Study of the Orientational Order and Dynamics in the Nematic and Smectic Phases of p′-Hexyloxybenzyliden-p-Fluoroaniline by Means of ²H-NMR

Abstract

Measurements of orientational order parameters and spectral densities of motion in the nematic, smectic A and smectic B phases of p′- hexyloxybenzyliden-p-fluoroaniline, fully deuterated in the chain and partially deuterated in the aniline ring, are reported. The deuterium spin-lattice (T_1Z) and quadrupolar (T_1Q) relaxation times have been measured at 46.04 MHz using a broadband multiple pulse Jeener-Broekaert sequence. The orientational order of the C-D bonds and the spectral densities determined suggest that, on entering the highly ordered smectic phases, the internal motions of the first two methylene groups in the chain slow down sensibly. These effects are discussed within the framework of the models used to describe molecular and internal dynamics in mesomorphic phases.