Interfacial rigidity and topology of reverse microemulsions: Influence of alcohol molecules

Abstract

Using dielectric relaxation spectroscopy and small-angle neutron scattering techniques, we present a quantitative analysis of the influence of short-chain (ethanol) and long-chain (octanol) alcohol molecules on the elastic bending constants of AOT [sodium-1,4-bis(2-ethylhexoxy)-1,4-dioxobutane-2-sulfonate]-stabilized reverse microemulsions. A significant increase in the elastic bending rigidity, κ, of the AOT surfactant layer (30.7%) is observed with the inclusion of octanol, whereas a decrease in κ amounting to 11.2% is obtained in the presence of ethanol. The experimentally elusive saddle-splay modulus, κ¯, of alcohol-loaded microemulsions is determined using a novel approach. Notably, the ratio κ¯/κ lies in the range −2<κ¯/κ<0, which is acceptable for spherical microemulsion droplets. Further, the presence of ethanol molecules causes a decrease in the percolation threshold temperature owing to an increase in the fluidity of the surfactant monolayer at the oil–water interface. On the other hand, the addition of octanol molecules shifts the percolation threshold to higher temperatures implying a further reinforcement of the surfactant film.