MEASUREMENT OF DEUTERON SPIN RELAXATION TIMES IN LIQUID CRYSTALS by a BROADBAND EXCITATION SEQUENCE

Liquid crystals are composed of flexible organic molecules and capable of forming different ordered structures in their mesophases. Nuclear spin relaxation [1], [2] is a powerful technique that provides useful information on the molecular dynamics of liquid crystals. There are collective director fluctuations, molecular reorientation and internal rotations in flexible end chains. Recently internal dynamics of mesogenic molecules has attracted much attention. Both theoretical [3], [4] and experimental [5], [6] studies have been carried out. Experimentally carbon-13 and deuteron may be used to probe internal dynamics of flexible mesogens. In aligned samples of deuterated liquid crystals, deuterium NMR spectroscopy yields well-resolved spectral lines having different quadrupolar splittings for various atomic sites. These quadrupolar splittings result from incomplete averaging by anisotropic reorientation of molecules in the mesophases. For a single deuteron spin (1=1), there are five independent spin relaxation times [7]. These are two spin-lattice relaxation times and three independent spin-spin relaxation times. Since the deuterium Zeeman (T\z) and quadrupolar (T\Q) spin-lattice relaxation times are given by [7],