PVT Measurements on 4-n-Pentyl-4´-Cyano-Biphenyl (5CB) and trans-4-(4´-Octyl-Cyclohexyl)-Benzonitrile (8PCH) up to 300 MPa

Abstract

Specific volumes are presented for 4-n-pentyl-4'-cyanobiphenyl (5CB) and trans-4-(4'-octyl-cyclohexyl)-benzonitrile (8PCH) for temperatures between 300 and 370 K up to 300 MPa. The p,V m ,T data were determined for the liquid crystalline and isotropic phases, and partly also for the solid phase adjacent to the melting curve. Stable and metastable crystal phases can be distinguished. The density and melting temperature of the metastable form are lower than for the stable one. Volume and enthalpy changes accompanying the phase transitions are reported as well. The p,V m ,T data allow to calculate the entropy change for a hypothetical transition at constant volume. The molar volumes along the nematic-isotropic phase transition T NI (p) allow to determine the molecular field parameter y = S In T NI /0 In F N ,.

PVT Measurements on 4′-n-Octyl-Biphenyl-4-Carbonitrile (8CB) up to 300 MPa

“…Brought to you by | MIT Libraries Authenticated Download Date | 5/10/18 6:49 AM Bauman et al [17] As in previous papers we can split the entropy change, AS tr , at a first-order phase transition into a constant-volume (or configurational) part, and a dilatational part [1,2]. The latter part is evaluated using ourp, V m , Tdata: AS v =(^V) T AV tI =(dpW) v AV tI .…”

“…The high-pressure dilatometric cell has been described previously [1,5]. In general the volume changes are recorded after equilibration of the temperature on decreasing the pressure.…”

“…In recent papers we reported p, V m , T data for 5CB [1], 6CB and 7CB [2], which are typical representatives of liquid crystals with rod-like molecules, exhibiting nematic phases at moderate temperatures. In this paper we extend the investigation to 8CB, which displays additionally a smectic A phase (S A ).…”

High-pressure DTA Studies of the Phase Behaviors of 4-n -butyl-thiocyanobiphenyl (4TCB) and 4-w-pentyl-4’-n-phenyl-cyanocyclohexane (5HCP)

“…Contrary to that for liquid crystalline materials possessing the nematic phase, the enthalpy changes are much larger for the solid -nematic transition than for the nematic -isotropic transition. For example for 5CB [3,9] A//(Cr-N)= 13.4 kJ/mol and A//(N-I) = 0.33 kJ/mol. It seems worth to note that the sum of the transition enthalpies from the solid to the isotropic phase is nearly the same in both 4TCB and 5CB.…”

Spatial Configuration and Thermodynamic Characteristics of Main‐Chain Liquid Crystals

“…The list contains dimer (also called twin compound), trimer, and polymer main-chain LCs; 4-n-alkyl-4 -cyanobiphenyls (nCBs) are included as representative examples of monomeric LCs [Béguim et al, 1984]. A comprehensive summary of the PVT properties is available for a series of nCBs (with n = 5 to 8) by Sandmann et al [1997] and Sandmann [1998]. It should be noted here that the series of dimers and trimers having cyanobiphenyl end groups has been studied independently by two groups, and is abbreviated differently in the literature; hence, both are cited in Figure 7.1.…”