Anisotropic self-diffusion in the nematic phase of a thermotropic liquid crystal by H-1-spin-echo nuclear magnetic resonance

The orientation-dependent molecular diffusion in the nematic liquid crystal 4-pentyl-4'-cyanobiphenyl is measured to high accuracy. The applied nuclea r magnetic resonance method combines multiple-pulse homonuclear dipolar dec oupling with pulsed-field-gradient stimulated echo and slice selection. The obtained temperature dependencies of the principal diffusion coefficients are not described by a simple Arrhenius relationship but reflect the decrea se of the molecular orientational order close to the nematic-to-isotropic p hase transition. The geometric average of the principal diffusion coefficie nts is continuous with the diffusion coefficient in the isotropic phase. Th e results are best described in terms of the affine transformation model of diffusion in hard-ellipsoid nematics. (C) 2001 American Institute of Physi cs.