INHOMOGENEITY OF VISCOUS AQUEOUS-SOLUTIONS

Brownian principles for homogeneous media fail to explain the effect of viscous cosolvents on reaction rates. We examined the possibility that solvent viscosity in the microenvironment of a probe eta* (microviscosity) differs from the bulk viscosity eta (macroviscosity). eta* was derived from the diffusion constant D of water tracers, measured in the presence of viscous cosolvents. We found that (a) eta*proportional to eta(alpha), where 0 less than or equal to alpha less than or equal to 1, and (b) the temperature dependence of D is insensitive to the presence of these cosolvents. We propose that viscous aqueous solutions have an inhomogeneous microstructure with waterlike domains.