Pressure Dependence of the Melting and Self Diffusion in 2,2-dimethylpropane, 2,2-dimethylpropionitrile, and 2-methylpropanol-2

The melting pressure curves of 2,2-dimethylpropane, 2,2-dimethylpropionitrile and 2-methylpropanol- 2 and the pressure dependence of the hex ⇔ fee transition of 2,2-dimethylpropane have been determined in the pressure range between 0.1 and 200 MPa. The self diffusion coefficients D in the liquid state of the three compounds have been determined as function of pressure (pmax ≧ 120 MPa) from the melting pressure curve up to ca. 450 K. At high temperatures and high pressures the self diffusion coefficients of the three compounds become rather similar. The influence of the hydroxylgroup upon the diffusivity of (CH3)3COD is most clearly seen at the lowest temperatures. The isobars of C(CH3)4 and (CH3)3CCN are straight lines with identical slopes. For (CH3)3COD all isobars show a curvature. From the data in the Arrhenius representation activation volumes and activation energies are derived. For C (CH3)4 the density dependence of D can be described with the rough hard sphere model.