Static and dynamic light scattering experiments with an iso-butoxyethanol/water mixture of critical composition

Abstract

Abstract Results of static and dynamic light scattering as well as of viscosity measurements are reported. They are carried out with an i-C 4 E 1 /water mixture of critical composition in the vicinity of its lower critical point (y c = 0.3180, mass fraction of i-C 4 En 1 ; Tc = 26.450 °C). This point is approached from temperatures T c . The value of the critical amplitude ξ o of the correlation length of local concentration fluctuations obtained from static light scattering experiments is combined with the known values of the critical amplitude σ o of the liquid/liquid interfacial tension and the critical amplitude A o,v the heat capacity at constant pressure per unit volume c p to calculate the values of the universal amplitude ratios R ( σ , ξ ) and R (c p , ξ ). The critical amplitudes are material-dependent quantities. The calculated values of R ( σ , ξ ) and R (c p , ξ ) are consistent with their theoretical predictions. The “hydrodynamic” correlation length ξ hd of concentration fluctuations is obtained by combining experimental viscosity and mutual diffusion coefficient data. The ξ hd values are in agreement with the corresponding values of ξ obtained from static light scattering experiments. The calculation of ξ 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 viscosity is found to have a value typical of simple binary mixtures of low molar mass components. It is concluded that formation of aggregates of i-C 4 E 1 molecules and/or i-C 4 E 1 and water molecules in an i-C 4 E 1 /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.