A uniform π-twist liquid crystal (LC) alignment was stabilized in a pi cell by photopolymerization of a minute amount of monomers without using any chiral material. Controlling UV exposure time can vary the LC pretilt angle to achieve a stabilized π-twist state. This type of π-twisted LC cell made using the polymer-sustained alignment has a pretilt angle estimated to be ∼20°. This cell can quickly transform into a bend state at a low driving voltage and shows excellent brightness and optical contrast, as compared with a conventional pi cell and a chiral-doped cell.
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.
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