Critical Behavior of a Pseudobinary System for a Three-Component Microemulsion

Abstract

A three-component microemulsion system can be regarded as a pseudobinary mixture at certain conditions. The coexistence curves of (T, n), (T, φ), and (T, Ψ) (n and φ are refractive index and volume fraction, respectively; Ψ is defined as Ψ = φ/[φ + φc(1 − φ)/(1 − φc)]) for a ternary microemulsion (AOT−water−decane) at constant pressure and a constant ratio of water to AOT have been determined within about 10 K from the critical temperature by measurements of refractive index. The critical exponent β was deduced precisely from (T, n), (T, φ), and (T, Ψ) coexistence curves within 1.5 K above Tc. These values were 0.327, 0.324, and 0.325, respectively, and were consistent with the 3D Ising exponent. The volume fraction φ is a better choice of the concentration variable than Ψ used for construction of the order parameter to fit the Ising behavior.