Magnetic field induced alignment of the directors of a smectic-A liquid crystal

Deuterium NMR is used to monitor the magnetic field induced alignment of the directors in the smectic A phase of 4-octyl-4(')-cyanobiphenyl. The experiments consist of first preparing the sample as a monodomain by cooling slowly from the nematic phase in the magnetic field of the NMR spectrometer. The tube containing the sample is then rotated quickly through an angle theta(+), and the subsequent field induced alignment process followed by recording deuterium spectra over a period of time. The results obtained show that the magnetic field induced alignment of the directors in a smectic-A sample is qualitatively different from that of nematic samples. Results are reported for the pure mesogen containing deuteriums at the alpha chain position, and these are compared with data obtained on the alignment process by monitoring the deuterium spectrum of a small amount of an added solute, p-xylene-d(10).