Pretransitional phenomena in liquid crystals studied via electric field induced deuterium quadrupolar splittings

Abstract

The application of intense d.c. electric fields to a sample of 4-n-pentyl-α-d₂-4′-cyanobiphenyl (5CB-d₂) is shown to produce a large splitting, Δ[vtilde], in the deuterium N.M.R. resonance. The values of Δ[vtilde] are shown to depend on the square of the applied electric field strength, and to diverge as a hypothetical second order transition to a nematic phase as a temperature T* is approached. The divergence follows the (T - T*)^-1 dependence predicted by both molecular field and Landau-de Gennes theories, with T _NI - T* = 1·10 ± 0·05 K. The linewidths also diverge as (T - T*)^-1 while the spin lattice relaxation rate shows no divergence. This is similar to the behaviour reported for deuterons in 4-methoxybenzylidene-4′-n-butylaniline but not for nitrogen-14 in 4,4′-dimethoxyazoxybenzene.