Year

1993

Degree Name

Doctor of Philosophy

Department

Department of Chemistry

Abstract

Recent interest in investigating the chemical interactions that occur at new materials, such as conducting polymers, has been limited by the few suitable in-situ characterization techniques that are available. The primary objective of this thesis was to address this deficiency by using existing, and developing new, techniques to investigate the chemical properties of polypyrrole and polyaniline. The two main techniques used were Wilhelmy's plate technique and inverse thin layer chromatography.

Wilhelmy's plate technique measures dynamic contact angles and was useful for comparing the total interaction that occurs between the conducting polymer interface and water. Information on the wettability of the polymer surface and the adhesion of water at the interface was obtained by comparing the advancing and receding contact angle values, respectively, for polymers that had been prepared under various conditions. Polypyrrole proved to give the most interesting results, with the effects of the addition of different functional groups to the monomer, of using different substrates, of the substrate pretreatment methods, of the counterion species incorporated into the polymer and of the electrochemical polymerization methods on the properties of the polymer interface being studied. Observations were also made on the operational and interpretative aspects of the technique.

Inverse thin layer chromatography with conducting polymer stationary phases was developed. Electrochemically deposited polyaniline was found to be the most appropriate and was used in a detailed study. A method for detecting the presence of amino acids, which were used as molecular probes because they undergo a variety of chemical interactions, was also developed in this project. Inverse chromatography enables the relative strengths of different chemical interactions to be measured by comparing the retention of the molecular probe species. This indicates any inherent selectivities that the polymer may possess. A range of mobile phases were also used in order to investigate the change in the chemical interactions under varying conditions. Anion exchange interactions were found to be the strongest on the polyaniline.

Inverse thin layer chromatography was also used with an electrochemical chromatography approach in order to determine the effect of applying a potential on the chemical properties of polyaniline. A very interesting result was observed in which the anion exchange properties of polyaniline were found to decrease in strength with the application of a reducing potential, and increase in strength with the application of an oxidizing potential, in a manner that was close to being linear with the applied potential. A mechanism for this was proposed in which the density of positive sites on the polyaniline backbone varied with the applied potential as a result of the combination of unusual features of the electrochemical cell and the restriction of counterion movement through the inner layer of polyaniline.

Molecular imprinting was also investigated, with polypyrrole as the test material. No direct evidence was able to be obtained for the occurrence of this interaction. A number of techniques for characterizing this interaction were used and reasons why they were unsuccessful were suggested. Inverse high performance liquid chromatography was proposed as the most suitable method and an experimental approach was outlined, based upon the molecular probe approach.

Overall, the results presented in this thesis have provided a useful foundation for further investigations into the in-situ characterization of chemical interactions that occur on conducting polymers. This work, and that which follows it, will benefit the development of applications that make use of conducting polymers which seem destined to play an important part in many new technologies.

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