STATIC AND DYNAMIC LIGHT-SCATTERING EXPERIMENTS WITH AN ISO-BUTOXYETHANOL WATER MIXTURE OF CRITICAL COMPOSITION/

Results of static and dynamic light scattering as well as of viscosity measurements are reported. They are carried out with an i-C4E1/water mixture of critical composition in the vicinity of its lower critical point (y(c) = 0.3180, mass fraction of i-C4E1; T-c = 26.350 degrees C) . This point is approached from temperatures T < T-c. The value of the critical amplitude xi(o) of the correlation length of local concentra tion fluctuations obtained from static light scattering experiments is combined with the known values of the critical amplitude sigma(o) of the liquid/liquid interfacial tension and the critical amplitude A(o,x ) the heat capacity at constant pressure per unit volume c(p) to calcu late the values of the universal amplitude ratios R(sigma,xi) and R(c( p),xi). The critical amplitudes are material-dependent quantities. The calculated values of x(sigma,xi) and R(c(p),xi) are consistent with t heir theoretical predictions. The ''hydrodynamic'' correlation length xi(hd) of concentration fluctuations is obtained by combining experime ntal viscosity and mutual diffusion coefficient data. The xi(hd) value s are in agreement with the corresponding values of xi obtained from s tatic light scattering experiments. The calculation of xi(hd) is based on an equation analogous to the Stokes-Einstein relation. The data of the diffusion coefficient are obtained from dynamic light scattering experiments. The material dependent critical amplitude Q(o) of the vis cosity is found to have a value typical of simple binary mixtures of l ow molar mass components. II is concluded that formation of aggregates of iC(4)E(1) molecules and/or i-C4E1 and water molecules in an i-C4E1 /water mixture of critical composition does not influence the critical properties of this system. The properties are in agreement with that predicted by the universality concept of critical phenomena.