Critical Behavior of {Water + AOT + Decane} Microemulsion with Small Molar Ratio of Water to AOT

Abstract

The coexistence curves of (T,n), (T,φ) and (T,ψ) (n,φ,ψ are the refractive index, the volume fraction, and the effective volume fraction, respectively) for a ternary microemulsion system of {water + sodium di(2-ethylhexyl) sulfosuccinate (AOT) + n-decane} with the molar ratio 25.1 of water to AOT have been determined at constant pressure within about 7 K from the critical temperature Tc by measurements of refractive index. The critical exponent β has been deduced from the (T,n), (T,φ) and (T,ψ) coexistence curves within 1 K above Tc. They were 0.323, 0.327, and 0.329, respectively, and were consistent with the 3D-Ising value. Furthermore, the experimental results have been analyzed to obtain critical amplitudes B and the Wegner-correction terms B1, to examine the diameters of the coexistence curves and to discuss the goodness of density variables for constructing order parameters.