Year

1995

Degree Name

Doctor of Philosophy

Department

Department of Chemistry

Abstract

Conducting polymers have in the past been plagued by either poor environmental or poor thermal stability. Indeed, many of the applications envisioned for these materials require a high level of conductivity, thermal and environmental stability. In all these applications, the long-term stability of the polymer determines the limits of its use. This stability is then assessed in terms of the property of interest, such as: conductivity, electroactivity, chemical or mechanical properties.

The present work is concerned with thermal studies based on polypyrrole and polyaniline conducting polymers. The effect of exposing conducting polymerss to elevated temperatures on the electroactivity and conductivity of the polymers has been considered.

Polypyrrole conducting polymers were prepared as coated electrodes or free standing films, then the effect of thermal treatment on the electrochemical or electrical conductivity was investigated in different media. It was found that the redox properties and conductivity could be improved with mild heating but degraded at higher temperatures.

In all cases, it was found that the nature of the dopant plays the greatest role in determining the stability of Polypyrrole conducting polymers at elevated temperatures.

In the application part of this project polypyrrole films were prepared as free standing films or membranes. The effect of solution temperature on the transport properies of these polymers which are based on their unique electrochemical properties was investigated. It was found that PPy membranes doped with small mobile counterions show higher transport of ions at low temperatures. By contrast, the PPy membranes doped with immobile counterion showed higher flux at elevated solution temperatures.

Cyclic voltammetry, quartz crystal microbalance, and resistometry techniques, have been employed to study the effect of solution temperature on the properties of polypyrrole films.

It was also found that dry state thermal treatment of polypyrrole membranes under appropriate conditions, in spite of improving the conductivity or electroactivity, did not result any improvement in the transport properties of the polypyrrole membranes.

Polyaniline films were also coated on electrodes by chemical and electrochemical means in order to investigate the thermal stability of the electroactivity in air and nitrogen atmospheres. Polyaniline was also synthesised chemically and cast as a membrane. It was found that the electroactivity and conductivity of the films was stable up to 150°C. Exposure to higher temperatures leads to a decrease in electroactivity and conductivity, although use of a nitrogen atmosphere has less effect on the properties than air.

It was found that the electrochemical cell developed in our research laboratory for transport studies can be easily used for in-situ characterisation of conducting polymer membranes. Using this cell setup, allows a wide range of electrochemical techniques to be used for characterisation of conducting polymers that can be prepared as free standing films.

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