Density dependence of self-diffusion in liquid pentanes and pentane mixtures

Self-diffusion coefficients of cyclopentane and 2-methylbutane (isopentane) were measured in the pure liquids and in an equimolar mixture of the compounds by the Fourier transform NMR spin-echo technique. Measurements were made for temperatures in the range 298-328 K and for pressures up to 200 MPa. Characteristic parameters (effective molecular diameters and attractive potential-well depths) for the two molecules were determined by fitting the data to the 'interacting hard-sphere' equations for self-diffusion in pure liquids. Equations for the self-diffusion of the individual components in the mixture are then proposed and tested. The results are also compared with those from molecular dynamics calculations.