PMMA+0.4% PAni.DBSA 2.45 ± 0.01

PMMA+1% PAni.DBSA 2.20 ± 0.01





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This may, in turn, results in the formation of localized states

between the HOMO and LUMO bands of PMMA, which modifies their

extended electronic states, thus, contributing towards the formation of

charge transfer complexes (CTCs) [Devi et al. 2002; Mamunya et al.

2002; Laska 2004; Ebrahim et al. 2009]. These CTCs are responsible

for the feasibility of lower energy transitions leading to the observed

change in optical energy gap.

3.2.2 FTIR Spectroscopic Studies

In order to reveal the induced structural changes in PMMA after

blending it with PAni.DBSA at different concentrations, FTIR spectra of

PMMA and its blends have been recorded and are presented in

figure 3.7. This figure clearly indicates that in pure PMMA

(spectrum ‘a’), the following bands/peaks are observed.

Figure 3.7: FTIR spectra of PMMA and PMMA-PAni.DBSA blends

The bands appeared at 3200-3600 cm-1 and 2700-3100 cm-1 may

be assigned to the stretching vibration modes of O-H and C-H bonds,

respectively present in the methyl group [Balamurugan et al. 2004;


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Chao et al. 2008]. The peaks at 2954 and 2877 cm-1 are due to

asymmetric and symmetric stretching vibrations, respectively of CH3

present in methyl group. The strong peak appearing in the region

1732 cm-1 corresponds to the stretching vibrations of carbonyl

functional group (C=O) of methyl present in PMMA chains. The peak

originated at 1437 cm-1 is appearing due to asymmetric bending

vibrations of CH3 present in the chain. Broader and stronger peaks in

the region 1300-1100 cm-1 correspond to ester (C–O) stretching

vibrations. The generation of the peak at 1045 cm-1 is attributed to

–O-CH2 stretching mode. The other peaks present towards lower

wavenumber side correspond to out of plane C–H bending of the PMMA

chains. The presence of all these bands/peaks correspond to the

functional groups present in PMMA and are consistent with the earlier

reports available in the literature [Jo et al. 1989; Balamurugan et al.

2004; Saikia and Kumar 2005; Wang et al. 2006; Khan et al. 2008;

Choudhury and Misra 2010; Tomar et al. 2011].

After embedding PAni.DBSA (1% by weight) in PMMA, the recorded

spectrum ‘b’ indicates that the intensity of almost all the bands/peaks

present in pure PMMA has been reduced considerably indicating the

rearrangement of interactions in PMMA chains on adding PAni.DBSA.

As the concentration of PAni.DBSA is increased to 2% by weight

(spectrum ‘c’), the intensity of the peaks/bands at higher wavenumber

side becomes negligibly small while the decrease in the intensity of

other peaks continues [Shakoor et al. 2009]. With increase in

concentration of PAni.DBSA to 6% by weight in pure PMMA (spectrum

‘d’), only certain peaks corresponding to carbonyl group (1736 cm-1),

CH bonds (2960 cm-1), bending vibration of CH3 (1450 cm-1) and ester

(C-O) vibrations (1300-1100 cm-1) are retained, but with quite small

intensities, and the other peaks are eliminated. Finally, at 10%

concentration by weight of PAni.DBSA (spectrum ‘e’), almost similar

trend as that in spectrum ‘d’ has been noticed except for the more

reduction in the intensity of the remaining peaks.

Thus, the observed behaviour of FTIR spectra of PMMA-PAni.DBSA

blends in comparison to that for pure PMMA clearly indicates that the


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structural rearrangements have taken place after blending PMMA with

PAni.DBSA.

3.2.3 Raman Spectroscopic Studies

As discussed in Chapter 2, Section-2.6 that there are certain bonds

corresponding to symmetric molecules, which are not identified by

FTIR spectroscopic technique. These bonds can show their existence in

Raman spectrum of the molecule. Thus, to explain the structural

rearrangements completely, another complementary technique, i.e.

Raman spectroscopy, was introduced. Figure 3.8 shows the Raman

spectra of PMMA and its blends with varying concentration of

PAni.DBSA.

Figure 3.8 (spectrum ‘a’) clearly indicates the presence of following

peaks in pure PMMA. The peaks at 3004 cm-1 and 2842 cm-1 are

assigned to CH3 asymmetric and CH2 symmetric stretching vibrations,

respectively. These peaks are not clear and partially hidden due to the

sharp and dominating peak at 2956 cm-1, which is corresponding to

CH2 asymmetric stretching vibrations. The peak observed at 1718 cm-1

is attributed due to the C=O stretching mode of ester in carbonyl

group of PMMA. Absorption at 1455 cm-1 is due to the presence of CH2

symmetric bending vibrations. The broad band positioned at 1180 cm-1

is the signature of C-O-C stretching mode. Peaks located at 906 and

988 cm-1 are assigned to C-H in plane bending deformation. This

confirms the chemical structure of PMMA [Ward and Mi 1999;

Tagowska et al. 2004; Silva et al. 2005; Lu et al. 2009; Kumar et al.

2010; Shakoor and Rizvi 2010; Tomar et al. 2012].

On addition of 0.4% by weight of PAni.DBSA to PMMA (spectrum

‘b’), the intensity of the peaks at 3004, 2956, 2842, 1718, 1455, 988

and 814 cm-1 decreases drastically while the band at 1180 cm-1

becomes narrower. In combination of this, several new peaks are

found to emerge at 2443, 2045, 1871, 1645, 1589, 1526, 1392, 1334

and 901 cm-1. The emergence of these new peaks becomes more

prominent at higher concentration of PAni.DBSA in PMMA (curve ‘c’-‘f’).

Most of these peaks (at 1871, 1645, 1526 and 1334 cm-1) are


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corresponding to PAni.DBSA, as already explained in Section-3.1.3, but

with slight change in their positions. The remaining peaks are

originated due to formation of chemical conjugation between functional

groups of PMMA and PAni.DBSA. The broad band at 2310-2556 cm-1

arises due to overtones and combination bands in the chains of both

polymers. The increase in area under this band with the increase in

concentration of PAni.DBSA in PMMA results in the increase in the

conjugation.

Figure 3.8: Raman spectra of PMMA and PMMA-PAni.DBSA blends

The new peak originated at 1392 cm-1 is assigned to the C-N+.

stretching mode of delocalized polaronic charge carrier, which is

responsible for the conduction in the conducting polymers. The

intensity of this peak was found to increase with increase in the

concentration of PAni.DBSA in PMMA. The peak observed at 589 cm-1

in curve ‘b’ is due to the cross-linking between PAni chains [Silva et al.

2005; Shakoor and Rizvi 2009; Tomar et al. 2012]. This peak is red

shifted with increase in its intensity continuously with the increase in

the concentration of PAni.DBSA in blends. Thus, the origination of new


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peaks/bands corresponding to PAni.DBSA confirms its presence in

blends while the other new peaks, which were neither present in

spectrum of PMMA nor in PAni.DBSA, show the formation of new bonds

between the PMMA and PAni.DBSA chains. Further, the increase in the

intensity of peaks corresponding to these new bonds confirms the

increase in conjugation with increase in concentration of PAni.DBSA in

blends.

3.2.4 V-I Measurements

In order to study the conduction properties and charge

transportation mechanism in PMMA-PAni.DBSA blends, Voltage-Current

characteristics have been drawn in the voltage range 0-100 V and are

represented in figure 3.9. For carrying out these studies, the guarded

ring electrode method, as discussed in Chapter 2, Section-2.7.1, was

used.

Figure 3.9: V-I characteristics of PMMA and PMMA-PAni.DBSA blends

From this figure, it is clearly observable that current increases

continuously with increase in the applied voltage for PMMA as well as


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PMMA-PAni.DBSA blends. Further, with the addition of 0.4% by weight

of PAni.DBSA in PMMA, a sudden jump in the current is apparent in the

entire voltage range. As the concentration of PAni.DBSA is increased to

1% by weight, current decreases. This decrease in current may be

attributed to the presence of percolation threshold in this region

[Jachym 1982; Boudenne et al. 2011]. For still higher concentrations,

current again increases rapidly. This rise in the current is observed due

to increase in the conducting PAni.DBSA particles in PMMA, which

makes the hopping of charge carriers easier [Kaiser et al. 2001; Veluru

et al. 2007; Amrithesh et al. 2008].

(a) DC Conductivity

DC conductivity (σdc) of PMMA and its blends with PAni.DBSA at

varying concentration was estimated from V-I characteristics using the

following expression (also discussed in Chapter 2, Section-2.7.1)

Here, t is the thickness of sample and I as the current flowing

corresponding to applied potential V. The average value of conductivity

over the entire voltage range (0-100 V) for PMMA and PMMA-

PAni.DBSA blends are tabulated in table-3.2. It can be clearly seen

from the table that conductivity of PMMA, which was found to be

8.8⨯10-16 S/cm, increases abruptly on adding a very small amount

(0.4% by weight) of PAni.DBSA in it. This may be due to the

generation of charge transfer complexes (CTCs) inside the polymer

matrix, which inject the trapping sites in band gap and hence, are

responsible for the easy migration of charge carriers through the blend

[Jachym 1982; Devi et al. 2002; Baudenne et al. 2011]. Another factor

responsible for increase in conductivity relies on the fact that in PMMA-

PAni.DBSA blends, the conducting PAni.DBSA regions are

interconnected by insulating PMMA regions. By increasing the

concentration of PAni.DBSA, enhancement in conductivity occurs due

to electronic tunnelling through non-conducting PMMA separating


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mesoscopic conducting PAni.DBSA islands [Kaiser et al. 2001;

Amrithesh et al. 2008]. As the concentration of PAni.DBSA is increased

to 1% by weight, conductivity decreases. This may be due to the

presence of percolation threshold in this region [Jachym 1982;

Boudenne et al. 2011]. With further increase in PAni.DBSA content,

charge transfer complexes are increased in the blends decreasing the

barrier heights and in turn, increasing the π electron mobility owing to

increased tunnelling probability and hence, the dc conductivity. At 10%

by weight of concentration of PAni.DBSA in PMMA, a conductivity of

1.15⨯10-9 S/cm has been attained. This means that conductivity of

PMMA has been increased by about 6 orders in magnitude on addition

of 10% PAni.DBSA in PMMA.

(b) Charge Conduction Mechanism

In order to scrutinize the conduction process quantitatively, it is

indispensable to know the actual way of charge migration through

PMMA and its blends with different weight % of PAni.DBSA. The

observed variation of current with applied voltage rules out the

possibility for Ohmic and Space Charge Limited Conduction (SCLC) in

the present case. The other charge transportation mechanisms include

Fowler-Nordheim mechanism, Poole-Frenkel mechanism and Schottky-

Richardson mechanism. The Fowler-Nordheim mechanism is also not

acceptable in the present case because the observed V-I behaviour has

been found to be in contradiction to that required for the applicability

of this conduction mechanism.

To check the applicability of Poole-Frenkel or Schottky-Richardson

mechanisms, the plots between ln(I) and V1/2 have been drawn and

are represented in figure 3.10. From the figure, it is observed that

plots are almost linear with positive slope fulfilling the primary

necessity for applicability of these mechanisms [Dissado and Fothergill

1992; Blythe and Bloor 2005]. To differentiate between the two

mechanisms, the experimental values of βexp for PMMA and PMMA-

PAni.DBSA blends have been determined from the slope of the

respective plots and compared with those corresponding to Poole-


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Frenkel (βPF) and Schottky-Richardson (βSR) mechanisms, calculated as

discussed in Chapter 1, Section-1.4.

Figure 3.10: Plots of ln (I) versus V1/2 for PMMA and PMMA-PAni.DBSA

blends

The experimental values of βexp for PMMA and PMMA-PAni.DBSA

blends at varying concentrations of PAni.DBSA together with the

calculated values of βPF and βSR are listed in table-3.2. It can be seen

from this table that for pure PMMA, the experimental value of β (βexp)

is close to βSR showing the conduction of charge carriers mainly

through Schottky-Richardson mechanism [Deshmukh et al. 2007]. This

result fortifies the insulating character of PMMA with hardly any charge

carriers present in pure PMMA and the observed current is due to the

charge carriers injected from electrodes only on the application of the

field. The effect of application of the field is the reduction in the barrier

at the polymer-metal interface and charges are migrated in the matrix

by crossing the barrier. After adding 0.4% by weight of PAni.DBSA in

PMMA, an increase in the value of βexp is observed but remains closer

to βSR. This shows that at such small concentrations, charge carriers


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induced due to embedding of PAni.DBSA are so less in number that

these are not able to dominate in the charge conduction and the major

role is played by the injected charges only. On increasing the

concentration of PAni.DBSA in PMMA (at 1% by weight), the increase

in of the value of βexp is retained but still rests close to βSR validating

the existence of Schottky-Richardson mechanism as dominating

mechanism for charge transportation in PMMA-PAni.DBSA blends.

Table-3.2: DC conductivity and values of β for PMMA and

PMMA-PAni.DBSA blends

Sample σdc (S/cm) βPF (eV)

(⨯10-5)

(

βSR (eV)

(⨯10-5)

βexp(eV)

(⨯10-5)

Pure PMMA 8.8⨯10-16

3.7

7

1.8

9

1.53

PMMA+0.4% PAni.DBSA 5.37⨯10-14 1.96

PMMA+1% PAni.DBSA 2.16⨯10-15 2.05

PMMA+2% PAni.DBSA 7.87⨯10-11 2.03

PMMA+6% PAni.DBSA 4.60⨯10-10 2.18

PMMA+10% PAni.DBSA 1.15⨯10-9 2.37

The increase in the value of βexp may be attributed to the

generation of charge transfer complexes (CTCs) in PMMA on blending

with PAni.DBSA due to which localized charge states are produced in

the matrix. Due to the presence of these localized states, the

component related to hopping of charge carriers through the matrix

starts playing a role in conduction. At the lower concentrations of

PAni.DBSA in blends, the conducting regions remain far apart resting

the wide barrier in between and hence, hopping of the charges is

difficult. Therefore, majority of the charge carriers responsible for

conduction are injected from the electrodes retaining the Schottky-

Richardson conduction mechanism as the dominating mechanism for

the transportation of charge carriers.

As the concentration of PAni.DBSA is further increased to 2% (by

weight) and above in blends, the increase in the value of βexp


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continues. This may be due to the reason that with increasing

concentrations, the conducting islands of PAni.DBSA come closer

favouring the charges to hop from one conducting region to another

increasing the interwell hopping and hence, the conduction. For 10%

by weight of PMMA-PAni.DBSA blends, βexp lies in between βSR and βPF,

but still nearer to βSR than βPF; thus, migration of charges can be

assumed to be through both the mechanisms simultaneously yet the

Schottky-Richardson mechanism dominates over the Poole-Frenkel

mechanism.

From the above discussion, it can be concluded that the migration

of the charge carriers, which is through Schottky-Richardson

conduction mechanism for pure PMMA and its blends with lower

concentration of PAni.DBSA also includes the conduction through

Poole-Frenkel mechanism as the concentration of PAni.DBSA is

increased in PMMA-PAni.DBSA blends.

3.2.5 Dielectric Measurements

To understand the dielectric behaviour of PMMA and its blends with

varying concentration of PAni.DBSA, the various dielectric parameters,

like dielectric constant, dielectric loss and ac conductivity have been

studied as a function of frequency of the applied electric field. In the

present section, these parameters are discussed one by one.

(a) Dielectric Constant and Dielectric Loss

Figures 3.11 and 3.12 show the frequency (75 kHz–5 MHz)

dependent variation in dielectric permittivity ℇ’ and dielectric loss ℇ’’,

respectively at room temperature for PMMA and PMMA-PAni.DBSA

blends at different concentration of PAni.DBSA. As shown in figure

3.11, a decrease in the value of ℇ’ with the increase in frequency has

been observed for pure PMMA and PMMA-PAni.DBSA blends. The

pronounced nature of dielectric permittivity in low frequency region is

attributed to the interfacial polarization (arises only when the phases

with different conductivities are present) and due to the electrode

effect (originates as a result of blockage of the charge at the


91

electrode). This may also be credited to the tendency of induced

dipoles in polymeric samples to orient themselves in the direction of

applied field, when the frequency alteration is low [Mardare 2004]. The

observed decrease in ℇ’ with increase in frequency may be due to the

contribution of orientation relaxation of dipoles and conduction of

charge carriers at higher frequency [Dyre 1988]. This can be explained

on the basis of the fact that at high frequency, field reversal becomes

so fast that dipoles are unable to orient themselves with the field and

intrawell hopping probability of charge carriers dominates.

Figure 3.11: Variation of dielectric constant with frequency for PMMA

and PMMA-PAni.DBSA blends

As also depicted from figure 3.11 that with the increase in

concentration of PAni.DBSA (curves ‘b–f’), the value of ℇ’ decreases in

complete frequency range. It is well known that the doped PAni system

contains two types of charged species, i.e. polaron/bipolaron system

and bound charges (dipoles). The polaron/bipolaron system is mobile

and free to move along the chain, while dipoles have only restricted


92

mobility and account for strong polarization in the system. Thus, the

presence of conducting islands of PAni.DBSA (charged species) in

insulating PMMA matrix is responsible for the enhanced conduction of

charge carriers (polaron/bipolaron and bound charges of PAni.DBSA)

through hopping in PMMA chains [Joo et al. 1998; Pinto et al. 2000;

Gmati et al. 2008; Afjal 2010].

When the filler (PAni.DBSA) content is low, mean distance between

the PAni.DBSA clusters is sufficiently large and conduction is restricted

by the presence of the dielectric matrix. However, by increasing the

conductive phase content, metallic islands get closer and a physical

path is formed through which the current can flow percolating the

whole system [Veluru et al. 2007], thus, supporting the observed

decrease in ℇ’ as the concentration of PAni.DBSA in PMMA increases.

The values of dielectric constant at various frequencies are tabulated in

table-3.3. It can be concluded from the table that at the frequency of

1 MHz, the value of dielectric constant decreases from 4.03 (pure

PMMA) to 1.88 after the dispersion of 10 % by weight of PAni.DBSA in

PMMA.

Table-3.3: Values of dielectric constant for PMMA and PMMA-

PAni.DBSA blends

Sample

Dielectric Constant at

100 kHz 500 kHz 1 MHz

Pure PMMA 4.28 4.08 4.03

PMMA+0.4% PAni.DBSA 3.92 3.68 3.60

PMMA+1% PAni.DBSA 3.50 3.27 3.18

PMMA+2% PAni.DBSA 3.54 3.27 3.17

PMMA+6% PAni.DBSA 2.79 2.33 2.13

PMMA+10% PAni.DBSA 2.35 2.00 1.88


93

The variation in imaginary part of dielectric constant ℇ’’ (dielectric

loss) with frequency for pure PMMA and different PMMA-PAni.DBSA

blends is shown in figure 3.12. It is obvious from this figure that ℇ’’

decreases with increase in frequency. At low frequency, the high value

of dielectric loss ℇ’’ is usually associated with the motion of free charge

carriers within the material: dipole polarization or interfacial

polarization. At high frequency, periodic field reversal is so fast that

there is no excess ion diffusion in the direction of electric field and

thus, charge accumulates and forms the space charge [Dyre 1988;

Mardare 2004]. Polarization decreases due to accumulation of charges

leading to the decrease in ℇ’’. Further, the higher value of the dielectric

loss for the higher concentration of dopant (curve ‘b–f’) can be

understood in terms of electrical conductivity, which is associated with

the dielectric loss.

Figure 3.12: Variation of dielectric loss with frequency for PMMA and

PMMA-PAni.DBSA blends


94

(b) AC Conductivity

Figure 3.13 represents the variation in ac conductivity (σac) for

pure PMMA and PMMA-PAni.DBSA blends. It is observable from this

figure that the value of σac increases up to 2 weight % of PAni.DBSA at

different frequencies. This is in accordance with the Random free

energy barrier (RFEB) model [Dyre 1988]. According to this model,

conductance is an increasing function of frequency in many disordered

solids, including polymers, which can be explained on the basis of any

hopping model. Thus, charge transport is through hopping from the

conductive islands of PAni.DBSA particles, which are distributed among

the insulating region of PMMA giving rise to increase in conductivity

with the increase in filler concentration.

Figure 3.13: Variation of ac conductivity with concentration of

PAni.DBSA in PMMA at different frequencies

Due to the fast reversal of applied time varying electric field,

dipoles remain polarized and the charge carriers are able to hop from

one dipolar conducting region to another, which is responsible for the

good conductivity of the PMMA-PAni.DBSA blends. As the percolation

threshold is obtained, the system changes its behaviour and ac


95

conductivity becomes nearly uniform above percolation threshold, as

depicted from figure 3.13.

From the above discussion, it can be conferred that the

embedding of PAni.DBSA in PMMA results in the significant

changes in the optical, electrical and structural properties of

PMMA. Such a variation is found to be consistent with the

increase in concentration of PAni.DBSA in PMMA-PAni.DBSA

blends.

3.3 PMMA-PANI.CSA BLENDS

In the present section, results of the similar studies, as discussed

in Section-3.2 for PMMA-PAni.DBSA blends, have been presented for

PMMA on blending with PAni doped with another acid, i.e. CSA. For

this, same characterization tools and methods have been adopted as

those for PMMA-PAni.DBSA blends.

3.3.1 UV-Visible-NIR Absorption Studies

Figure 3.14 presents the UV-visible-NIR absorption spectra of

PMMA and its blends with different concentration (0.4, 1.0, 2.0, 6.0

and 10.0; % by weight) of PAni.CSA. Curve ‘a’ of this figure clearly

indicates the existence of two absorption peaks in UV-region, i.e. at

298 nm and 340 nm in PMMA, while it remains almost transparent in

complete visible region [Jin et al. 1992], as already discussed in

Section-3.2.1. On blending PMMA with PAni.CSA, two additional new

bands at around 449 nm and 829 nm become apparent at higher

concentrations (6% and 10% by weight) of PAni.CSA in PMMA. These

new bands correspond to π → π* transitions and polaron band

transitions, respectively of PAni.CSA [Ong et al. 1997; Mamunya et al.

2002; Laska 2004; Ebrahim et al. 2009; Wallace et al. 2009]. This

confirms the presence of PAni.CSA in PMMA-PAni.CSA blends.

Furthermore, a continuous shift towards the higher wavelengths in

the absorption edge corresponding to PMMA has been observed on

increasing the concentration of PAni.CSA in PMMA and may be


96

explained on the similar basis as that for PMMA-PAni.DBSA blends

discussed in Section-3.2.1.

Figure 3.14: UV-Visible-NIR absorption spectra of PMMA and PMMA-

PAni.CSA blends

Determination of Optical Energy Gap

In order to determine the change in optical energy gap of PMMA on

addition of different weight % of PAni.CSA, the values of (αhυ)1/2 as a

function of photon energy (hυ), corresponding to the fundamental

absorption edge of the respective UV-Visible-NIR spectra, have been

plotted in light of the Tauc’s relation [Tauc 1974; Fink 2004; Mighad

and Zidan 2006; Kumar et al. 2011]. The linear fitted lines of these

plots have been extrapolated to hυ axis (figure 3.15) and the

intercepts on this axis provided the respective values of optical energy

gap. These values for pure PMMA and its blends with varying

concentration of PAni.CSA are listed in table-3.4.


97

Figure 3.15: Plots to determine optical energy gap for PMMA and

PMMA-PAni.CSA blends

Table 3.4: Optical energy gap values for PMMA and PMMA-

PAni.CSA blends

Sample Optical Energy Gap (eV)

Pure PMMA 2.72 ± 0.02

PMMA+0.4% PAni.CSA 2.49 ± 0.01

PMMA+1% PAni.CSA 2.26 ± 0.01

PMMA+2% PAni.CSA 2.04 ± 0.02

PMMA+6% PAni.CSA 1.98 ± 0.01

PMMA+10% PAni.CSA 1.90 ± 0.03


98

From the figure 3.15 and table-3.4, it is clear that the value of

optical energy gap, which comes out to be 2.72 eV for pure PMMA, has

been reduced continuously with increasing concentration of PAni.CSA

in PMMA and attains a value of 1.90 eV for 10% concentration by

weight of PAni.CSA. Such a reduction in the optical energy gap values

may be correlated to the induced structural rearrangements causing

generation of trap levels between HOMO and LUMO of PMMA on

blending it with different amount of PAni.CSA [Devi et al., 2002;

Mamunya et al. 2002; Laska 2004; Ebrahim et al. 2009], as already

explained in detail for PMMA-PAni.DBSA blends in Section-3.2.1.

3.3.2 FTIR Spectroscopic Studies

FTIR spectroscopy has been utilized to gather the information

regarding the chemical rearrangements in PMMA on blending with

PAni.CSA at different concentrations. Figure 3.16 presents the FTIR

spectra for PMMA and different PMMA-PAni.CSA blends. Spectrum ‘a’ of

this figure shows the absorption corresponding to functional groups

present in pure PMMA, as already discussed in Section-3.2.2 [Jo et al.

1989; Balamurugan et al. 2004; Saikia and Kumar 2005; Wang et al.

2006; Chao et al. 2008; Khan et al. 2008; Shakoor et al. 2009;

Choudhury and Misra 2010; Tomar et al. 2011].

With the addition of PAni.CSA in PMMA, a continuous reduction in

the intensity of almost all the peaks with increasing concentration of

PAni.CSA in PMMA has been observed (spectra ‘b’ to ‘f’). Further,

almost complete elimination of the bands at wavenumbers above

2500 cm-1 has been observed for 6% and 10% by weight

concentration of PAni.CSA in PMMA. Such changes in the FTIR spectra

could be due to the screening produced by PAni.CSA particles within

the chains of PMMA and the formation of chemical bonding between

the functional groups of PMMA and PAni.CSA, resulting in the structural

rearrangements in PMMA chains.


99

Figure 3.16: FTIR spectra of PMMA and PMMA-PAni.CSA blends

3.3.3 Raman Spectroscopic Studies

In order to analyse the induced structural changes in PMMA on

blending with PAni.CSA in more detail, another spectroscopic

technique, i.e. Raman spectroscopy, has been utilized. Figure 3.17

shows the Raman spectra of PMMA and its blends with varying

concentration of PAni.CSA. Spectrum ‘a’ of this figure depicts the

various bonds present in PMMA, as already discussed in detail in

Section-3.2.3 [Ward and Mi 1999; Tagowska et al. 2004; Silva et al.

2005; Lu et al. 2009; Kumar et al. 2010; Shakoor and Rizvi 2010;

Tomar et al. 2012].

It is apparent from the figure that the intensity of various

characteristic peaks in PMMA, i.e. at 3004, 2956, 2842, 1718, 1455,

988 and 814 cm-1, has been found to be reduced continuously with

increasing concentration of PAni.CSA in PMMA while the band at

1180 cm-1 becomes narrower. The peaks observed at 1592 and

1521 cm-1 are corresponding to PAni.CSA in PMMA. In addition, new


100

peaks/bands at 2443, 1983, 1558 and 1045 cm-1 are observed to

emerge out due to formation of chemical conjugation of PAni.CSA with

PMMA. These new peaks are observable more clearly at higher

concentrations of PAni.CSA in PMMA (curve ‘c’-‘f’). In combination of

these changes, the presence of broad band at 2310-2556 cm-1 arises

due to overtones and combination bands in the chains of both

polymers. Further, increase in the area under this band with increasing

concentration of PAni.CSA in PMMA corroborates towards the increased

conjugation in the blends.

Figure 3.17: Raman spectra of PMMA and PMMA-PAni.CSA blends

The new peak originated at 1382 cm-1, as an effect of addition of

PAni.CSA in PMMA, may be assigned to the C-N+. stretching mode of

delocalized polaronic charge carriers. The increased intensity of this

peak is an indication towards the increased conductivity of blends with

increase in PAni.CSA content. Thus, the change in the spectrum of

pure PMMA and origination of new peaks/bands in PMMA-PAni.CSA

blends show the formation of new bonds between the PMMA and

PAni.CSA chains. Further, the increase in the intensity of peaks


101

corresponding to these new bonds corroborates towards the increased

conjugation in PMMA-PAni.CSA blends with increase in concentration of

PAni.CSA in PMMA.

3.3.4 V-I Measurements

To determine the dc conductivity and charge conduction

mechanism in PMMA and PMMA-PAni.CSA blends, Voltage-Current

measurements were carried out in the voltage range 0-100 V and are

represented in figure 3.18. Similar trends in V-I characteristics as that

for PMMA-PAni.DBSA blends (Section-3.2.4) have been observed.

Figure 3.18: V-I characteristics of PMMA and PMMA-PAni.CSA blends

(a) DC Conductivity

DC conductivity (σdc) of PMMA-PAni.CSA blends at varying

concentration of PAni.CSA in PMMA have been determined following

the same procedure as that for PMMA-PAni.DBSA blends, discussed in

Section-3.2.4. The average values of conductivity in entire voltage

range (0-100 V) for PMMA and PMMA-PAni.CSA blends are appended in


102

table-3.5. This table clearly indicates an increase in conductivity with

increasing concentration of PAni.CSA in PMMA.

The value of dc conductivity, which comes out to be

8.8⨯10-16 S/cm for pure PMMA changes to 1.97⨯10-10 S/cm, i.e. by

about 5 orders of magnitude, after embedding 10% by weight

concentration of PAni.CSA in PMMA. This may be attributed to the

formation of charge transfer complexes (CTCs) inside the polymer

matrix leading to the generation of traps in band gap [Kaiser et al.

2001; Amrithesh et al. 2008]. Due to this, interwell barrier strength

decreases and in turn, π-electron mobility through the chains increases

owing to increased tunnelling probability and finally, the dc

conductivity, as already discussed in Section-3.2.4 for PMMA-

PAni.DBSA blends.

(b) Charge Conduction Mechanism

Like that for PMMA-PAni.DBSA blends (figure 3.10), the linear

behaviour with positive slope of the plots between ln(I) and V1/2, as

presented in figure 3.19 for PMMA and PMMA-PAni.CSA blends,

endorse the applicability of Poole-Frenkel or Schottky-Richardson

mechanisms. From the slope of these plots, the values of βexp for PMMA

and PMMA-PAni.CSA blends have been determined and presented in

table-3.5 alongwith the values of β corresponding to Poole-Frenkel

(βPF) and Schottky-Richardson (βSR) mechanisms. The comparison of

the results presented in table-3.5 for PMMA-PAni.CSA blends with

those corresponding to PMMA-PAni.DBSA blends (table-3.2) clearly

indicates the similar conduction behaviour in both PMMA-PAni.DBSA

and PMMA-PAni.CSA blends. Therefore, the migration of the charge

carriers for pure PMMA and PMMA-PAni.CSA blends at lower

concentrations (upto 1% by weight) indicates the conduction through

Schottky-Richardson conduction mechanism while at higher

concentrations; the conduction mechanism may include the

contribution of Poole-Frenkel mechanism also.


103

Figure 3.19: Plots of ln (I) versus V1/2 for PMMA and PMMA-PAni.CSA

blends.

Table-3.5: DC conductivity and values of β for PMMA and


Sample σdc (S/cm) βPF (eV)

(⨯10-5)

βSR (eV)

(⨯10-5)

βexp(eV)

(⨯10-5)

Pure PMMA 8.80⨯10-16

3.7

7

1.8

9

1.53

PMMA+0.4% PAni.CSA 7.77⨯10-13 1.84

PMMA+1% PAni.CSA 2.21⨯10-12 1.92

PMMA+2% PAni.CSA 7.61⨯10-11 2.05

PMMA+6% PAni.CSA 1.78⨯10-10 2.21

PMMA+10% PAni.CSA 1.97⨯10-10 2.42


104

3.3.5 Dielectric Measurements

In order to understand the dielectric behaviour of PMMA and

PMMA-PAni.CSA blends, dielectric measurements in the frequency

range 20 Hz to 1 MHz were carried out at room temperature. From the

recorded data, dielectric constant, dielectric loss and ac conductivity

have been determined as a function of frequency.

(a) Dielectric Constant and Dielectric Loss

Figure 3.20 presents the variation in dielectric constant (ℇ’) as a

function of frequency for PMMA and PMMA-PAni.CSA blends with

different concentration of PAni.CSA. It is evident from the figure that

at lower frequencies, the values of dielectric constant are quite higher

and reduce continuously with increase in frequencies. Further, a clear

cut decrease in dielectric constant with increase in the concentration of

PAni.CSA has been noticed at the same frequency. The values of

dielectric constant at different frequencies for PMMA-PAni.CSA blends

are also presented in table-3.6.

Figure 3.20: Variation of dielectric constant with frequency for PMMA

and PMMA-PAni.CSA blends


105

Table-3.6: Values of dielectric constant for PMMA and PMMA-

PAni.CSA blends

Sample

Dielectric Constant at

100 kHz 500 kHz 1 MHz

Pure PMMA 4.57 4.19 4.06

PMMA+0.4% PAni.CSA 4.39 3.94 3.78

PMMA+1% PAni.CSA 4.13 3.53 3.31

PMMA+2% PAni.CSA 3.93 3.32 3.10

PMMA+6% PAni.CSA 2.81 2.34 2.17

PMMA+10% PAni.CSA 2.50 2.08 1.93

Figure 3.21 depicts the variation in dielectric loss (ℇ’’) with

frequency for pure PMMA and PMMA-PAni.CSA blends at varying

concentration of PAni.CSA. It is obvious from this figure that ℇ’’

decreases with increase in frequency.

Figure 3.21: Variation of dielectric loss with frequency for PMMA and



106

However, the values of dielectric loss at the same frequency

increase continuously with increase in concentration of PAni.CSA. The

observed behaviour of ℇ’ and ℇ’’ for PMMA-PAni.CSA blends is

consistent with that observed for PMMA-PAni.DBSA blends, as

presented in Section-3.2.5.

(b) AC Conductivity

Figure 3.22 represents the variation in ac conductivity (σac) plotted

as a function of the concentration of PAni.CSA in PMMA at different

frequencies. It is clearly observable from the figure that the value of ac

conductivity increases with increase in the concentration of PAni.CSA

for all frequencies. Moreover, increase in the conductivity is more

pronounced upto a concentration of 2% by weight of PAni.CSA in

PMMA; and at the higher concentrations, the increase is somewhat

slow and conductivity is almost uniform indicating the change in the

behaviour at the percolation threshold.

Figure 3.22: Variation of ac conductivity with concentration of

PAni.CSA in PMMA at different frequencies


107

When the frequency of 1 MHz is attained, fast increase in the

conductivity has been observed. This may be due to the reason that in

the fast reversal of applied time varying electric field, dipoles remain

polarized and the charge carriers are able to hop from one dipolar

conducting region to another, which is responsible for the good

conductivity of the PMMA-PAni.CSA blends at higher frequencies.

From the above discussion, it is apparent that the similar trends

related to dielectric constant, dielectric loss and ac conductivity for

PMMA-PAni.CSA blends have been observed as those for PMMA-

PAni.DBSA blends. Therefore, the variation in the values of these

parameters for PMMA-PAni.CSA blends can be understood in the

similar manner as that explained in detail for PMMA-PAni.DBSA blends

(Section-3.2.5).

3.4 A RELATIVE COMPARISON

As already discussed in Section-3.2 and 3.3, in the present work, a

systematic study related to the variation in the optical, electrical and

structural properties of PMMA on blending with different concentration

of PAni.DBSA and PAni.CSA, respectively has been carried out. In this

section, a comparison of the induced changes in the properties of

PMMA, as an effect of embedding of PAni.DBSA and PAni.CSA, has

been made.

Figure 3.23 presents the variation in optical energy gap of PMMA

with increasing filler concentration of PAni.DBSA (curve ‘a’) and

PAni.CSA (curve ‘b’). It is clearly observable from the figure that there

exists a clear cut decrease in optical energy gap of PMMA with

increasing filler concentration. However, the effect is more pronounced

with about 34% reduction in optical energy gap after embedding

PAni.DBSA as compared to about 30% for PAni.CSA, at the maximum

filler concentration of 10% by weight in both cases. As far as the dc

electrical conductivity is concerned, as shown in figure 3.24, the same

is found to be increased significantly with increasing filler concentration

in PMMA by about 6 orders of magnitude for PAni.DBSA and by about


108

5 orders of magnitude for PAni.CSA at same concentration of 10% by

weight.

Figure 3.23: Variation of optical energy gap versus concentration of

PAni.DBSA/PAni.CSA in PMMA

Figure 3.24: Variation in dc conductivity versus concentration of

PAni.DBSA/PAni.CSA in PMMA


109

The more pronounced effects in optical and conductivity

behaviour of PMMA-PAni.DBSA as compared to PMMA-PAni.CSA

blends are well explained on the basis of induced structural

rearrangements, being more prominent in case of PAni.DBSA,

as revealed through FTIR and Raman spectroscopy. The above

results seem to consider PMMA-PAni.DBSA as the better

material for fabrication of electronic and opto-electronic

devices than PMMA-PAni.CSA.

Regarding dielectric behaviour of PMMA-PAni.DBSA and PMMA-

PAni.CSA composites at different filler concentrations, as shown in

table-3.7, no significant change in the values of dielectric constant, on

embedding PAni.DBSA and PAni.CSA at same concentration, has been

observed. However, the increase in dielectric loss is more pronounced

in PAni.DBSA as compared to PAni.CSA. This trend indicates PMMA-

PAni.CSA to be a better dielectric material in comparison to PMMA-

PAni.DBSA.

Table-3.7: Comparison of frequency dependant electrical

parameters for blends of PAni.DBSA/PAni.CSA with

PMMA (at 1 MHz frequency)

PAni content in

PMMA

(% by weight)

Dielectric Constant Dielectric Loss

PAni. DBSA PAni. CSA PAni. DBSA PAni. CSA

0 4.03 4.06 1.21 1.21

0.4 3.60 3.78 2.40 1.23

1 3.18 3.31 3.43 1.35

2 3.17 3.10 4.61 1.63

6 2.13 2.17 5.51 1.97

10 1.88 1.93 6.61 2.16


110

From the above, it is apparent that considerable reduction

in optical energy gap, significantly large increase in

conductivity, decrease in dielectric constant and increase in

dielectric loss have been observed on blending PMMA with

PAni.DBSA/PAni.CSA with increasing concentrations.

CONCLUSION

Blending of PAni (acid doped) with PMMA produces a continuous

change in optical, electrical and structural properties of this polymer

with increasing filler concentration. About 34% reduction in optical

energy gap, by about 6 orders of magnitude enhancement in dc

conductivity and considerably large variation in dielectric parameters

have been perceived at 10% concentration by weight of the embedded

PAni.DBSA in PMMA. Similar trends, although slightly less pronounced,

in PMMA-PAni.CSA blends have been observed.


111

REFERENCES Afzal A.B., Akhtar M.J., Nadeem M., Ahmad M., Hassan M.M., Yasin T.,

Mehmood M., “Structural and electrical properties of

polyaniline/silver nanocomposites”, J. Phys. D: Appl. Phys. 42

(2009) 015411.

Afzal A.B., Akhtar M.J., Nadeem M., Hassan M.M., “Dielectric and

impedance studies of DBSA doped polyaniline/PVC composites”,

Current Applied Physics 10 (2010) 601.

Ameen S., Ali V., Zulfequar M., Haq M.M., Husain M., “Electrical and

spectroscopic characterization of polyaniline–polyvinyl chloride

(PANI–PVC) blends doped with sodium thiosulphate”, Physica B:

Condens. Matter 403 (2008) 2861.

Amrithesh M., Aravind S., Jayalekshmi S., Jayasree R.S., “Enhanced

luminescence in Polyaniline-Poly(methyl methacrylate)

composites”, J. Alloys Comp. 449 (2008) 176.

Araujo P.L.B., Araujo E.S., Santos R.F.S. and Pacheco A.P.L., “Synthesis and

morphological characterization of PMMA/Polyaniline nanofiber

composites”, Microelect. J. 36 (2005) 1055.

Balamurugan A., Kannan S., Selvaraj V., and Rajeswari S., “Development

and Spectral Characterization of Poly(Methyl Methacrylate)

/Hydroxyapatite Composite for Biomedical Applications”, Trends

Biomater. Artif. Organs 18 (2004) 41.

Bellamy L.J., “The Infra-red Spectra of Complex Molecules”, Richard

Clay, Bungay, Suffolk (1962).

Bhat N.V., Sheshadri D.T., Phadke R.S., “Simultaneous polymerization

and crystallization of aniline”, Synth. Met. 130 (2002) 285.

Blythe A.R., “Electrical Properties of Polymers”, Cambridge University

Press, Cambridge (1979).

Blythe A.R., “Electrical Resistivity Measurements of Polymer Materials”,

Polymer Testing 4 (1984) 195.

Blythe T. and Bloor D., “Electrical Properties of Polymers”, Cambridge

University Press, New York, USA (2005).

Boudenne A., Ibos L., Candau Y., Thomas S., “Handbook of Multiphase

Polymer Systems: Vol. 1”, John Wiley & Sons Ltd., West Sussex,

United Kingdom (2011).

Boyer M.I., Quillard S., Rebourt E., Louarn G., Buisson J.P., Monkman A.,

Lefrant S., “Vibrational Analysis of Polyaniline: A Model

Compound Approach”, J. Phys. Chem. B 102 (1998) 7382.


112

Boyer M.L., Quillard S., Louarn G., Froyer G., Lefrant S., “Vibrational Study

of the FeCl3-Doped Dimer of Polyaniline; A Good Model

Compound of Emeraldine Salt”, J. Phys. Chem. B 104 (2000) 8952.

Cao Y., Smith P., Heeger A.J., “Spectroscopic studies of Polyanilinein

solution and in spin cast films”, Synth. Met. 32 (1989) 263.

Chao L., Huang Y.J., Han Y.K., Tseng P.H., Hsieh T.H., Lin C.M. and Ho K.S.,

“Shearing Effects on the Conducting Polymer Blends”, Polym.

Bull. 60 (2008) 847.

Choudhury T. and Misra N.M., “Thermal stability of PMMA–clay hybrids”,

Bull. Mater. Sci. 33 (2010) 165.

Colomban P.A., Cruger A., Novak A., Regis A., “Infrared and Raman study

of polyaniline Part I. Hydrogen bonding and electronic mobility

in emeraldine salts”, J. Mol. Struct. 317 (1994) 261.

Deshmukh S.H., Burghate D.K., Akhare V.P., Deogaonkar V.S., Deshmukh

P.T. and Deshmukh M.S., “Electrical Conductivity of Polyaniline

Doped PVC–PMMA Polymer Blends”, Bull. Mater. Sci. 30 (2007) 51.

Devi C.U., Sharma A.K. and Rao V.V.R.N., “Electrical and Optical

Properties of Pure and Silver Nitrate-Doped Polyvinyl Alcohol

Films”, Mater. Lett. 56 (2002) 167.

Dhawan S.K., Singh N., Rodrigues D., “Electromagnetic shielding

behaviour of conducting Polyaniline composites”, Sci. Tech. Adv.

Mater. 4 (2003) 105.

Dissado L.A. and Fothergill J.C., “Electrical degradation and breakdown in

polymers”, Peter Peregrinus Ltd, UK (1992).

Dyre J.C., “The random free‐energy barrier model for ac conduction in

disordered solids”, J. Appl. Phys. 64 (1988) 2456.

Ebrahim S., Kashyout A.H., Soliman M., “Ac and Dc conductivities of

polyaniline/poly vinyl formal blend films”, Current Applied Physics

9 (2009) 448.

Epstein A.J., “Electrically conducting polymers: Science and

Technology”, MRS Bulletin (June 1997) 16.

Epstein A.J., Ginder J.M., Zuo F., Bigelow R.W., Woo H.S., Tanner D.B.,

Richter A.F., Huang W.S., MacDiarmid A.G., “Insulator-to-metal

transition in Polyaniline”, Synth. Met. 18 (1987) 303.

Fink D. (Ed.), “Fundamentals of Ion-Irradiated Polymers”, Springer-

Verlag, Berlin, Heidelberg (2004).


113

Gmati F., Fattoum A., Bohli N., Mohamed A.B., “Effects of the molar mass

of the matrix on electrical properties, structure and morphology

of plasticized PANI–PMMA blends”, J. Phys.: condens. Matter 20

(2008) 125221.

Hasik M., Paluszkiewicz C., Wenda E., “Interactions between polyanilines

and platinum(IV) ions: vibrational spectroscopic studies”, Vib.

Spectrosc. 29 (2002) 191.

Ikkala O.T., Pietila l.O., Ahjopado L., Osterholm H., Passiniemi J., “On the

molecular recognition and associations between electrically

conducting polyaniline and solvents”, J. Chem. Phys. 103 (1995)

9855.

Jachym B. (Ed. E.K. Sichel), “Carbon Black Polymer Composites”, Marcel

Dekker Inc., New York (1982).

Jain S.C., Willander M., Kumar V., “Conducting Organic Materials and

Devices: Semiconductors and Semimetals, Volume 81”,

Academic Press, London, UK (2007).

Jin S., Tiefel T.H., Wolfe R., Sherwood Jr. R.C., Mottine J.J., “Optically

Transparent, Electrically Conductive Composite Medium”,

Science 255 (1992) 446.

Jo W.H., Cruz C.A., Paul D.R., “FTIR investigation of interactions in

blends of PMMA with a styrene/acrylic acid copolymer and their

analogs”, Journal of Polymer Science Part B: Polymer Physics 27

(1989) 1057.

Joo J., Long S.M., Pouget J.P., Oh E.J., MacDiarmid A.G., Epstein A.J.,

“Charge transport of the mesoscopic metallic state in partially

crystalline polyanilines”, Phys. Rev. B 57 (1998) 9567.

Kaiser A.B., “Electronic transport properties of conducting polymers

and carbon nanotubes”, Rep. Prog. Phys. 64 (2001) 1.

Kang E.T., Neoh K.G. and Tan K.L., “Polyaniline: A polymer with many

interesting intrinsic redox states”, Prog. Polym. Sci. 23 (1998)

277.

Khan M.S., Qazi R.A. and Wahid M.S., “Miscibility studies of PVC/PMMA

and PS/PMMA blends by dilute solution viscometry and FTIR”,

African Journal of Pure and Applied Chemistry 2 (2008) 041.

Kim Y.H., Foster C., Chiang J., Heeger A.J., “Photoinduced localized

charged excitations in Polyaniline”, Synth. Met. 26 (1988) 49.


114

Kohlman R.S., Zibold A., Tanner D.B., Ihas G.G., Ishiguro T., Min Y.G.,

MacDiarmid A.G., Epstein A.J., “Limits for metallic conductivity in

conducting polymers”, Phys. Rev. Lett. 78 (1997) 3915.

Kumar S., Sharma A., Tripathi B., Srivastava S., Agrawal S., Singh M.,

Awasthi K., Vijay Y.K., “Enhancement of hydrogen gas

permeability in electrically aligned MWCNT-PMMA composite

membranes”, Micron 41 (2010) 909.

Kumar V., Goyal P.K., Mahendia S., Gupta R., Sharma T. and Kumar S.,

“Tuning of Refractive Index and Optical Band Gap of CR-39

Polymer by Heating”, Rad. Eff. Def. Solids 166 (2011) 109.

Laska J., “Conformations of polyaniline in polymer blends”, J. Mole.

Struc. 701 (2004) 13.

Lu Z., Wang J., Li Q., Chen L., Chen S., “Controllable synthesis of

nanosilica surface-grafted PMMA macromonomers via catalytic

chain transfer polymerization”, Eur. Poly. J. 45 (2009) 1072.

Malmonge L.F., Lopes G.D.A., Langiano S.D.C., Malmonge J.A., Cordeiro

J.M.M., Mattoso L.H.C., “A new route to obtain PVDF/PAni

conducting blends” Eur. Poly. J. 42 (2006) 3108.

Mamunya Y., Muzychenko W., Pissis P., Lebedev E., Shut M., “Percolation

phenomena in polymers containing dispersed iron”, Polym. Eng.

Sci. 42 (2002) 90.

Mardare D. and Rusu G.I., “Comparison of the Dielectric Properties For

Doped and Undoped TiO2 Thin Films”, J. Optoelectron. & Adv.

Mater. 6 (2004) 333.

Masters J.G., Sun Y., Macdiarmid A.G., Epstein A.J., “Polyaniline: allowed

oxidation states”, Synth. Met. 41 (1991) 715.

Migahed M.D. and Zidan H.M., “Influence of UV-Irradiation On The

Structure and Optical Properties of Polycarbonate Films”, Curr.

App. Phys. 6 (2006) 91.

Neoh K.G., Kang E.T., Tan K.L., “Evolution of polyaniline structure during

synthesis”, Polymer 34 (1993) 3921.

Ong C.H., Goh S.H. and Chan H.S.O., “Conductive Polyaniline/Poly(vinyl

phosphonic acid) blends”, Polym. Bull. 39 (1997) 627.

Ping Z., “In situ FTIR–attenuated total reflection spectroscopic

investigations on the base–acid transitions of polyaniline.

Base–acid transition in the emeraldine form of Polyaniline”, J.

Chem. Soc., Faraday Trans. 92 (1996) 3063.


115

Pinto N.J., A.A. Acosta, G.P. Sinha, F.M. Aliev, “Dielectric permittivity

study on weakly doped conducting polymers based on

polyaniline and its derivatives”, Synth. Met. 113 (2000) 77.

Saikia D. and Kumar A., “Ionic transport in P(VDF-HFP)–PMMA–

LiCF3SO3–(PC+DEC)–SiO2 composite gel polymer electrolyte”,

Eur Polym J. 41 (2005) 563.

Shakoor A. and Rizvi T.Z., “Raman spectroscopy of conducting

poly(methylmethacrylate)/Polyaniline-dodecylbenzene sulfonic

acid blends”, J. Raman Spectrosc., 41 (2010) 237.

Shakoor A., Rizvi T.Z., and Anwar H., “Morphological, Thermal, and

Conductivity Studies of Poly(methyl methacrylate)/Polyaniline

Dodecylbenzenesulfonate Blends”, Polymer Science 51 (2009) 898.

Silva J.E.P.d., Temperini M.L.A. and Torresi S.I.C.d., “Characterization of

Conducting Polyaniline Blends by Resonance Raman

Spectroscopy”, J. Braz. Chem. Soc. 16 (2005) 322.

Socrates G., “Infrared and Raman Characteristic Group Frequencies”,

John Wiley, New York (2001).

Sze S.M., “Physics of Semiconductor Devices”, John Wiley and Sons

(ASIA) Pvt. Ltd., Singapur (2004).

Tagowska M., Pałys B., Jackowska K., “Polyaniline nanotubules—anion

effect on conformation and oxidation state of polyaniline

studied by Raman spectroscopy”, Synth. Met. 142 (2004) 223.

Tauc, “Amorphous and Liquid Semiconductors”, Plenum Press, (1974).

Tomar A.K., Mahendia S. and Kumar S., “Structural characterization of

PMMA blended with chemically synthesized PAni”, Advances in

Applied Science Research 2 (2011) 327.

Tomar A.K., Mahendia S., Chahal R.P., Kumar S., “Structural and dielectric

spectroscopic studies of polyaniline–poly(methyl methacrylate)

composite films”, Synth. Met. 162 (2012) 820.

Trchová M. and Stejskal J., “Polyaniline: The infrared spectroscopy of

conducting polymer nanotubes (IUPAC Technical Report)”, Pure

Appl. Chem. 83 (2011) 1803.

Veluru J.B., Satheesh K.K., Trivedi D.C., Ramakrishna M.V., Srinivasan N.T.,

“Electrical properties of electrospun fibers of PANI-PMMA

composites”, J. Engg. Fibers Febr. 2 (2007) 25.

Vien D.L., Colthup N.B., Fateley W.G., Grasselli J.G., “The Handbook of

Infrared and Raman Characteristic Frequencies of Organic

Molecules”, Academic Press, San Diego (1991).


116

Wallace G.G., Spinks G.M., Maguire L.A.P.K., Teasdale P.R., “CONDUCTIVE

ELECTROACTIVE POLYMERS-Intelligent Polymer Systems” CRC

Press, Taylor & Francis Group, Boca Raton, FL (2009).

Wang H., Xu P., Meng S., Zhong W., Du W., Du Q., “Poly(methyl

methacrylate)/silica/titania ternary nanocomposites with

greatly improved thermal and ultraviolet-shielding properties”,

Polymer Degradation and Stability 91 (2006) 1455.

Ward Y. and Mi Y., “The study of miscibility and phase behaviour of

phenoxy blends using Raman spectroscopy”, Polymer 40 (1999)

2465.

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