Andrew Hitoshi Ohgaki

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-d(2). This approach is investigated by using a computer simulation of the NMR lineshapes.

Film thickness dependences of the unified surface anchoring strengths from the splay deformation for nematic cells were discussed. Thin nematic parallel (d=2-50 mu m) and wedge (d=0.3-5 mu m) cells with the same solid surface were prepared to evaluate the surface anchoring strength. The surface anchoring strengths from the splay deformations for two kinds of liquid crystals were measured by using the saturation method. The nematogens used were 4-pentyl-4'-cyanobiphenyl and mixture compound ZLI-4792 (Merck Japan Co., Ltd.) with positive dielectric anisotropy Film thickness dependence of the surface anchoring strength was elucidated on the basis of the conventional ionic surface polarization. It was also discussed that a surface anchoring strength from the splay deformation is to be an intrinsic value defined at an interfacial region and not a value changing with the film thickness. (c) 2007 Elsevier B.V. All rights reserved.

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. (c) 2007 Elsevier B.V. All fights reserved.

Deuterium NMR spectroscopy has been used to investigate the director dynamics in the smectic A phase of perdeuteriated 4-octyl-4 '-cyanobiphenyl-d(25) (8CB-dA(25)), where the director was aligned by an electric field. The electric field direction made an angle of 44.7 degrees with the magnetic field in order to provide a unique alignment pathway; accordingly the director is expected to rotate as a monodomain. When the electric field is applied to the nematic film, the director moves from being parallel to the magnetic field to being at an angle with respect to it. After the electric field is switched off, the director relaxes back to being parallel to the magnetic field. Deuterium NMR spectra were recorded during the turn-on and the tum-off alignment processes as a function of time. This particular technique was chosen because the spectral peaks associated with each rigid group in the molecule are clearly resolved and of comparable intensity. For all of the experiments at different temperatures in the smectic A phase of 8CB-d(25) We found that the relaxation times are independent of the group used to determine the director orientation during the alignment process as same as the results for the nematic phase. It also was found that the relaxation time in the smectic A phase is about 1,000,000 times as large as that in the nematic phase. This results in a strong pretransitional growth of the relaxation time as the transition to the smectic A phase is approached. (c) 2005 Elsevier B.V All rights reserved.