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Chapter-2
Synthesis, Characterization & Measurement Techniques
As already mentioned in Chapter 1 (Section-1.6), the present work
is focussed on a systematic study related to the electrical, optical and
structural behaviour of PMMA-PAni blends. In this chapter, after a brief
description of PMMA, the experimental procedure followed for the
synthesis of different forms of Polyaniline (emeraldine salt) doped with
Dodecyl benzene sulfonic acid (DBSA), Camphor sulfonic acid (CSA),
Iron (Fe) and Copper (Cu), respectively has been discussed. Next, the
method adopted for the preparation of PMMA-PAni blends on mixing
the synthesized PAni in PMMA at various concentrations has been
presented. Thereafter, various characterization techniques, like UV-
Visible Spectroscopy (UV-VIS), Fourier Transform Infrared (FTIR)
Spectroscopy and Raman Spectroscopy, used in the present study for
characterizing PAni and PMMA-PAni blends, have been described.
Finally, a brief description regarding the Current-Voltage (I-V) and
dielectric measurements related to these blends is presented.
2.1 POLY(METHYL METHACRYLATE)
Poly(methyl methacrylate), generally named as PMMA and having
the monomer composition C5H8O2, is a linear, amorphous,
Ph.D. Thesis: A.K. Tomar-2012
46
thermoplastic polymer with high transparency in almost entire visible
range [Mark et al. 1985; Hong 2001; Leontyev 2001; Tatro et al.
2003; Hadjichristov et al. 2009; Lin 2010]. Due to this extraordinary
feature, it is sometimes referred to as acrylic glass. The chemical
structure of this polymer is as shown in figure 2.1 [Billmeyer 2005].
Figure 2.1: Chemical structure of Poly(methyl methacrylate)
Some of the important physical parameters of PMMA [Wunderlich
1975; Billmeyer 1984; Stobl 1997; Brandrup et al. 1999; Mark 1999]
are listed below:
Density : 1.17-1.20 g/cm3
Optical Energy Gap : 2.72 eV
Refractive index : 1.49
Glass transition temperature (Tg) : 105 0C
Melting point : 160 0C
Working temperature Range : -40 0C to +90 0C
Dielectric constant (at 1 MHz, 250 C) : 2.6
Dissipation Factor : 0.04-0.06
Resistivity : >1015 Ωcm
Thermal Conductivity : 0.193 Wm-1K-1
Water absorption : 0.3-0.4%
It is extraordinarily resistant to oxidative photodegradation
[Hawkins 1972], remarkably stable to sunlight [Benfor and Tipper
1975] and displays good environmental stability [Billmeyer 1971]. Due
Chapter-2: Synthesis, Characterization & Measurement Techniques
47
to such extraordinary features, in addition to its scientific and
technological applications [Kuo 2003; Leontyev et al. 2003; Kulish
2003; Koval 2004; Sousa 2007; Dorranian 2009; Abdelrazek 2010;
Fawzy 2011]; this polymer is widely being used in many day to day
applications.
2.2 SYNTHESIS OF POLYANILINE
Different forms of Polyaniline (Emeraldine Salt) doped with Dodecyl
benzene sulphonic acid (DBSA), Camphor sulphonic acid (CSA), Iron
(Fe) and Copper (Cu) salts, have been synthesized chemically using
oxidative polymerization method [Chen 2002]. The reactions were
carried out at low temperature below 10 0C, to get PAni with high
molecular weight [Macdiarmid et al. 1985; Arms and Miller 1988;
Austrias et al. 1989; Cao et al. 1989; Genies et al. 1990; Kricheldorf
1992; Kang et al. 1995; Mav et al. 1999; Vijayan and trivedi 1999; Xie
and Xiang 2000; Rao et al. 2001; Chen 2002; Negi and Adhyapak
2002]. The details of the procedure adopted are as follows:
2.2.1 Polyaniline Doped with DBSA (PAni.DBSA)
PAni.DBSA has been synthesized from aniline using DBSA as
dopant and ammonium persulphate (APS) as oxidant. The molar ratio
of aniline:DBSA:APS was kept as 1:1:1. First, the prepared milky white
solution of aniline and DBSA (70 weight % in 2-propanol) in deionized
water was stirred magnetically in ice-cooled environment and then, the
precooled solution of APS was added to it dropwise, resulting in change
in the colour of the solution from milky white to green. The so obtained
viscous solution was kept at low temperature (below ~10 0C) for 24
hours. Subsequently, acetone was added to this solution to decrease
its viscosity and favouring precipitation. This dispersion was filtered
and the residue was washed repeatedly in deionized water till the
filtrate became colourless. Then, the obtained powder was dried in
vacuum oven at 70 0C for 48 hours. Finally, a dark green powder of
PAni.DBSA was obtained.
Ph.D. Thesis: A.K. Tomar-2012
48
2.2.2 Polyaniline Doped with CSA (PAni.CSA)
For the synthesis of PAni.CSA, the monomer (aniline), CSA as
dopant and APS as oxidant were used in the molar ratio of 1:1:1. The
cooled solution of APS in deionized water was added dropwise in the
precooled transparent aqueous solution of aniline-CSA with continuous
stirring. The obtained clear solution was kept at low temperature for
24 hours, resulting dark green suspension, which was filtered,
repeatedly washed and dried in vacuum for 48 hours giving the dark
green powder of PAni.CSA.
2.2.3 Polyaniline Doped with Fe Salt (PAni.Fe)
To synthesize PAni.Fe, the greenish brown solution of aniline and
FeCl3, prepared in deionized water, was allowed to cool in ice-cooled
environment under stirring. The molarity ratio of aniline:FeCl3:APS
was kept as 1:1:1. Afterwards, the cooled APS solution in deionized
water was put drop by drop in the above prepared solution of aniline-
FeCl3. After 24 hours of constant cooling followed by filtration, washing
with deionized water and finally, on drying in vacuum oven for 48
hours, the dark green powder of PAni.Fe was obtained.
2.2.4 Polyaniline Doped with Cu Salt (PAni.Cu)
For the synthesis of PAni.Cu, aniline and CuCl2 were dissolved in
deionized water and a greenish coloured solution was obtained. The
precooled solution of APS in deionized water was added in the
prepared aniline-CuCl2 solution dropwise and a dark bluish solution
was resulted. The molarity ratio of aniline:CuCl2:APS was kept as
1:1:1. After the 24 hours of cooling, this solution was turned to dark
green suspension, which on filtration followed by washing with
deionized water and drying in vacuum oven, resulted in a dark green
powder of PAni.Cu.
In order to confirm the characteristics of prepared PAni powders
having different dopants, the same were subjected to UV-Visible, FTIR
and Raman spectroscopy. Their conduction and dielectric behaviour
was analysed using V-I and dielectric measurements. Afterwards, to
Chapter-2: Synthesis, Characterization & Measurement Techniques
49
make the blends of as prepared PAni with PMMA, the PAni salts were
mixed with PMMA at different concentrations by weight following the
procedure, as discussed in the next section.
2.3 PREPARATION OF PMMA-PANI BLENDS
The blends of PMMA with different weight % of PAni.DBSA,
PAni.CSA, PAni.Fe and PAni.Cu were prepared through solution casting
method by dissolving the as-prepared PAni (ES) powder at varying
concentrations in PMMA taking Chloroform as solvent. The prepared
blended solutions were put to glass petri-dishes, which after the
evaporation of the solvent at room temperature, were converted to
PMMA-PAni blends in the form of free standing films. In order to study
the optical, electrical and dielectric response of the blends, these were
subjected to UV-Visible spectroscopy, I-V measurements, and
Dielectric spectroscopy, respectively. Further, the structural analysis of
these blends was carried out through Fourier Transform Infrared
(FTIR) and Raman spectroscopic techniques.
The following sections are devoted to the short details of various
experimental and measurement techniques, as mentioned above, in
order to reveal the induced changes in PMMA as an effect of blending
with different weight % of synthesized PAni salts, as mentioned in
Section-2.2.
2.4 UV-VISIBLE SPECTROSCOPY
Ultraviolet-Visible spectroscopy is one of the most important
analytical techniques to characterize organic compounds, especially
conjugated organic materials as these absorb energy in UV or Visible
region [Pavia et al. 1994; Banwell and McCash 1995; Zerbi 1999].
This technique is most widely used due to its simplicity, versatility,
speed, accuracy and cost-effectiveness.
2.4.1 Theory and Instrumentation
The absorption of electromagnetic radiations in the UV-Visible
region generally involves the transition of an electron between the
Ph.D. Thesis: A.K. Tomar-2012
50
electronic energy levels of the molecule[Campbell and White 1989;
Kemp 1991; Pavia et al. 1994; Banwell and McCash 1995; Campbell et
al. 2000; Gauglitz and Dinh 2003; Ho
