Factors affecting the conductivity of surface immobilised polyaniline
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Date
1998-11-07
Authors
Wickramanayake, D. K. W. W. M. S.
Rajapakse, R. M. G.
Journal Title
Journal ISSN
Volume Title
Publisher
University of Peradeniya
Abstract
Polyaniline exists in six different structural forms depending upon the extent of
oxidation and protonation of the polymer backbone. One of these forms is an electronic
conductor with maximum recorded conductivity of 100 S cm-I. Some of these forms
can be easily and quickly interconverted while the most oxidised form is prone to
various chemical reactions leading to the degradation of the polymer. The extent of
conductivity of the conducting form of the polymer, known as emaraldine salt, depends
strongly on various parameters such as the acidity, the counter ion etc. The properties
of the materials are such that innumerable possible technological applications for the
material can be found. However, most of such applications depend on the processibility
of the material. We have already designed and developed a method to retain polyaniline
on ordinary glass surfaces. This involves the reaction of surface hydroxyl groups of
glass with SOCh followed by aniline at ca. 400°C and subsequent deposition of
polyaniline by oxidative polymerisation of aniline in aqueous acidic solution containing
functionalised glass plates. This procedure ensures a permanent attachment of
polyaniline on glass surfaces though the conductivity of the surface is relatively poor
owing to the discontinuity of the polyaniline layer on the surface. During this project
we have attempted to increase the smoothness and conductivity of the polyaniline coat
attached to ordinary glass surfaces by further improving the immobilisation procedure
and studying the factors affecting the conductivity of the immobilised polyaniline layer.
Ordinary silica glass surfaces contain some hydroxyl groups and Si-O-Si
linkages and bound water molecules. Refluxing the glass with concentrated
hydrochloric acid results in the hydrolysis of the Si-O-Si linkages to yield Si-OH
groups. As such pre-cleaned glass pieces were refluxed with cone. HCI for different
periods from 1 hour to 24 hours. The plates were then rinsed with water and dried. The
above procedure was then followed on such glass plates. Also the effect of
concentration ratio of the oxidant to the monomer and the effect of various oxidants
and their concentrations were studied in order to investigate the best oxidant, optimum
concentration ratio for obtaining highly conducting smooth glass plates.
Our results have clearly shown that the refulxing with cone. HCI for a minimum
of 6 hour period ensures the increased amount of surface -OH groups and hence better
contrast for the surface deposited polyaniline layer. Further, we found that Fe3+ is a
better oxidant than all the other oxidants tested ( 6 in number ranging various redox
potential values above that of aniline/aniline"). The optimum concentration ratio is 1:6
in monomer:oxidant when Fe3+ was used as the oxidant. The resultant polyaniline layer
is smooth to microscopic examination and has a sheet resistance of8.5 kQ cm-I.
Description
Keywords
Physical sciences engineering and technology , Conductivity , Surface , Polymers , Polyaniline
Citation
Proceedings & Abstracts of the Annual Research Sessions 1998, University of Peradeniya, Peradeniya, Sri Lanka, pp.103