A THERMODYNAMIC ANALYSIS OF REENTRANT CYANOESTER LIQUID-CRYSTAL SYSTEMS

The phase diagrams of 4-n-alkoxyphenyl 4'-cyanobenzoate nOPCB, n = 6, 8, and 12, and 4-cyanophenyl 4'-n-octyloxybenzoate CP8OB binary system s studied by Goodbye et al. (Goodby, J. W.; Leslie, T. M.; Cladis, P. E.; Finn, P. L. Liquid Crystals 6 Ordered Fluids; Griffin, A. C., John son, J. F., Eds.; Plenum: New York, 1984; Vol. 4 pp 89-110, 203-231) a re analyzed thermodynamically. For the systems 6OPCB/8OPCB, 6OPCB/12OP CB, CP8OB/12OPCB, and CP8OB/8OPCB, the change in Gibbs excess energy f or the reentrant nematic-smectic A transition extracted as a function of composition and temperature is highly temperature-dependent. For th e same systems, the change in excess energy for the nematic-isotropic transitions is fit with a third-order Redlich-Kister expression. The c ompound 12OPCB is further analyzed to obtain transition enthalpies and predict transition temperatures for all relevant stable and metastabl e phase transitions. From these results, a semiquantitative chemical p otential-temperature plot for 12OPCB was generated. A calculated phase diagram was prepared for the 6OPCB/12OPCB system.