REENTRANT BEHAVIOR IN PRESSURE-COMPOSITION PHASE-DIAGRAMS OF LIQUID-CRYSTALS

For liquid crystalline pure compounds exhibiting re-entrant phenomena the chemical potential difference between two successive phases along the isotherm is supposed to have simple pressure dependence. For binar y mixtures of such compounds the thermodynamic approach called equal G ibbs energy analysis is applied to the study of their pressure-composi tion phase diagrams. Many types of isothermal phase diagrams which exh ibit re-entrant phase behaviour can be predicted by assuming perfect o r non-perfect nature (regular and non-zero excess molar volume) of the solutions. For the mesogenic system hexyloxy-octyloxy cyanobiphenyl, it is shown that the pressure-composition phase diagram is more succes sfully described with a regular solution hypothesis than with a perfec t hypothesis.