MODIFICATION OF SOLVENT ROTATIONAL-DYNAMICS BY THE ADDITION OF SMALL MOLECULES OR POLYMERS

We address the general problem of how the addition of a solute to a solvent affects the rotational dynamics of the solvent. New experimental results for two types of systems are presented. In the first set of experiments, the solute is a macromolecule (polystyrene, polyisoprene, or polybutadiene) and the solvent is toluene. In the second set of experiments, a mixture of two small molecules (1-methylcyclohexene and 1-chloronaphthalene) is studied. For this mixture the dynamics of both components are monitored across the entire composition regime. Consistent with our previous work, we find that the effect of the solute on the solvent dynamics is related to the difference in time scales between solvent and solute reorientational motion. A simple hydrodynamic model which explains this result is presented. C-13 and H-2 NMR relaxation measurements were used to determine rotation times.