Coexistence Curves of a Critical Microemulsion of AOT–water–octane

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The coexistence curves of (T,n), (T, φ) and (T, Ψ) (nand φ are refractive index and volume fraction, respectively; Ψ is defined as Ψ = φ/[φ + φc(1 − φ)/(1 − φc)]) for a ternary microemulsion [φ(AOT–water) − (1 − φ)octane] at constant pressure and a constant MOLAR ratio (40.8) of water to AOT have been determined within about 10 K from the critical temperatureTcby measurements of refractive index. This system can be regarded as a pseudobinary mixture. The critical exponent β has been deduced from (T,n), (T, φ), and (T, Ψ) coexistence curves within 1 K aboveTc. They were 0.320, 0.325, and 0.320, respectively, and were consistent with the 3D Ising value. The experimental results in a temperature range of (T − Tc) < 5 K also have been analyzed to obtain critical amplitudes and the Wegner-correction terms, to examine the diameters of the coexistence curves, and to discuss the goodness of density variables for constricting order parameters.