Field-induced director dynamics of nematic 4-octyl-4′-cyanobiphenyl:: A study by deuterium NMR spectroscopy

Deuterium NMR spectroscopy has been used to investigate the director dynamics in the nematic phase of perdeuteriated 4-octyl-4'-cyanobiphenyl-d(25) (8CB-d(25)) When the electric field is applied to the nematic film, the director moves from being parallel to the magnetic field to being at an angle with respect to it. After the electric field is switched off, the director relaxes back to being parallel to the magnetic field. Deuterium NMR spectra were recorded during the, turn-on and the turn-off alignment processes as a function of time. This particular technique was chosen because the spectral peaks associated with each rigid group in the molecule are clearly resolved and of comparable intensity. For all of the experiments at different temperatures in the nematic phase of 8CB-d(25) we find that the field-induced relaxation times are independent of the group used to determine the director orientation during the alignment process.