Solute–solvent interaction effects on tracer diffusion coefficients

Abstract

Tracer diffusion coefficients (D) for a variety of dipolar and non-dipolar solutes have been measured at normal atmospheric pressure in solutions of acetonitrile, toluene, n-hexane and water at 298.15 K, and in octamethylcyclotetrasiloxane (OMCTS) at 323.15 K. The diffusion coefficients are linearly correlated with the reciprocals of the equivalent hard-sphere diameters (σ) of the solutes for all the solvents except OMCTS, for which ln D is a linear function of 1/σ.In acetonitrile the dipolar solutes are differentiated from the non-dipolar solutes, whereas in toluene that distinction disappears. In n-hexane the solutes again exhibit two classes of behaviour, but in this case the classes do not correspond to dipolar and non-dipolar solutes. Water as solvent appears to distinguish solutes which can undergo hydrogen-bonding interactions with it from those which cannot. The behaviour of solutes in OMCTS is similar, except that solutes with hydroxylic protons form a separate class from the other solutes.