DYNAMIC CRITICAL PHENOMENA IN WATER-BUTOXYETHANOL MIXTURES STUDIED BYVISCOSITY AND LIGHT-SCATTERING MEASUREMENTS

We have used shear viscosity and dynamic light scattering to study the critical behavior in a water-butoxyethanol (C4E1) mixture as a functi on of temperature. The data of viscosity and of the relaxation rate ar e analyzed in terms of the mode-coupling theory, taking into account b ackground effects on the transport coefficient. From experimental data we measure both the short-range correlation length xi0 and the Debye cutoff length q(D)-1, whose values confirm the micellarlike structural picture proposed for such a water-alcohol mixture. Furthermore, we fi nd evidence for a crossover from critical to single-particle behavior in the light-scattering data. The crossover temperature T(x) is found to be such that q(D)xi(T(x)) congruent-to 1. For both the measured qua ntities, i.e., viscosity and linewidth, the parameter q(D) plays the d eterminant role in the critical dynamics of the system.