Pe Dunn

X-ray study of the layer structure in a high pre-tilt, anti-parallel aligned ferroelectric liquid crystal

Abstract X-ray diffraction has been used to investigate the layer structure of a ferroelectric liquid crystal device as a function of temperature. Obliquely evaporated silicon monoxide alignment layers arranged anti-parallel to each other were used to align a 2μ sample of racemic SCE13. In the smectic A phase, the cell formed a uniform tilted layer with a tilt angle in good agreement with the 25° pre-tilt of the SiO. Below the transition to Smectic C there was evidence for a highly asymmetric chevron with layers oriented away from the preferred alignment plane, together with domains of uniformly tilted layers. Further cooling to 30°C caused the chevron structure to disappear, until only the uniformly tilted layer remained.

The physics of τVmin ferroelectric liquid crystal displays

Abstract A theoretical model has been developed that allows predictions of the electro-optic behaviour for ferroelectric liquid crystal devices. As well as the ferroelectric polarisation and simple viscosity term, the model incorporates a surface anchoring energy, four elastic constants, the full biaxial electric tensor, and a critical switching torque to simulate domain nucleation at the chevron interface. Not only is this model at the heart of the measurement methods for many of the important parameters, it also provides an invaluable tool for the design of displays. Experimental results of the switching characteristics of a material operating in the τVMIN mode are fit by the theory.

X-RAY STRUCTURAL STUDIES OF FERROELECTRIC LIQUID CRYSTAL DEVICES

X-ray diffraction from smectic materials in device-like cells is used to determine the layer structure within the cells. The experimental method determines the smectic layer normal orientational distribution as a function of tilt and twist angles within the cell. In a special case where the layer normals are not twisted away from the alignment direction, the chevron structures have been reconstructed from the distributions. The influence of the surface pre-tilt due to the alignment layer, electric fields and skewed alignment layers on the smectic layer normal distributions are reviewed and discussed.

X-ray studies of layer structure and needle defects in anti-parallel aligned SSFLC devices with medium pre-tilt

Abstract X-ray diffraction has been used to investigate the structure of ferroelectric Smectic C* (SmC*) devices with anti-parallel orientation of the alignment layers. The layer structure during cooling from the Smectic A (SmA) phase has been determined for three different surface pre-tilts. The results are presented as two-dimensional layer normal distributions that show in detail the changes in layer orientation as a function of temperature. For low and medium pre-tilt surfaces a transformation from a uniformly tilted layer in the Sm A to a chevron in the Sm C was observed in monodomain regions. These surfaces also tended to show needle defects in the Sm C and their layer structure is discussed.

Determination of the Temperature Dependent Smectic C Biaxial Permittivity Tensor and Elastic Constants

Abstract The direct measurement of the smectic C bend (B1) and splay (B2) elastic constants and the three permittivities e1, e2 and e3 for the commercial material SCE8R is described. A new technique has been employed in which some of the assumptions inherent in previous measurements[1,2] have been removed and the inaccuracies have been reduced. This involves fitting the a.c. field dependence of the permittivity in the surface stabilised chevron (C2U) geometry using continuum modelling. Data from the fitting process is combined with measurements of the homeotropic permittivity and electro-optical measurements of the layer tilt angle and smectic cone angle.