VISCOSITY AND DIFFUSIVITY OF A BINARY-LIQUID MIXTURE OF CRITICAL COMPOSITION - STUDY OF THE SYSTEM 2-BUTOXYETHANOL WATER

Results of measurements of the temperature dependence of the shear vis cosity and the mutual diffusion coefficient of a 2-butoxyethanol/water mixture of critical composition are reported. The shear viscosities a re measured with a capillary viscometer, and the diffusion coefficient s by dynamic light scattering. The viscosity data are used to determin e the regular (background) and the singular (critical) part of the vis cosity [eta(b); eta = eta(b)(Q0xi)zeta] and to analyze the crossover r egime. Q0 has a value of Q0 = (1.54 +/- 0.60) x 10(6) cm-1, which is s mall for a binary mixture of components of small molar mass. The visco sity is dominated by singular contributions in a narrow temperature ra nge (T(c) - T) less-than-or-equal-to 1.2 K. The singular contributions can be neglected for temperatures (T(c) - T) greater-than-or-equal-to 11 K. The function eta = eta(b) exp{z(eta)H}, given in the literature , represents the viscosity data in the temperature range 3 mK less-tha n-or-equal-to (T(c) - T) less-than-or-equal-to 25 K using the asymptot ic form of the function H for (q(d)/q(c)) --> 0 (q(d), q(c), parameter of the theory). This limit corresponds to the case in which the backg round diffusion coefficient D(b) can be neglected. The reduced diffusi on coefficient D calculated from the light-scattering data as a funct ion of the scaling variable x ( = qxi) is represented by the approxima tion of the dynamic scaling function proposed in the literature.