Water-AOT-alkylbenzene microemulsions: influence of alkyl chain length on structure and percolation behavior.

Abstract We study the percolation behavior of the water-in-oil (w/o) droplet phase of AOT (sodium bis[2-ethylhexyl] sulfosuccinate)-based microemulsions with different alkylbenzenes (toluene, ethylbenzene, butylbenzene or octylbenzene) as oil phase. We use microemulsions of varying composition with molar water to surfactant ratios 0 ⩽  W  ⩽  50 and droplet (water plus surfactant) volume fractions 10% ⩽  ϕ  ⩽ 50%. Using dielectric spectroscopy, a percolation transition is observed in w/o microemulsions with butylbenzene or octylbenzene. With increasing molecular weight of the alkylbenzene, the percolation temperature T P decreases. The structure of the microemulsions is determined by small angle X-ray scattering (SAXS). With increasing molar weight of the alkylbenzene, the stability range of the L 2 droplet phase extends to higher W . The larger amount of solubilizable water can be related to variable oil penetration of the AOT monolayer, which affects the spontaneous curvature of the surfactant shell.