Self-Diffusion and Viscosity of Some Liquids as a Function of Temperature Self-diffusion coefficients of 15 liquids have been measured as a function of temperature between their melting and boiling points. The systems investigated were the benzenes, CBH5X where X = H, F, C1, Br, and I, n-paraffins, CnHnfe where n = 7, 9, 10, 12, 14, 16, and 18, acetone, acetic acid and water. The pulsed nmr technique was employed for the diffusion measurements. In addition, the viscosities of the halogenated benzenes have been measured between 2OoC and their melting points.
The diffusion results obtained in this study have been found in excellent agreement with the best values available for benzene and water . The relation between the apparent H. ERTL and F. A. L. DULLIEN molecular diameter d (d = 2.24(7VD/RT)S) and the critical volume as suggested by Dullien (1972) has been extended to include the temperature dependence of d. It is also shown that the temperature dependence of d is similar for all liquids studied here with respect to the reduced temperature. The increase of d for T, < 0.46 shows the invalidity of the Stokes-Einstein relation for this temperature range (T, = T/Tc).
A normalized plot of d has been found very useful in checking the consistency of viscosity and self-diffusion data. The relations proposed in this work can be used to predict self-diffusion coefficients and viscosities over the normal liquid range.