Study of the Molecular Dynamics from Deuterium Zeeman and Quadrupolar NMR Relaxation of 4,4´-di-n-Heptylazoxybenzene in the Nematic and Smectic A Phases

Abstract

Abstract The deuterium spin-lattice (T1Z) and quadrupolar (R1Q) relaxation times of the liquid crystal 4,4´-Heptyl-azoxybenzene (HAB), deuterated on the aromatic rings and the first methylene group of the chains, have been measured by means of the Jeener-Broekaert pulse sequence at two different frequencies (10 and 46.04 M Hz) and throughout the nematic and the smectic A phase. By applying suitable models, we have determined rotational and reorientational diffusion coefficients and evalu­ated the contribution of the different motions (internal, molecular and collective) to the relaxation. In particular we have found a non negligible contribution from order director fluctuations. A comparison between the T1Z and T1Q measurements performed by means of Jeener-Broekaert and Wimperis pulse sequences is also shown.