DIELECTRIC STUDIES ON LIQUID-CRYSTALS UNDER HIGH-PRESSURE .6. LOW-FREQUENCY RELAXATION PROCESS IN THE NEMATIC AND SMECTIC A PHASE OF 4-N-OCTYL-4'-CYANOBIPHENYL (8CB)
S. Urban et al., DIELECTRIC STUDIES ON LIQUID-CRYSTALS UNDER HIGH-PRESSURE .6. LOW-FREQUENCY RELAXATION PROCESS IN THE NEMATIC AND SMECTIC A PHASE OF 4-N-OCTYL-4'-CYANOBIPHENYL (8CB), Zeitschrift fur Naturforschung. A, A journal of physical sciences, 49(4-5), 1994, pp. 552-558
Dielectric relaxation studies of 4-n-octyl-4'-cyanobiphenyl (8CB) were
performed in the pressure range 0.1-120 MPa, the frequency range 1 kH
z-13 MHz and the temperature range 295-331 K. The dielectric behaviour
of 8CB in the nematic phase is similar to that of 5CB, 6CB and 7CB. I
n particular, the activation enthalpy decreases with increasing pressu
re and the activation volume decreases with increasing temperature in
the nematic phase. In the smectic A phase of 8CB both these parameters
are markedly lower and show opposite pressure and temperature depende
ncies. We tentatively interpret these effects as a result of breaking
of the dipole-dipole correlations which manifests itself differently i
n these liquid crystalline phases.