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 are refractive index and volume fraction, respectively; ψ is defined as ψ=φ/[φ+φc(1-φ)/(1-φc)]) for a ternary microemulsion (AOT-waterdecane) 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 is a better choice of the concentration variable than ψ used for construction of the order parameter to fit the Ising behavior.

The enzymatic activities of wheat germ lipase (WGL) (EC.3.1.1.3; triacylglycerol hydrolase) in water-in-oil (w/o) microemulsions of sodium bis-(2-ethylhexyl) sulfosuccinate (AOT)/cyclohexane/water have been investigated by using triolein as the substrate through measurements of absorbency of the product of hydrolysis at the wavelength of 707 nm in the course of reactions. Maximum enzyme activity was obtained at ω0 (molar ratio of water to surfactant)=9, pH=7.4 and T=40℃. The activation energy of the reaction was calculated from the Arrhenius plot. It was found that the hydrolysis reaction obeyed Michaelis-Menten kinetics in the investigated concentration range (0.01-0.15 mol/l) of the substrate, and the apparent Michaelis constant Km,a and the apparent maximal reaction rate Vm were determined. The stability of wheat germ lipase in w/o microemulsions was also examined and discussed.