Forced Rayleigh scattering is used to study the tracer diffusion of an azobenzene in binary combinations of polar solvents, including water. In the absence of water, the tracer diffusioncoefficient D in the mixture lies between the diffusion coefficients within the pure solvents, on a curve that is reasonably close to the prediction of free-volume theory. If water is present, on the other hand, the diffusion coefficient displays a minimum that is less than the smaller of the two pure-solvent values. We attempt to understand the different behavior in water by concentrating on the fairly hydrophobic nature of the solute, leading to a first solvent shell that is hydrophobicon the inside and hydrophilic on the outside. We also believe that clusters of amphiphiles explain the observation that, in aqueous combinations, D is nearly constant above a certain amphiphile mole fraction.
Document Object Identifier (DOI)
D. M. Frasch, D. R. Spiegel (2014). Experiments on Tracer Diffusion in Aqueous and Non-aqueous Solvent Combinations. Journal of Chemical Physics, v. 141, page 124507.
The Journal of Chemical Physics