STATIC LIGHT-SCATTERING EXPERIMENTS WITH AQUEOUS-SOLUTIONS OF THE NONIONIC TENSIDE C12E5 WITH CRITICAL AND NONCRITICAL COMPOSITION

Concentration fluctuations with long range correlations as well as non-critical background contributions determine the light scattering properties Of C12E5/H2O mixtures of critical composition near the lower critical point (critical mass fraction y(c) = 0.0123; critical temperature T(c) = 31.8-degrees-C). If the influence of the non-critical contributions is neglected, an evaluation of the light scattering data in terms of the power laws xi = xi(o) . epsilon(-nu) and chi(T) = chi(T.o) . epsilon(-gamma) (xi being the correlation length of local concentration fluctuations and chi(T) the generalized susceptibility; epsilon = (T(c) - T)/T(c) is the reduced temperature) leads to values of the critical exponents nu and gamma which are closer to the mean field values (nu = 0.5; gamma = 1) than to the values theoretically expected for binary liquid mixtures from the Landau-Ginzburg-Wilson model (nu = 0.63, gamma = 1.24). If the background contributions are taken into account empirically by adding temperature independent background terms xi(b) and chi(T,b) respectively' to the simple power laws, the analysis of the light scattering data leads to values of nu almost-equal-to 0.65 and gamma almost-equal-to 1.2, which are close to the values given by the Landau-Ginzburg-Wilson model. The background term xi(b) has a value of about xi(b) almost-equal-to 6 nm and the critical amplitude xi(o) a value of about xi(o) almost-equal-to 1.2 nm. This value for xi(o) is one order of magnitude larger than that found for simple binary liquid mixtures (O(xi(o)) almost-equal-to 0.1 nm). -In mixtures of non-critical composition (-0.79 < (y-y(c))/y(c) < 0.63) the scattered intensity shows an angular dependence which is also a function of temperature corresponding to correlation lengths 20 nm < xi < 206 nm for 0.5 K < (T(P)- T) < 7.0 K. They are assumed to reflect contributions of micelles which also contribute to the scattering of the mixture of critical composition away from the critical temperature.