Electric field-induced alignment of the directors in the smectic A phase of 4-octyl-4 '-cyanobiphenyl. A deuterium NMR study

Deuterium nuclear magnetic resonance (NMR) spectroscopy has been used to in vestigate the electric field-induced alignment of the director of the smect ic A phase of the liquid crystal, 4-alpha,alpha -d(2)-octyl-4'-cyanobipheny l (8CB-d(2)), at 303.3K. The electric field is arranged to be orthogonal to the magnetic field. The alignment process has been investigated at differe nt electric field strengths and the rate of director alignment was monitore d by recording the deuterium NMR spectra as a function of time after the el ectric field was switched on. The results reveal a complex pattern of elect ric field-induced director alignment. At high electric field strengths a ra pid process is observed in which the director switches from an orientation parallel to the magnetic field to one in which it is parallel to the electr ic field. An induction period is also observed in which no apparent change in director orientation occurs. This induction period becomes longer (hours in magnitude) as the electric field strength is lowered. Other, intermedia te, director orientations are observed as the electric field strength is lo wered further. The role of defects is invoked in trying to interpret some o f the observed processes underlying the mechanism of the director alignment in the smectic A phase.