ESR INVESTIGATIONS ON THE STABILIZATION OF ALUMINA DISPERSIONS BY AEROSOL-OT IN DIFFERENT SOLVENTS

Dispersions in organic liquids are used to produce a number of product s, such as high-performance ceramics, magnetic tapes, inks, paints and pigments. In this study, the stabilization of colloidal alumina by an anionic surfactant, Aerosol-OT (AOT), in solvents of different polari ty was investigated. It was found that in the absence of a dispersant, as the solvent polarity is increased the dispersion stability goes th rough a maximum. The presence of AOT alters the stability of dispersio ns in low and high dielectric constant solvents, but not those in mode rately polar liquids. The latter is shown to be mainly due to the lowe r adsorption of AOT on alumina from these solvents. Changes in surfact ant orientation at the solid-liquid interface in different solvents we re also monitored by electron spin resonance (ESR) spectroscopy using adsorbed and chemically bonded 7-doxylstearic acid probes. The results clearly show that surfactant orientation and packing at the interface vary with solvent polarity and a compact adsorbed layer is required t o obtain enhanced stability in the presence of surfactants.