CHARACTERIZATION OF WATER-IN-OIL MICROEMULSIONS FORMED IN SILICONE OILS

The phase stability and structure of water-in-oil microemulsions stabi lized by the surfactant Aerosol OT have been examined in the low molec ular weight silicone oils hexamethyldisiloxane (HMDS) and diphenyltetr amethyldisiloxane (DPTMDS). Title solubilization capacity omega(max) ( where omega = [H2O]/[AOT]) determined as a function of temperature def ines a limited single phase microemulsion region with relatively low w ater solubilization (omega(max) < 40). Addition of NaCl shifts this si ngle phase region to a higher temperature. SANS and dynamic light scat tering measurements show the presence of strong attractive interdrople t interactions in HMDS, which are relatively absent in DPTMDS. Additio n of n-octanol as a cosurfactant dramatically increases the solubiliza tion of water in HMDS, giving an optimal solubilization capacity at a specific cosurfactant:surfactant molar ratio, x. Small-angle neutron s cattering (SANS) measurements made close to the optimized condition sh ow elimination of attractive interactions. A Porod analysis of the SAN S data demonstrates an increase in the area of the surfactant/cosurfac tant layer and commensurate reduction in droplet size with increasing x.