Pressure Dependence of Self Diffusion in Some Neat Alkanes and Binary Mixtures

The self diffusion coefficients D have been measured for a series of linear and branched alkanes between the melting pressure curve and 450 K at pressures up to 200 MPa. The experiments were performed in a strengthened glass cell by application of the pulsed field gradient technique. — The p, T dependence of the data is described by the rough hard sphere model (Chandler) and by the interacting sphere model (Speedy). — The measurements have been extended to binary mixtures of a long chain alkane (tetradecane) and 4 to 12% w/w methane. The addition of relatively small amounts of the lower alkane enhances significantly the translational mobility and reduces the p. T dependence of the self diffusion coefficients of tetradecane.