Dielectric Studies on Liquid Crystals under High Pressure: V. Static Permittivity and Low Frequency Relaxation Process in 4‐n‐Heptyl‐4'‐Cyanobiphenyl (7CB)

Abstract

Abstract Dielectric studies have been performed on 4‐n‐heptyl‐4'‐cyanobiphenyl, 7CB, between 305 and 341 K and at elevated pressures up to 150MPa. From measurements of the dielectric relaxation (up to 13 MHz) we calculate the activation enthalpy (decreasing with increasing pressure) and the activation volume (decreasing with increasing temperature) in the nematic state. The low‐frequency process connected with molecular rotations about the short molecular axis was analysed in terms of the Martin‐Meier‐Saupe theory, yielding q ≈︁ 5 kJ/mol for the nematic potential. The dielectric behaviour is similar to previous results for 5CB and 6CB.