HIGH-PRESSURE DIFFERENTIAL THERMAL-ANALYSIS OF NEMATIC COMPOUNDS WITHDIFFERENT MOLECULAR SHAPES

By means of high pressure differential thermal analysis we measured th e pressure/temperature phase diagrams of several nematic compounds wit h different molecular structures. Using pressures up to about 500 MPa we found strongly nonlinear clearing curves. This behaviour is interpr eted as changes from 'weak' intermolecular potentials to 'hard' potent ials, or using thermodynamic arguments, strong pressure dependence of the volume discontinuity at the clearing transitions.