ADSORPTION AND AGGREGATION OF SODIUM BIS(2-ETHYLHEXYL) SULFOSUCCINATE IN SYSTEMS CONTAINING TOLUENE PLUS WATER, 1,2-ETHANEDIOL, OR 1,2,3-PROPANETRIOL

We have investigated the adsorption and aggregation of sodium bis(2-ethylhexyl)sulfosuccinate (AOT) in mixtures containing toluene as oil phase and either water, 1,2-ethanediol (ED), or 1,2,3-propanetriol (PT) as the polar phase. Replacement of water by either ED or PT leads to a reduced tendency for adsorption at the oil-polar phase interface and for aggregate formation. In the case of ED as the polar component, there is substantial partitioning of the AOT to the toluene phase at concentrations below the critical aggregation concentration (cac). Over this concentration range, AOT in the toluene phase shows highly nonideal behavior consistent with extensive and progressive surfactant association below the cac. Polar phase cac values are increased by factors of approximately 20 and 800 in changing from water to PT and ED, respectively. Addition of NaCl to the polar phases causes a Winsor I-III-II progression of phases with concomitant changes in the post-cac oil-polar phase interfacial tensions and surfactant distribution. The NaCl concentrations required for microemulsion phase inversion increase in the sequence water < PT < ED. Macroemulsions formed by emulsification of the multiphase Winsor systems show inversion of emulsion type at similar NaCl concentrations to those required for the corresponding microemulsion phase inversion.