The effect of backflow on the field-induced director alignment process: Nuclear Magnetic Resonance study and theoretical analysis

The nature of the orientational relaxation process of the director, (n) over cap, to its equilibrium orientation, (n) over cap (eq)(r), in a liquid crystal cell has been investigated both experimentally and theoretically. The experiments employ deuterium NMR spectroscopy to investigate the time-resolved field-induced director orientation, and the theory is based on a numerical study of the system of hydrodynamic equations; these include both director motion and fluid flow and take account of backflow. The relaxation time and the influence of the effect of backflow on the orientational relaxation process for a thin nematic film of 4 - n - pentyl -4' - cyanobiphenyl has been investigated for a number of dynamic regimes. Reasonable agreement is observed between the calculated values and experimental results.