Feraille, Gaël (2003) Synthesis and processing of conducting polymers within the lattices of nanoporous silicas. (PhD thesis), Kingston University, .
Abstract
The following study covers the preparation and characterisation of polypyrrole silica (PPy-silica) composites exhibiting semiconducting properties (cr up to 10-3 S.cm-1) and good thermal and environmental stabilities, making them suitable materials for applications such as gas sensors, antistatic agents, etc. These materials were produced by the in situ polymerisation of pyrrole (Py) monomers within the lattices of nanoporous silicas and aluminosilicas, such as microporous synthetic zeolites (Linde A and Linde X) and mesoporous M41S silicas (MCM-41/48, H1 and V 1), using either chemical or electrochemical oxidative polymerisation. Chemical polymerisation was initiated, at 0°C, by oxidising agents (transition metal cations, ferric chloride or ammonium persulphate) pre- or post-introduced into the lattices, depending on the nature of the host. Doping was achieved by the introduction of dopant anions, mainly sulphonates (MBSA, DBSA and DEHS), during the polymerisation process. Direct threading of soluble doped polypyrrole (PPy-DEHS and PPy-DBSAex) was also attempted, but was found to irremediably result in the formation of materials, in which only the external surfaces of the host matrices were covered by layers of polymeric material. This study was split into three main parts. (i) Firstly, the synthesis and characterisation of doped polypyrrole (PPy-DBSA, PPy-MBSA) and soluble doped polypyrrole (PPy-DBSAex, PPy-DEHS) materials, produced in solution either by chemical or electrochemical oxidative polymerisation. These materials were found to exhibit semiconducting properties (10-4-30 S.cm-1) and good thermal stabilities (up to 300°C), but were sensitive to atmospheric oxygen and moisture. (ii) Then, the focus was forwarded to the selection of commercially available microporous aluminosilicas and the production and characterisation of mesoporous silicas (M41S) able to accomodate pre-synthesised polymeric chains or to allow the formation of similar chains within their pore networks. These materials were then post treated either by simple ion-exchange (synthetic zeolites) or post-synthesis functionalisation (M41S silicas) using organosilanes, such as chlorotrimethylsilane (TMS) and aminopropyltriethoxysilane (APS). Ammonia post-treatment was also attempted, but was found to be unsuccessful. (iii) Finally, PPy-silica composites and PPy-silica film composites were produced by adapting oxidative polymerisation methods, employed to produce conventional polypyrrole materials, to the confined geometry of nanoporous materials. The resulting composites exhibited insulating to semiconducting properties (10-8-10-3 S.cm-1 depending on the nature of the host, the doping agent and the oxidising agent, and good thermal stability and increased environmental stability when compared with analogues prepared in solution.
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