A TEST OF HYDRODYNAMICS IN BINARY SOLVENT SYSTEMS - ROTATIONAL DIFFUSION STUDIES OF OXAZINE-118

Rotational diffusion of the dye molecule oxazine 118 has been studied in DMSO/water and 1-propanol/water solvent mixtures as a function of temperature. The rotational relaxation time does not scale linearly with viscosity when the solvent composition is changed at a fixed temperature, as observed previously with other probe molecules. In a given solvent mixture the rotational relaxation time follows hydrodynamic predictions when the temperature is varied. The change in relaxation time with composition does not indicate a breakdown of hydrodynamic predictions but can be interpreted as arising from a change in the hydrodynamic boundary condition. Models for the changing boundary condition are evaluated.