Turbidity measurements of critical solutions of n-alkanes in nitrobenzene

Abstract

A series of turbidity measurements have been made for the critical solutions of n-decane, n-dodecane, and n-tetradecane in nitrobenzene at various wavelengths and temperatures. The turbidity data have been fitted to the Ornstein–Zernike equation to obtain the correlation lengths ζ and the osmotic compressibility χ as functions of reduced temperature t [t = (T-T_c)/T_c], and the corresponding critical exponents ν and γ. The values of ν and γ are consistent with the theoretical predictions of 1.241 and 0.63 within experimental uncertainties. The experimental results have also been analyzed to determine the corresponding critical amplitudes ζ₀ and χ₀ when γ and ν are fixed at their theoretical values. Combing our earlier experimental results for systems of n-octane and n-hexadecane in nitrobenzene, we have determined M exponents f and g, which characterize the power-law dependence of ζ₀ and χ₀ on molar mass of n-alkane. The values of f and g are, respectively, 0.21 ± 0.04 and −0.12 ± 0.09, and are in good agreement with that observed from polymer solutions, which indicates that they are universal for chain molecule solutions of both small molecules and polymers. These universal values support the Landau–Ginsburg–Wilson type model we proposed recently.