A STUDY OF OPTICAL ABSORPTION OF POLYANLINE THIN FILMS PREPARED BY CHEMICAL BATH DEPOSITION (CBD) METHOD

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International Journal of Advanced Research in Engineering and Technology
(IJARET)
Volume 7, Issue 2, March-April 2016, pp. 109–117, Article ID: IJARET_07_02_011
Available online at
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Journal Impact Factor (2016): 8.8297 (Calculated by GISI) www.jifactor.com
ISSN Print: 0976-6480 and ISSN Online: 0976-6499
© IAEME Publication
___________________________________________________________________________
A STUDY OF OPTICAL ABSORPTION OF
POLYANLINE THIN FILMS PREPARED BY
CHEMICAL BATH DEPOSITION (CBD)
METHOD
Kofi Owusu-Sekyere, Isaac Nkrumah, R. K. Nkum and K. Singh
Department of Physics, College of Science
Kwame Nkrumah University of Science and Technology
Kumasi, Ghana (West Africa)
ABSTRACT
The properties of Polyaniline (PANI) are very sensitive to the conditions of
synthesis and preparation techniques. Therefore, the study of the properties of
PANI with respect to different methods of preparation as well as ambient
conditions is of high importance. In this work, an attempt has been made to
synthesise polyaniline emeraldine base polymer by using oxidative chemical
polymerization method and preparation of thin films of Polyaniline on glass
substrates from Dimethyl Sulfoxide Solution (DMSO) by chemical bath
deposition (CBD) method. The glass substrates were immersed in
PANI/DMSO solution placed in a chemical bath at a temperature of 50 °C
under constant stirring for different durations. The optical absorption
measurements were carried out in order to estimate the energy band gap of
the PANI thin films prepared under different conditions.
Keywords: Polyaniline, UV-Visible Absorption, Chemical Oxidation
Methods, Thin Films
Cite this Article: Kofi Owusu-Sekyere, Isaac Nkrumah, R. K. Nkum and K.
Singh. A Study of Optical Absorption of Polyanline thin films prepared by
Chemical Bath Deposition (CBD) Method. International Journal of Advanced
Research in Engineering and Technology, 7(2), 2016, pp. 109–117.
http://www.iaeme.com/IJARET/issues.asp?JType=IJARET&VType=7&IType=2
1. INTRODUCTION
The conducting polymers are organic based polymers having the electronic properties
of semiconductors. These polymers have been found suitable for microelectronic
device fabrication due to their excellent electric characteristics and simple processing.

The most extensively studied organic polymers are polyaniline (PANI), polypyrroles,
polythiophenes, and polyphenylene vinylenes[1-2]. They have π electron
delocalisation along their polymer backbone, hence giving them unique optical and
electrical properties [1-3]. These Polymers have attracted considerable attention in the
recent years because of their reasonably good conductivity, ease of preparation and
their exceptional electrical, optical and magnetic properties. Among these polymers,
polyaniline (PANI) has emerged as a promising candidate with great potential for
practical uses such as in light emitting diodes, transparent electrodes, gas and
humidity sensing, battery applications and many more. Also, the properties of thin
films of these conducting polymers have been studied by several workers [4 -10]. In
view of this, an effort has been made to study the optical properties of PANI thin
films prepared under different conditions.
2. SYNTHESIS OF PANI [EMERALDINE SALT]
1 M of HCl was prepared by adding 83.5 ml of 36% HCl to about 600 ml of distilled
water in a 1 L measuring cylinder and making it up to 1 L. Again 12.3 g (– 0.054 mol)
of Ammonium peroxydisulphate [(NH4 )2 S2 O8 ] was dissolved in 70 ml of 1 M HCl
in a 500 ml beaker and kept at room temperature. The Aniline Hydrochloride was
prepared by using 5 g (– 0.054 mol) of Aniline in 75 ml of 1 M HCl in another 500 ml
beaker and that was also kept at room temperature. Both solutions, the Aniline
Hydrochloride and [(NH4)2 S2 O8] were mixed together in a drop wise fashion over a
period of about 20 minutes. After few minutes, it was observed that the solution
started taking on a blue-green color and then became intense blue green with a copper
tint. The solution was constantly being stirred with a magnetic stirrer. The solution
was left at room temperature for 24 hrs for polymerization to complete. The solution
was then washed with distilled water under filtration with a filter paper and the
precipitate was collected in a beaker.
3. PREPARATION OF PANI [EMERALDINE BASE]
The prepared emeraldine salt (powder form) was taken in a round-bottomed flask
containing 20 ml of ammonia solution and 80 ml of water, and was stirred
continuously for 24 hrs. The precipitated blue emeraldine base was filtered and the
precipitates was collected and dried under dynamic vacuum at 70 o
C for 15 hrs.
4. PREPARATION OF THIN FILM ON GLASS SLIDES
0.5 g of the emeraldine base (powder form) was mixed with 10 ml of DMSO in a
beaker and left to dissolve for 24 hrs. The emeraldine base solution was filtered and
the filtrate was collected. Thoroughly cleaned glass substrates were suspended for 5
min, 10 min, and 12 hrs in the beaker placed in a chemical bath at a temperature of 50
°C. Constant stirring was performed using a magnetic stirrer to ensure uniform
distribution and deposition. The glass substrates were taken out and washed with
distilled water. The samples were dried at room temperature for few hours and the
optical absorption measurements were carried out in order to estimate the energy band
gap. In order to estimate the band gap after heat treatment, the samples were annealed
for 30 minutes at 45 0
C.
5. UV-VIS SPECTRA OF PANI
The optical absorption measurements were carried out in order to analyze the
absorption bands and estimate the optical band gap of Polyaniline Emeraldine base

A Study of Optical Absorption of Polyanline thin films prepared by Chemical Bath
Deposition (CBD) Method
thin films prepared on glass slides under different conditions. After measuring the
optical absorbance (A) of all the samples as a function of wavelength ( λ), the
absorbance (A) were plotted as a function of wavelength to observe the possible
transitions at different wavelengths.
The energy band gaps of PANI thin films were determined by the absorbance
spectra using the following relation:
A =
Where, υ = frequency
h = Planck’s constant
n = type of transition
k = transition probability constant
Eg is the energy gap, hυ is the photon energy. In order to determine the optical
energy band gaps, the graph of (Ahυ )2
versus hυ were plotted by replacing n = 1
which was allowed for direct transition. The extrapolation of the straight line to
(Ahν)2
= 0 to the photon energy axis gives Eg.
6. RESULTS AND DISCUSSION
Figures 1 -3 show the absorbance of the thin films for deposition times of 5 min, 10
min and 12 hours which are represented by A1, A2 and A3 respectively. In Figs 1 and
2 the band observed between 300-360 nm for the PANI samples corresponds to π →
π* transitions, and also a high extensibility and reversibility between 750-850 nm in
case of sample A1. Figs. 2 and 3 show absorption peaks at about 450 and 540 which
corresponds to the polaron and bipolaron band transitions for polyaniline [11-15].
Figs 4-6 show the plots of (Ahν)2
versus hν and the values of Eg obtained about 2.5
eV. The effect of heat treatments on band gap energy were studied and the summary
of the results were shown in Figs.7-9.
Figure 1 Absobance vs wavelength of PANI thin film (Sample A1)

Figure 4 (Ahν)2
vs hυ of PANI thin film (Sample A1)
Figure 5 (Ahν)2

Figure 6 (Ahν)2
Figure 7 (Ahν)2
vs hυ of PANI thin film ( Annealed sample A1)

Figure 8 (Ahν)2
vs hυ of PANI thin film ( Annealed sample A2)
Figure 9 (Ahν)2
vs hυ of PANI thin film (Annealed sample A3)

7. CONCLUSION
In this work, the optical characteristics of PANI thin films prepared under varying
times for deposition on glass slides using simple chemical bath deposition method
have been reported. The absorption peaks obtained between 300 and 360 are found to
be related to π – π* electronic transitions in PANI. Whereas, the peaks obtained at
about 450 and 540 are due to polaron and bipolaron band transitions. Also the values
of band gap estimated for different samples after annealing confirm the successful
deposition and solidity of PANI films on glass slides using CBD method.
ACKNOWLEDGEMENTS
The authors would like to thank the Head of Physics Department, College of Science,
KNUST for making available the required chemicals and reagents used for this work.
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