A Pulsed NMR Study of Ionic-Conduction Induced Flow Alignment in Nematic Liquid Crystals

Nematic liquid crystals with negative dielectric anisotropies align with the nematic director approximately parallel to a low frequency electric field due to the presence of ionic impurities. The movement of these ionic impurities produces shear in the medium. Theoretical expressions for hydrodynamic flow in the presence of shear predict that the nematic director will rotate to make a small angle with respect to the direction of shear flow. Nuclear magnetic resonance techniques are used to determine both this “flow alignment angle” and to determine the molecular order and orientation as a function of time after the sudden application of an electric field.