MICROSTRUCTURES OF CONCENTRATED WATER-IN-OIL MICROEMULSIONS IN SODIUM BIS(2-ETHYLHEXYL) SULFOSUCCINATE AND SODIUM BIS(2-ETHYLHEXYL) PHOSPHATE SYSTEMS

Static microstructures are qualitatively elucidated through some typical macroscopic properties for the sodium bis(2-ethylhexyl) sulfosuccinate (AOT)/water/n-hexane/sodium chloride and the sodium bis(2-ethylhexyl) phosphate (SDEHP)/water/n-hexane/sodium chloride systems in the concentrated region of the surfactants. The AOT microemulsions are composed of spherical aggregates immersed in the organic solvent even if the volume fraction of the aggregates is high. In SDEHP microemulsions, which are composed of cylindrical aggregates in the dilute region, the cylindrical aggregates assemble into a branched structure as the volume fraction of the aggregates Phi(BS) increases. When Phi(BS) greater than or equal to 0.2, the assemblies are packed densely and overlap mutually, and consequently, a transient network structure expanded all over the SDEHP microemulsion is formed. The geometrical form of the individual aggregates in the dilute region strongly influences the microstructure of the microemulsion in the concentrated region.