Solvation dynamics in binary mixtures

Abstract

The solvation dynamics of two binary mixtures are examined. Fluorescence upconversion spectroscopy is used to determine the solvation response function of the mixtures with ~ 250 femtosecond time resolution. The first mixture, dimethylsulfoxide(DMSO)-water, is a strongly interacting, hydrogen bonding mixture. It is shown that the DMSO-water mixtures display dramatic changes in their solvation response functions as compared to the pure solvents. These changes include both the inertial and diffusional response. The magnitude of the inertial response is seen to diminish when the solvents are mixed. The diffusional response maximizes at 33% DMSO, which corresponds to a 2DMSO-1 water complex. Quasi-elastic neutron scattering is also included for water in the above mixtures. The second mixture is benzene-acetonitrile. This mixture is non-associating and involves both a nonpolar and strongly polar solvent The solvation response function is seen to be sensitive to the mixing of the pure solvents, affecting both the inertial and diffusive portions of the solvation response function. The addition of acetonitrile to benzene is seen to increase the magnitude of the inertial response of the mixtures. At high benzene concentrations the diffusive portion shows a slow component that is attributed to translational diffusion of the acetonitrile.