Study of Twisted Optically Compensated Bend Cell Using Patterned Alignment

Abstract

We have investigated a new liquid crystal cell based on a nonchiral-doped optically compensated bend (OCB) mode. The average pretilt angle of this cell was higher than that of a conventional OCB cell; when undisturbed, the twist-to-splay energy barrier induced by topological differences remained in a twist state. We have called this twisted cell a twisted optically compensated bend (TOCB) cell. The TOCB cell does not require any warm-up time or warm-up voltage in electrical driving, and the response time of the TOCB cell was as fast as that of a conventional OCB cell. In this study, the TOCB cell was made using a polymer network pattern with high-pretilt-angle alignment, called a patterned-TOCB cell. The patterned-TOCB cell arose from the irradiation of UV light through a photomask and onto a pi cell, which was filled with nematic liquid crystal (NLC) and UV-curable polymer mixture upon a curing voltage being applied to it.

Electro Optical Characteristics of High-Pretilt Twisted Liquid Crystal pi-Cells

“…Calculation of the energy barrier is complicated and cannot be simulated by the current software, but experimental results confirm that the S state can be eliminated by increasing the substrate pretilt angle to 20 . 6,7) This means that the OCB cell can be stabilized in the T state and becomes a twist-stabilized optical compensated bend (TOCB) cell. The phenomenon was observed under a polarizing microscope, and a photograph was taken under a crossed-polarizer condition.…”

“…A TOCB cell has a lower pretilt angle ($20 ) than that of an NBB cell ($47 ) but higher than that of a conventional OCB cell (2-6 ). 6,7) The advantage of the TOCB cell is that it needs no warm-up time or warm-up voltage. In addition, a TOCB cell responds as fast as a conventional OCB cell.…”

“…This result is qualitatively the same as the experimental results shown in the inset. 7) In the experiment, the pretilt angle was controlled by a UV-curable monomer. A curing voltage was applied to the OCB cell during the UV curing process; therefore the pretilt angle increases as the curing voltage increases.…”