Conductometric and Volumetric Studies on the Inonization, Hydration, Aggregation, and Coagulation of AOT in Dodecane

Abstract

Abstract For the sodium l,2-bis(2-ethylhexyloxycarbonyl)ethanesulfonate (AOT)/water/dodecane system, the conductivity (κ) of the solution as well as the partial molar volume of water was determined at 25 °C as a function of the water concentration (CW) at a given concentration of AOT (CA). The value of (κ) increased stepwise through 2 peaks before water-phase separation. Each step was assigned as follows. Upon the initial additions of water at all of the CA’s studied (CA < 0.2 mol kg−1 (dodecane)), κ remained zero, indicating the formation of unionized hydrate, AOT(H2O)2. The critical composition of the solution for reversed micelle formation was estimated to be CA = ca. 0.02 and CW = ca. 0.04 mol kg−1 (dodecane). After hydrate formation, micelles were formed in equilibrium with the hydrate, at which point κ increased abruptly to the 1st peak. Coagulation of the micelles occurred above another critical composition (CA = 0.120 and CW = 0.612 mol kg−1), at which point κ increased with a steep slope up to the 2nd peak. The partial molar volume of water in the same system also indicated the formation of AOT(H2O)2.