A study of isothermal diffusion in liquids

Abstract

The precise measurement of diffusion coefficients in liquids was undertaken to test the proposed relation of liquid properties. In Part I the intradiffusion coefficients of benzene-1-14C, n-hexane-1-14C, cyclohexane-1-14C, and N,N'-dimethylformamide-1-14C and viscosities were measured over the whole concentration range in the binary systems, benzene-cyclohexane, n-hexane-cyclohexane, benzene-n-hexane, and benzene-N,N'-dimethylformamide, and at four concentrations in the ternary system benzene-cyclohexane-n-hexane. The obtained values of intradiffusion coefficients and data reported for additional binary systems by other authors were used to test the equations which relate the viscosity and the diffusion coefficient. Agreement between measured and calculated viscosities was excellent for nonpolar liquid systems and some of nonpolar-polar liquid systems, but rather poor results were observed for most of the polar liquid systems. In Part II the mutual diffusion coefficients of I benzene and perdeuterobenzene were measured at very low solute concentrations in methanol, pentane, cyclopentane, hexane, cyclohexane, heptaine, methylcyclohexane, and hexadecane. The mutual diffusion coefficients of perdeuterobenzene were consistently lower than those of benzene, and strong solvent dependencies on the ratio of the diffusion coefficients of benzene and perdeuterobenzene were observed. A Graham's law accurately related the limiting intradiffusion coefficient of benzene-1- 14C and the limiting mutual diffusion coefficients of benzene and perdeuterobenzene in identical solvents. The results observed in this investigation supports the existence of an effect of mass on rate of diffusion. In Part III a simple one dimensional quasi-lattice model was proposed and the expressions for the intradiffusion processes were derived using the absolute rate theory. The derived equations were tested using the intradiffusion data. Agreement between calculated and measured concentration dependencies was good for most systems, but rather poor results were observed for the systems benzene-n-hexane, benzene-alcohol, and benzene-N,N'-dimethylformamide. The qualitative examination of concentration dependence of intradiffusion coefficients was also discussed.