Determination of the director distribution in a nematic slab by simulation of the deuterium NMR spectra

Deuterium Nuclear Magnetic Resonance (NMR) spectroscopy has been widely used to study liquid crystals and is now considered to be a powerful method with which to investigate the director orientation and its distribution because the quadrupolar splitting observed in a spectrum is related to the angle made by the director with the magnetic field. It is possible to determine whether the director distribution is a monodomain or not from the spectral lineshape. In addition, the lineshape reflects how the director distribution varies in space. However, it is difficult to visualise the director distribution from the lineshape.We have studied how to determine the director distribution directly from the lineshape of the experimental NMR spectrum. The best fitted spectrum, which was assumed to have a Gaussian lineshape, to those measured were simulated using two adjustable parameters, the average director orientation and the standard deviation for the director distribution.The simulated spectra showed a good agreement with the experimental results. It is clear from the simulation of the director distribution that in the presence of magnetic and electric fields the director is a monodomain.