EFFECT OF MOLECULAR-SIZE AND FREE-VOLUME ON DIFFUSION IN LIQUIDS

The concept of free volume is used to describe self-diffusion in liquids. It is found that for different organic liquids (including chloroform, carbon tetrachloride, p-xylene, o-xylene, toluene, n-hexane, n-heptane, acetone etc.), straight lines are obtained by plotting ln (D(ii)/RT) against (1/f(i)) which yield a common intercept. It is also found that the rate of diffusion is directly related to the molecular volume and shape of the diffusing molecule. These findings allow the prediction of the self-diffusion coefficient of a binary liquid mixture. The predicted results for 12 liquid pairs and for the diffusion of different molecules in polyethylene are given. These results match experimental data reasonably well.