Electric field N.M.R. of pretransitional effects in liquid crystals A solute study

Abstract

Pretransitional effects in the isotropic phase of liquid crystals are manifest in the N.M.R. spectra of solutes recorded in the presence of an applied electric field. The temperature dependence of the quadrupolar splittings of p-xylene-d ₁₀ in the isotropic phase of the nematogen 4-n-pentyl-4'-cyanobiphenyl is investigated, and proves to be as expected from the Landau-de Gennes theory for pretransitional effects. The influence of temperature in the biphasic region of the phase diagram is very striking: the orientational ordering of the solute is temperature independent. The applied electric field not only determines the ordering of the solute, but also has a clear effect on the transition temperature. Electric field N.M.R. of solutes to study pretransitional effects is an alternative to the investigation of the nematogen itself.