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

Static microstructures are qualitatively elucidated through some typic al macroscopic properties for the sodium bis(2-ethylhexyl) sulfosuccin ate (AOT)/water/n-hexane/sodium chloride and the sodium bis(2-ethylhex yl) phosphate (SDEHP)/water/n-hexane/sodium chloride systems in the co ncentrated region of the surfactants. The AOT microemulsions are compo sed of spherical aggregates immersed in the organic solvent even if th e 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 volu me fraction of the aggregates Phi(BS) increases. When Phi(BS) greater than or equal to 0.2, the assemblies are packed densely and overlap mu tually, and consequently, a transient network structure expanded all o ver the SDEHP microemulsion is formed. The geometrical form of the ind ividual aggregates in the dilute region strongly influences the micros tructure of the microemulsion in the concentrated region.