Rotational dynamics of a discotic liquid crystal studied by deuteron spin relaxation

We report on measurements of deuteron quadrupolar splitting and spin-lattic e relaxation times T-1Q and T-1Z in the columnar phase of a ring-dauteriate d hexaoctyloxyrufigallol at 46 MHz as a function of temperature. To describ e small-step rotations of these molecules within each column in the columna r phase, a space-fixed frame is used to diagonalize the molecular diffusion tensor. The principal diffusion constants in this so called 'anisotropic v iscosity' model D-alpha and D-beta are for rotations of a molecule around a nd perpendicular to the columnar axis, respectively. A global target analys is of the spectral densities at seven temperatures in a minimization proced ure was carried out. We found that D-alpha > D-beta, which is consistent wi th the picture that the motion towards or away from the local director tend s to disrupt the packing of molecules within the column.