title: Experiments on tracer diffusion in aqueous and non-aqueous solvent combinations.
abstract: 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 diffusion coefficient 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 hydrophobic on 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.
authors.affiliation: Department of Physics and Astronomy, Trinity University, San Antonio, Texas 78212, USA.
authors.forename: Duncan M
authors.initials: DM
authors.lastname: Frasch
authors.affiliation: Department of Physics and Astronomy, Trinity University, San Antonio, Texas 78212, USA.
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Spiegel
mesh_terms: D000096:Acetone / Q000737:chemistry; D001391:Azo Compounds / Q000737:chemistry*; D004058:Diffusion; D004121:Dimethyl Sulfoxide / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D015394:Molecular Structure; D012997:Solvents / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D001391:Azo Compounds; D012997:Solvents; D014867:Water; D000096:Acetone; C009850:azobenzene; D004121:Dimethyl Sulfoxide