Dynamics of a liquid crystal in its smectic A phase from angle dependent deuterium spin relaxation measurements

The Zeeman and quadrupolar spin-lattice relaxation times of the aromatic deuterons of OAB-d(12) were measured throughout the smectic A phase at two different frequencies (15 and 46.04 MHz). At 15 MHz measurements were performed as a function of the angle between the phase director and the external magnetic field. Eight spectral densities were consequently determined, and were analyzed by means of a global target fitting procedure using diffusional models for the overall molecular reorientations and the internal motions. Diffusional coefficients of about 10(9) s(-1) were found for molecular spinning and phenyl ring rotations, three orders of magnitude higher than for molecular tumbling.