Phase separation of monomer in liquid crystal mixtures and surface morphology in polymer-stabilized vertical alignment liquid crystal displays

Abstract

The polymer-stabilized vertically aligned (PS-VA) liquid crystal display (LCD) driving mode has high potential for manufacturing low power consuming displays due to the higher transmittance and fast response as compared with the existing patterned vertically aligned and multi-domain vertically aligned modes. In this paper we have investigated the reaction mechanisms of monomer–liquid crystal blends to form a surface pre-tilt angle of liquid crystal in vertical alignment LCD associated with a fishbone electrode structure. The observed sizes of polymer bumps formed on the substrates were found to be dependent on the exposed UV wavelength and were almost equal in both top and bottom substrates. When a large UV wavelength was used, the phase separation mechanism of monomer in PS-VA mode was found nearly isotropic rather than anisotropic in contrast to the previous studies.

Ordering kinetics of a conserved binary mixture with a nematic liquid crystal component

“…The systems involving liquid crystals are investigated via simulation [47,53,31,45,11] and the phase diagram indicating where transitions between the nematic and isotropic phases of the liquid crystal occur is analyzed [47,53,40]. Recently, applications of models for similar systems include polymer-dispersed liquid crystals [44,1,34,48,19,21,22,39,29], diblock copolymers [32,46], and other cases of problems involving phase separation [5,27,33,38,6,41,42,61].…”

Role of Monomer Alkyl Chain Length in Pretilt Angle Control of Polymer-Stabilized Liquid Crystal Alignment System

“…Whereas pretilt angle control with polymer has been comprehensively studied, the mechanism is still disputable. One hypothesis implies that the polymer network traps and “freezes” LC molecules in position during polymerization reaction, and these molecules keep their configuration and affect their neighbors onward. ,, This theory well explains why LC molecules must be aligned before polymerization. Another theory suggests that the polymer film modifies the surface property, and thus the pretilt angle changes.…”

“…In general, pretilt angle results from the interaction between LC molecules and alignment film surface, which is subject to surface chemical properties, molecular structure of LC, surface morphology, and so on. There are several methods that have been developed for tuning LC pretilt angle in the cell, including using polymer alignment layer with long alkyl side chains or nonpolar groups, − tuning rubbing conditions, , application of surface modification, − or utilization of composite and new material alignment film. − Among numerous techniques, polymer-stabilized LC is one of the most promising methods. − To control the pretilt angle, monomers are doped into the LC solution. Polymerization is triggered while LC molecules are subjected to electric field, which guides the molecules into uniform alignment.…”

Photo-Induced Vertical Alignment of Liquid Crystals via In Situ Polymerization Initiated by Polyimide Containing Benzophenone

“…Improved electro-optical properties and image quality, with a higher light transmittance, a lower rising time, and a lower operating voltage, were reported in PSVA LCDs. Many kinds of UV-curable monomers were used to realize PSVA, including reactive mesogen [ 1 , 19 , 20 , 21 ], long alky monoene, and polyene [ 22 , 23 ]. In the meantime, photoinitiators were added to obtain a fast reaction rate.…”