Soon Bum Kwon

Photosensitive Materials on a Base of Polysiloxane for the Alignment of Nematic Liquid Crystals

The light-induced alignment of a number of commercial liquid crystals (LC) on the surface of photosensitive polysiloxane based polymers was studied. It was shown that the materials can provide thermostable homeotropic, planar and tilted alignments of good quality. The value of tilt angle depends upon the LC material, irradiation intensity and exposure as well as aligning film thickness and temperature treatment.

Electrooptic Response of Reflective-Mode, π/4-Twisted-Nematic Liquid Crystal Cell in the Voltage Regions Close to and Distant from the Freedericksz Transition Threshold

Two reflective-mode, π/4-twisted-nematic liquid crystal cells were prepared using E7 and ZLI 4801-000 liquid crystals and their electrooptic responses were measured in the voltage regions close to and distant from the Freedericksz transition threshold. Our reflectivity data distant from the threshold voltage (Vth) could not be described by the model that assumed a linearized distribution of the twist angle across the cell and considered the voltage dependency of the tilt angle to follow the equation suggested by Lu and Saleh [Appl. Opt. 30 (1991) 2354], although the fit is good near Vth. We determined that the reflectivity in the voltage region distant from Vth should be calculated using the model that considers the distributions of the tilt angle and the twist angle. The director-axis distributions were obtained from the numerical integration of the Ericksen-Leslie equation.

Evaluation of the electro-optic response of reflective liquid crystal cell

Abstract The electro-optic properties of the reflected light in a reflective mode, 45°-twisted nematic liquid crystal (TNLC) cell were investigated in the voltage regions near and away from the Freedericksz transition threshold. The measured reflectivity away from the threshold voltage ( V th ) could not be described by the model which assumes a constant tilt angle as well as a linearized distribution of twist angle across the cell, although the data are well fitted near V th . We found that in the voltage region away from V th , the model considering the distributions of the tilt angle and the twist angle should be applied for the calculation of the reflectivity. The director-axis distributions were obtained from the numerical integration of the Euler–Lagrange equation.