The influence of high pressure on the discontinuity of the isotropic-nematic and the isotropic-smectic A phase transitions studied by the low-frequency nonlinear dielectric effect measurements

Results are presented for isothermal, pressure studies of the low frequency nonlinear dielectric effect in the isotropic phase of 8CB (isotropic - nem atic (I-N) transition) and 12CB (isotropic - smectic(I-SmA transition), Thi s made possible to determined the pressure dependence of the nematic and sm ectic clearing temperatures as well as the extrapolated temperatures of a h ypothetical continuous phase transition up to P = 200 MPa. Ln the case of t he I-N transition the discontinuity of the transition (Delta T) increases s ystematically with pressure while for the I-SmA transition Delta T decrease s with rising pressure.