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|Title:||Conducting polymers and polymer electrolytes.|
|Authors:||Schlindwein, Walkiria Santos.|
|Presented at:||University of Leicester|
|Abstract:||Polymers are mostly used as insulator materials. Since the late sixties, two new classes of polymeric materials possessing either ionic or electronic conductivities have been extensively studied. The work carried out in this thesis concerns of the study of polymer electrolytes based on poly(ethylene oxide) (PEO) complexed with divalent salts (ionic conductors) and polypyrroles (PPy) electrochemically and chemically prepared (electronic conductors). Different techniques were used to study their properties including Differential Scanning Calorimetry (DSC), Variable Temperature Polarising Microscopy (VTPM), Extended X-ray Absorption Fine Structure (EXAFS), a.c. Impedance, Cyclic Voltammetry, and Fourier Transform Infra-Red Spectroscopy (FTIR). Water-cast films of PEOn:ZnX2 (X = C1, Br, I) were prepared at a range of stoichiometries. The effects of either residual presence of water or thermal treatment related to the formation of high melting crystalline materials were investigated. The morphology of the zinc halides films differs from similar films cast from acetonitrile/methanol mixtures. The presence of high melting crystalline material in the water cast samples is influenced mostly by the concentration, type of anion and drying procedure applied to the samples. The high melting crystalline materials in the zinc samples are more affected by the drying regime. In some cases, solvent effects can be removed by using a high temperature (e.g. 180°C) drying regime. The presence of water normally depresses the melting temperature of the crystalline structures. Films of PEOn.:CaBr2 and PEOn:NiBr2 cast from water were also examined. The high melting crystalline materials in the calcium samples are more affected by the presence of water. The nickel samples are highly crystalline and the presence of high melting material does not seem to be influenced by either the presence of solvent or the drying procedure. EXAFS was used as a suitable technique to probe the local structure surrounding the cation. The results of the zinc halide samples gave some indication of the interionic and polymer-cation interactions. It was demonstrated that the halogen provides the most substantial contribution for the total EXAFS spectrum and the oxygen contribution is much less significant, except in the case of PEOn:ZnC12 samples. This could be due to the size of the nearest neighbour atoms and/or to the interaction polymer-cation. The presence of neutral "ion pairing" is suggested for the PEOn:ZnBr2 samples. The EXAFS results for the samples containing NiBr2 indicated a strong interaction between polymer-salt and the local structure was dependent on concentration, unlike the zinc samples. The polymerisation of pyrrole was investigated by using chemical and electrochemical oxidation routes. The structural characterisation of the compounds obtained was limited by their insolubility. The electrochemically prepared samples presented higher conductivity than the ones which were chemically prepared. The EXAFS results at the Fe K-edge of the PPyFeCl4 sample, which was prepared by direct chemical oxidation, suggested that the iron is coordinated to oxygens at a distance 1.97 A, chlorines at 3.08 A and perhaps nitrogens at 3.72 A. The iron local structure of the composite PVA/PPy doped with FeCl3 was different from the PPyFeCl4 sample. The iron in the composite sample was coordinated to oxygens at 1.98 A and chlorines at 2.18 A. Alternatively, the presence of a distorted FeCl4- is considered.|
|Rights:||Copyright © the author. All rights reserved.|
|Appears in Collections:||Theses, Dept. of Chemistry|
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