Deuterium NMR spectra of a monodomain nematic: Angular dependence of the linewidths

Deuterium NMR spectroscopy is widely employed to investigate the static and dynamic director alignment for low molar mass nematics contained in a thin sandwich cell. When the director is not uniformly aligned the appearance of the deuterium NMR spectra, recorded in the measurements, reflect the form of the director distribution. This occurs because the observed spectrum is a weighted sum of the spectra from all director orientations in the sample. In order to obtain the form of the director distribution function by simulating the spectra it is necessary to know how the spectral linewidths vary with the director orientation. As well as being of practical relevance, the angular dependence of the linewidths is of fundamental interest for nematic behaviour because it is related to factors such as molecular rotation, director fluctuations and orientational order. Here we explore ways to vary the director orientation, as a monodomain, using an electric field and employ this to measure the angular dependence of the NMR linewidths for the nematic phase of 4-α,α-d2-pentyl-4′-cyanobiphenyl as a function of temperature.