STATIC LIGHT-SCATTERING EXPERIMENTS WITH NONIONIC SURFACTANT WATER MIXTURES OF CRITICAL COMPOSITION

Results of static light scattering experiments with C6E3/water and C8E4/water mixtures of critical composition carried out near the lower critical point of these systems are reported. If the critical temperature of the mixtures is constant in time (months) the critical exponent nu of the correlation length of local concentration fluctuations and that of the generalized susceptibility gamma have values consistent with the values predicted theoretically for binary liquid mixtures (Landau-Wilson-Ginzburg model: nu = 0.63; gamma = 1.24). The system specific critical amplitude xi0 of the correlation length xi has the values xi0 (C6E3/water) = 0.36 nm and xi0 (C8E4/water) = 0.54 nm. The evaluation of experiments with samples with time dependent critical temperatures introduces systematic errors. They lead to values of nu and gamma smaller than the theoretically expected values. This observation could be one of the reasons for reports in the literature of non-universal values of the critical exponents nu and gamma in non-ionic surfactant/water systems.