Diffusion in high viscosity liquids

The diffusion coefficients D of n ‐hexane and of naphthalene in a series of hydrocarbon liquids with viscosities μ from 5 · 10 −4 to 5 kg m −1 sec −1 (0.5 to 5000 centipoise) have been measured at 25°C with a one Savart plate wavefront‐shearing interferometer. This apparatus allows direct determinations at effectively infinite dilution. The values obtained suggest that for a small solute diffusing in a large solvent\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {D\mu ^{2/3} } & = & {{\rm constant}} \\ \end{array} $$\end{document}a result consistent with earlier studies. The exponent of 2/3 may be rationalized on the basis of the Eyring rate theory.