1 of PVP[8] 2 Experimental 2.1 Materials Aniline

1         
Introduction

Now-a-days, conductive polymers are
greatly used in various applications like light-emitting diodes, batteries,
electromagnetic shielding, antistatic coating, gas sensors etc. Conducting
polymers are combined with other insulating polymers that are good at
mechanical properties. Polyaniline is preferred over other conductive polymers
because of its stability, low raw material cost and ease of synthesis 1.
It was discovered by Runge in 1835 and initially called aniline black. It
consists of reduced benzoid rings and oxidized quinoid rings. There are three
oxidation states of polyaniline namely leucoemeraldine (fully reduced),
pernigraniline (fully oxidized), emeraldine base (half oxidized) 2.

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Figure 1 Different oxidation states of
polyaniline (y = 1: leucoemeraldine, y = 0.5: emeraldine and y = 0: pernigraniline2

Due to infusibility and insolubility,
PANI is difficult to process. In order to improve its processibility, PANI is
doped with organic acids having long non-polar tails like dodecylbenzene
sulfonic acid (DBSA) and camphor sulfonic acid (CSA). This makes polyaniline
soluble in many organic solvents such as chloroform, m-cresol and xylene. This
also makes possible the solution processing of polyaniline with other polymers
3. Polyaniline requires polaron state to be electrically conducting. For this
purpose, organic dopants such as dodecylbenzene sulfonic acid (DBSA), sodium
dodecyl sulfonate (SDS), sodium dodecylbenzene sulfonate (DBSNa), Tetra-decyl-tri-methyl-ammonium
bromide (TTAB), sodium bis (2-ethylhexyl) sulfosuccinate (AOT) and inorganic
dopants such as HCl, H2SO4, HBF4, H3PO4, CrO3 etc. are used 4,5.

Poly vinyl pyrrolidone (PVP) also called
Povidone and it is the polymer of vinyl pyrrolidone. Because of its outstanding
absorption and complexes abilities; like PVP added to iodine forms complex
called povidone-iodine that possesses disinfectant properties due to the
presence of iodine, a bactericidal component thus it has been extensively used
in pharmaceutical, cosmetic and food industry as well as in various technical
applications 10. PVP is water soluble polymer and hygroscopic in nature and
has good thermal stability. In solution it has excellent wetting properties and
readily forms films so this makes it good as a coating.  Due to its high polarity it binds
exceptionally well to polar molecules. Adhesive and cohesive properties are
also good. It is soluble in polar solvents and also dissolved in various
organic solvents and insoluble in esters, acetone, ethers, ketones and
hydrocarbons 10.

Figure 2 Structure of PVP8

2         
Experimental

2.1       
Materials

Aniline (DAEJUNG), dodecylbenzene sulfonic acid
(DBSA; DAEJUNG),  acetone, distilled
water, ammonium persulfate (APS; Riedel deHaen), hydrochloric acid (HCl;
Scharlau), polyvinylpyrrolidone (PVP K 30; DAEJUNG), N methyl-2-pyrrolidone
(NMP;LAB-SCAN), chloroform (Riedel deHaen), xylene (DAEJUNG), ethylene glycol
(DAEJUNG),N,N-Dimetylformamide (DMF; DAEJUNG), m-cresol (Scharlau).

2.2       
Preparation of the PANI/DBSA powder

Aniline (8 g) was mixed with 22 g DBSA and 400 ml
distilled water. Use magnetic stirrer to form a homogeneous milky white
dispersion of anilinium-DBSA complex. Under constant stirring, the dispersion
was cooled to 0~5 0C. The APS solution (20 g APS in 100 ml water)
was pre cooled to 0~5 0C and then added into milky solution drop
wise. The milky solution turns into dark green. To terminate the polymerization
add the 100 ml acetone, it will not only terminate the polymerization but also
decrease the viscosity and remove the extra DBSA. After this filtrate the
sample and wash with distilled water several time until the filtrate was
colorless and dry in oven for 48 hr at 500C.

2.3       
Preparation of PANI-HCl

Prepare 1M solution of aniline in 1M HCl. Use the
magnetic stirrer to form a homogenous solution. During the stirring keep the
temperature of reaction 10C. Prepare the 0.25 M solution of APS in
de-ionized water and pre cooled it at 10C for 1 hr. Add the APS
solution drop wise and sample turns into dark green color. After 3 hr, filter
the sample and wash it with distilled water for several times until the
filtrate obtained was colorless, then dry the sample at 500C for 1
day.

2.4       
Preparation of blend

5g PVP and 0.1 g PANDB were added into chloroform
(60 ml) at room temperature. Keep on stirring until a homogeneous and viscous
solution formed, then poured the sample on glass substrate. The evaporation of
solvent was carried out at 40 0C for 72 hr.

2.5       
PVP film casting

PVP
films were synthesized in different solvents (distilled
water (1000C), N methyl-2-pyrrolidone (2020C; NMP),
chloroform (61.20C), xylene (138.40C), ethylene glycol
(197.30C), ethanol (78.370C), methanol (64.70C),
dimetylformamide (1530C; DMF) and m-cresol (202.80C), to
obtain a flexible film. Films obtained by all these solvents were brittle
except NMP.

3         
Characterization

3.1       
TGA analysis (TGA)

Themogravimetric
analysis was conducted to measure the weight loss of samples. Thermograms were
obtained by using Shimadzu TA-60 in temperature range of 20-600 oC
with heating rate 10 0C/ min under nitrogen atmosphere. The weight
losses of all samples were analyzed at different stages.

3.2       
DSC thermal analysis (DSC)

Differential scanning calorimeter was used to study
the thermal properties of samples. The glass transition temperature of samples
were obtained by using Shimadzu DA-50 with scan rate of 10
0C/ min and temperature range from 20-250oC.

3.3       
Fourier transform infrared spectroscopy (FTIR)

FTIR spectra of samples were obtained by Alpha FTIR with
computer software. The characterization was performed in 4000-600 cm-1
wave number. Formation of hydrogen bonding and interaction
between the elements in (PANI-DBSA) and its blend was investigated by Fourier
Transform Infrared Spectroscopy (FTIR).

4         
Results:

4.1       
FTIR:

Figure 3 FTIR spectra of PANI/HCl,
PANI/DBSA and PANI/PVP blend

 FTIR analysis
shows the nature and extent of interaction between polymers. Mixing at
molecular level resulted into the change in peaks. FTIR shows the Quinoid ring and benzoid ring at 1574cm-1
and 1488cm-1 respectively, C-N+. Stretching 1235cm-1,
NH+= bending 1128cm-1 in PANI doped with HCl 7.

In PANI doped with DBSA, Quinoid ring 1542cm-1 and benzoid ring 1460cm-1, NH+= bending 1086 cm-1
are identified by FTIR 6.

In PANI/DBSA-PVP blend, hydrogen bonding is developed
between Carbonyl stretching (C=O) band of PVP and NH+– of the PANI.The Carbonyl stretching band of PVP is
shifted at 1652cm-1 on the addition of 10% PANI from 1660cm-1.
Quinoid and Benzoid rings are identified at 1574cm-1 and 1488cm-1
respectively 7.

4.2       
DSC Analysis:

DSC curves are obtained by the using
DA-50 which gives the information about glass transition temperature Tg.

Figure 4 DSC spectra of PANI/HCl, PANI/DBSA
and blend

DSC curves provide the information about glass
transition temperature.

PANI doped with HCl showed the endothermic peak is
at 122.71oC while PANI doped with DBSA showed the 133.55oC
12.

Pure PVP shows the Tg at 162.3oC 3.

PANI doped with DBSA blended with PVP shows the Tg
at 153.75oC 3.

4.3       
TGA Analysis:

Thermo
gravimetric analysis was carried out using TA-60 Shimadzu in a temperature
range of 15-600oC. TGA curves of PANI doped with organic acid
“Dodecylbenzenesulphonic acid” (DBSA) and inorganic acid i.e. HCl and PANI-DBSA
blended with PVP are shown in the given below. Three major stages are obtained
in Thermogrames.

 

Figure 5 Thermograms of PANI/HCl, PANI/DBSA
and blend

 

At 100oC, moisture is evaporated. The
second weight loss is associated with the destruction of linkage between NH+—SO-3
and PANI chain in a temperature range of 320-370oC and the third
weight loss is associated with the degradation started about 410-460oC
9.

In case of HCl doped PANI, first weight loss is
associated to the volatility of water that is absorbed by the polymer in the
form of moisture in between 60-110oC about 23%. In second stage,
weight loss is attributed to dopants or smaller oligomer chains, started at 358oC
and finally the decomposition of main chain of polymer at 568oC 10.

Similarly in PANI/PVP blend, the weight loss of
moisture is upto 100OC. the decomposition temperature of blend is higher
than the PANI-DBSA i.e. about 402-432oC. After that PANI chain is
started to decompose at 432oC 11.

5         
Conclusion

Conductive
blend of polyaniline doped with dodecylbenzene sulfonic acid (PANI-DBSA) and
polyvinylpyrrolidone (PVP) was prepared. Thermal characterization was carried
out by using DSC, TGA and FTIR. To obtain the conductivity and flexibility, PVP
films were synthesized in different solvents. a comparative study of effect of
PVP grades and effect of solvents on the properties of blend will be carried
out in next term. 

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