What is so special about aerosol-OT? 2. Microemulsion systems

The aim was to identify why Aerosol-OT is such an efficient surfactant for forming microemulsions, and in pursuit of this, 11 Aerosol-OT-related compo unds have been investigated. These surfactants were from two separate homol ogous series, with either linear or branched hydrocarbon tails. Hence, it w as possible to examine the effect of chain structure on packing in curved i nterfacial films at oil - water interfaces. With the linear dichain compoun ds, water-in-oil microemulsion phases could be formed only in the presence of a short-chain alcohol. On the other hand, all the branched surfactants f ormed microemulsions without cosurfactant. Within the range of structures s tudied, it was possible to identify a minimum branching necessary to stabil ize a ternary microemulsion. With branched sulfosuccinates the single-phase microemulsion region only differed by its location on the temperature scal e, and this was correlated with subtle variations in hydrophobicity, caused by the different chain structures. Small-angle neutron scattering was used to characterize the microemulsion aggregates and adsorbed films. Packing a t the oil-water interface, and the water droplet radius, was shown to be re lated to chain architecture, and the same pattern of behavior was found as at the air-water interface (see the preceding paper in this issue). Therefo re, with regard to microemulsion formation Aerosol-OT is no special case, b ut it possesses a chain structure that gives optimum aqueous-phase solubili ty around room temperature.