Critical Behavior of {DMA plus AOT plus Octane} Nonaqueous Microemulsions with Various Molar Ratios of DMA to AOT

摘要

The coexistence curves of two nonaqueous microemulsions systems of {dimethylacetamide (DMA) + sodium di(2-ethyl-1-hexyl)sulphosuccinate (AOT) + n-octane}, with the molar ratios omega=(3.06 and 3.86) of DMA to AOT, were determined by precisely measuring the refractive index at constant pressure at temperatures within about 7 K of the critical temperature T (c). The critical exponents beta and critical amplitudes B have been deduced from the coexistence curves. It was found that the values of beta for both systems are inconsistent with the expected 3D-Ising value but approach the Fisher-normalization value of 0.365 over a rather wide temperature range. By increasing the molar ratio omega, the critical temperature T (c) increases, but the critical (volume fraction) composition phi (c) decreases, which is different from the trends observed for aqueous microemulsions.