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

Abstract

DTA measurements of 4-/i-butyl-thiocyanobiphenyl (4TCB) and/?-cyano-/?'-pentylphenyl-cyclohexane (5HCP) have been performed in the temperature range 220 K-390 K and pressures up to 400 MPa. For 4TCP a transition from a crystalline to a liquid crystal phase (probably smectic E) could be detected at higher pressures > 90 MPa. The pressure dependence of the transition temperature has been established. At pressures lower than 88.7 MPa no transition of SmE into a crystal or into a glass has been found. For 5HCP only the melting curve was observed, in contrast to 5PCH, which displays a liquid crystalline nematic phase.

Molecular Dynamics and Residual Entropy in the Soft Crystal, SmE Phase, of 4-Butyl-4‘-isothiocyano-1,1‘-biphenyl

“…Above this phase transition, the heat capacity coincides with those of the SmE phase. Since the location of the thermal anomaly is reasonably close to the extrapolated one from the high-pressure DTA results, it is concluded that the sample after the two-step anneal is in the ordered crystalline phase.

1 Measured heat capacities of the quenched (open circle) and annealed (plus-sign) SmE phase, and of the ordered crystalline phase (filled circle) of 4TCB.

…”

“…No ordered crystalline phase has been reported under ambient pressure. The ordered crystalline phase was formed only under high pressure above 88.7 MPa . This peculiar phase behavior of 4TCB opens the possibility to study the properties of the SmE phase in detail over a wide temperature range.…”

Reassessment of structure of smectic phases: Nano-segregation in smectic E phase in 4-n-alkyl-4′-isothiocyanato-1,1′-biphenyls

“…1, because a binary system between n-nonane and 4-n-alkyl-4 -isothiocyanato-1,1biphenyl (abbreviated as nTCB with n being the number of carbon atoms in the alkyl chain, shown in Fig. 2 for n = 4), on which the largest number of studies has been reported as a representative of SmE mesogens, 3,7,8,[15][16][17][18][19][20][21][22][23][24][25][26][27][28] exhibits a swollen SmE phase in a continuous range of composition. 29 Only the c, the cell constant parallel to the molecular long axis in average, exhibits a notable increase in swelling while retaining the three-dimensional periodicity.…”