Rotational diffusion of asymmetric molecules in liquid crystals: A global analysis of deuteron relaxation data

A new global analysis of the relaxation data in the nematic and smectic A phases of 4-n-pentyloxybenzylidene-4'-heptylaniline [Phys. Rev. E 49, 538 (1994)] supports a model which includes director fluctuations and rotational diffusion of an asymmetric rigid rotor in a biaxial potential of mean torque. The molecular biaxiality of the molecule is found, based on the relaxation data, to give a small positive biaxial order parameter S-yy-S-xx. In addition, the activation energy for the tumbling motion of the molecule is found to be larger than that for the spinning motion. The usefulness of globally analyzing the deuteron relaxation data at different temperatures and frequencies is demonstrated. (C) 1996 American Institute of Physics.