High-Pressure Phase Studies of Some 4,4′-Disubstituted Phenylcyclohexanes (PCHs) and Bicyclohexanes (CCHs) by DTA

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Abstract
T-p phase diagrams of the mesogenic compounds trans-4-n-dodecyl(4-cyanophenyl)cyclohexane (12PCH), trans-4-n-propyl(4-n-alkoxyphenyl)cyclohexanes (alkoxy = ethoxy (302PCH) and butoxy (304PCH)), and trans, trans-4-n-propyl(4-cyanocyclohexyl)cyclohexane (3CCH) are presented. The investigationswere performed with new high-pressure computer-assisted DTA equipment in the temperature range300 to 500 K up to a maximum pressure of 7 kbar. Several high-pressure effects typical for liquid crystalscould be observed, e.g., pressure-induced phases (nematic and smectic), the occurrence of triple points, complex solid state polymorphism, changes in the nature of phase transitions from monotropic toenantiotropic etc. The T-p phase diagrams are discussed with regard to the influence of pressure onthe stability of the different phases and of systematic changes in molecular structure.