Computer Simulation of the Deuterium NMR Spectra Reflecting the Director Distribution for Multi-Domains in a Thin Nematic Cell

Abstract

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, reflects 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 lineshape varys with the director orientation. As well as being of practical relevance, when the director distributes thermally with the average director orientation in multi domains, this contribution to the lineshape is of fundamental interest for nematic behaviour. Here we explore ways to vary the aveage director orientation using an electric field and employ this to measure the voltage dependence of the NMR lineshapes for the nematic phase of 5CB-d₂. This approach is investigated by using a computer simulation of the NMR lineshapes.

Keywords:

• Deuterium NMR
• director distribution
• director orientation
• liquid crystal

A part of this work was supported by the HRC project (MEXT.HAITEKU 2006–2010) of the Ministry of Education, Culture, Sports, Science and Technology of Japan.