Phenyl ring dynamics in a liquid crystal polymer through H-2 NMR spectroscopy

The dynamics of a side chain liquid crystal copolymer at two different comp ositions has been investigated in its smectic A and C phases. J(1) (omega ( 0)) and J(2)(2 omega (0)) spectral densities have been determined for aroma tic deuterium nuclei in the side chains and their interpretation has been c arried out by means of several available motional models. The dynamic proce ss mainly contributing to relaxation has been found to be the rotation of t he phenyl ring about its para-axis, that is best described by a small step rotational diffusion model, where the diffusion constant has an Arrhenius t emperature dependence and a Gaussian distribution of the activation energie s is present, indicating a remarkable degree of dynamic heterogeneity of th is system. (C) 2001 Elsevier Science BN. All rights reserved.