Kerr effect and orientation relaxation of pretransitional domains and individual molecules in positive dielectric liquid crystals

摘要

Measurements are reported on the static and the dynamic pretransitional behavior of the electrical birefringence (Kerr effect) of strongly positive dielectric anisotropic liquid crystals. The exceptionally large Kerr constants measured exceed that of nitrobenzene by more than a factor of 200 near the nematic to isotropic transition temperature. The orientation relaxation of the pretransitional domains of highly correlated molecules was investigated using achyphen;driven Kerr cells. Two relaxation processes with relaxation times in the range 10minus;7ndash;10minus;8sec were found to determine the dynamics of the domain relaxation. The respective processes are shown to be due to an induced and a permanent dipolar relaxation of the domains. The orientation relaxation times of the individual molecules were determined in the nematic state as well as in the pretransitional domains in the isotropic phase by measuring the conductivity relaxation.