Acid and base effects on the morphology of composites formed from microemulsion polymerization and sol-gel processing

Phase behaviour studies were performed for microemulsions, containing organic monomers (methyl methacrylate and acrylic acid), inorganic monomer (tetraethoxy silane (TEOS)), a cross linking agent (ethylene glycol dimethacrylate) and water, stabilized by a cationic surfactant, cetyltrimethylammonium bromide. Single phase transparent microemulsions were formed over a considerable portion of the composition domain. The effects of an acid, hydrochloric acid (HCl), and a base (NH4OH) on the gel times were studied and the catalytic action of acid and base on the overall set-gel reaction was analysed. Organic/inorganic polymer composites were obtained from the hydrolysis and polycondensation reactions of TEOS (sol-gel process) and polymerization of organic monomers and inorganic monomer containing microemulsions. Scanning electron microscopy was used to examine the surface morphology of the composites. For the acid and base studies a precursor microemulsion with pH 7.0) exhibiting closed-cell microstructure upon polymerization was selected. The morphology was examined for polymerized microemulsions with the same base composition but with varying HCl to TEOS ratios or NH4OH to TEOS ratios. Pore continuity and morphology are strongly influenced by the presence of acid or base. Both the HCl and NH4OH containing precursor microemulsions led to open celled porous composites.