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

• DOI: 10.1007/s10953-009-9468-2
• Publication Date: 2009-11-19T17:28:37Z
• Authors: Hong-Lan Cai; Xue-Qin An; Hui-Hong Lü; Qing-An Qiao; Wei-Guo Shen
• Keywords: Microemulsion; Molar ratio

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 ω=(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 β and critical amplitudes B have been deduced from the coexistence curves. It was found that the values of β 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 ω, the critical temperature T c increases, but the critical (volume fraction) composition φ c decreases, which is different from the trends observed for aqueous microemulsions.