SANS investigations of oxide gel formation in inverse micelle and lamellar surfactant systems

The mechanisms of oxide gel formation in inverse micelle and lamellar surfactant systems have been investigated by Small Angle Neutron Scattering (SANS). In the first of these processes colloidal particles and gels are formed by the controlled hydrolysis and condensation of metal alkoxides in a reversed microemulsion system (water in oil), where the water is confined in the microemulsion core. With this route the rate of formation and structure of the oxide gel can be controlled by appropriate choice of the surfactant molecule (e.g. chain length) and the volume fraction of the micelles dispersed in the continuous organic phase. Investigations have been made with the system cyclohexane/water/C8φEx, where C8φEx is the non-ionic surfactant octylphenyl polyoxyethylene. The influence of the size and structure of the microemulsion has been studied by contrast variation (using deuterated solvents) before and during the reaction to form zirconia gels, and the mechanism of gelation is analysed in terms of percolation of fractal cluster aggregates. The structure of gels formed in surfactant/water lamellar phase systems, using surfactants with greater chain length, has also been investigated by SANS. The application of contrast variation to study such anisotropic bilayer systems, in which oriented gel films can be formed, is illustrated.