DIELECTRIC STUDIES ON LIQUID-CRYSTALS UNDER HIGH-PRESSURE .5. STATIC PERMITTIVITY AND LOW-FREQUENCY RELAXATION PROCESS IN 4-N-HEPTYL-4'-CYANOBIPHENYL (7CB)
T. Bruckert et al., DIELECTRIC STUDIES ON LIQUID-CRYSTALS UNDER HIGH-PRESSURE .5. STATIC PERMITTIVITY AND LOW-FREQUENCY RELAXATION PROCESS IN 4-N-HEPTYL-4'-CYANOBIPHENYL (7CB), Berichte der Bunsengesellschaft fur Physikalische Chemie, 97(10), 1993, pp. 1209-1213
Citations number
29
Categorie Soggetti
Chemistry Physical
Journal title
Berichte der Bunsengesellschaft fur Physikalische Chemie
Dielectric studies have been performed on 4-n-heptyl-4'-cyanobiphenyl,
7CB, between 305 and 341 K and at elevated pressures up to 150 MPa. F
rom measurements of the dielectric relaxation (up to 13 MHz) we calcul
ate the activation enthalpy (decreasing with increasing pressure) and
the activation volume (decreasing with increasing temperature) in the
nematic state. The low-frequency process connectcd with molecular rota
tions about the short molecular axis was analysed in terms of the Mart
in-Meier-Saupe theory, yielding q almost-equal-to 5 kJ/mol for the nem
atic potential. The dielectric behaviour is similar to previous result
s for 5CB and 6CB.