Formulation of Stokes’ Radii in DMF, DMSO and Propylene Carbonate with Solvent Structure Cavity Size as Parameter

Conductance of univalent ions in DMSO (dimethyl sulfoxide), DMF (dimethylformamide) and PC (propylene carbonate) was determined by use of tetrabutylammonium-tetrabutylborate as standard electrolyte of equal cationic and anionic conductance. Empirical formulation of Stokes’ radius was attempted on the assumption of a structure-cavity affecting the ionic transport in a medium of aprotic and polar solvent as well as water. By application of classical fluid dynamics Stokes’ radius rs is given in terms of −(2⁄3)rc+(1⁄σs) (rc–ro)2, where rc is crystal ionic radius, ro and σs are parameters characteristic of the cavity and molecular sizes, respectively, with respect the solvent.