Pretransitional behaviour of liquid crystals in electric fields detected by N.M.R.

Abstract

Pretransitional phenomena in the isotropic phase of a liquid crystal have been observed by N.M.R. spectroscopy in the presence of an electric field. The temperature dependence of the proton-proton dipolar couplings is in agreement with the phenomenological Landau-de Gennes theory for the isotropic-to-nematic phase transition. The calculated alignment is nearly two orders of magnitude larger than normally obtained for non-liquid-crystalline polar compounds in electric fields. An increasing flexibility of the alkyl chain in the liquid crystal, from the α-methylene to the terminal methyl group, is clear from the spectra.