Preparation and characterisation of inorganic – organic hybrid materials

Abstract

By incorporating nanometre particle size titania into polymers, hybrid materials can be prepared. These materials have enhanced thermal, mechanical, optical, and electronic properties, which are often greater than what would be expected from a simple blend of the source materials. In this work the preparation of hybrids of titania with poly(vinyl pyrrolidone), nylon-6, poly(acrylic acid), poly(2-hydroxyethyl methacrylate), and gelatin are explored. Two different techniques were used: sequential processing where the nanoparticle solution and the polymer were prepared separately and mixed together and an in-situ technique, where the titania component and the polymer were generated at the same time. For the sequential hybrids, care was required to minimise solvent usage, as too much leads to residual stresses and cracking. Controlled temperature solvent removal techniques were developed to minimise cracking. For the in-situ hybrids, careful matching of the sol-gel and polymerisation kinetics was required to prevent the formation of large particle size and aggregated titania that lead to inhomogeneous final products. Acetylacetone was a suitable regulator of the sol-gel reaction, which limited the sites available for condensation and prevents large particle size and aggregates of titania forming. Conventional chemical initiators gave incomplete conversion, and so γ-radiation initiated polymerisation was used as it leads to very high monomer conversions. This is viewed as a novel aspect with no reports currently in the literature that show hybrids prepared in this manner. A range of PHEMA-titania hybrid hydrogels were prepared in this way. Polymer derived titania chars were prepared by pyrolysing the polymeric component of hybrids. The heating rate and the final temperature of pyrolysis were determined as key variables that affect the structure and morphology of the char. The microstructure of the hybrid was also found to have some influence on structure. Some polymer degradation of the hybrids resulted from titania addition.