Pixel-isolated Liquid Crystal Research Articles

Pixel-Isolation Walls of Liquid Crystal Display Based on Prepolymer Containing Vinyl Cinnamate

Pixel-isolated liquid crystal (PILC) mode investigated in this work is obtained by phase separation induced by the anisotropic photoreaction of a prepolymer containing a vinyl cinnamate monomer. It was found that the incorporation of the cinnamate monomer was an efficient method for the control of the interfacial properties between LC and polymer walls. Polarization-selective photo-curing of the prepolymer containing a cinnamate monomer was closely related with the liquid crystal orientation at the polymer wall boundary resulting in electro-optical performance improvement.

The effect of bi-component acrylate prepolymers on the phase separation and electro-optical properties of pixel-isolated liquid crystals

In this paper, we propose a pixel isolated liquid crystal (PILC) display using prepolymers containing bi-component acrylate monomers. The phase separation behavior and polymer wall structure of PILC were closely related to the solubility parameter and surface free energy of acrylate monomers. The polymer wall structure of bi-component prepolymers was readily controlled by the composition of acrylate monomers. We also investigated the electro-optical performances of PILC devices prepared by using bi-component prepolymers and found that they were related with the surface anchoring effect of polymer walls. Anchoring energy between LC and polymer walls was decreased by introducing fluorinated acrylate monomer into prepolymers and the driving properties of LC molecules by an external electric field were improved. Thus, the control method of polymer wall structure by using bi-component prepolymers can be applied to various types of LC–polymer composite systems for obtaining improved flexible displays.

Pixel-isolation liquid crystals formed by polarization-selective UV-curing of a prepolymer containing cinnamate oligomer

A pixel isolated liquid crystal display was fabricated by polarization-selective anisotropic photoreaction of a prepolymer containing a cinnamate oligomer. The cinnamate oligomer was mainly distributed on the surface region of a UV-cured polymer wall. Anisotropic photo-dimerization of cinnamate moiety was achieved by polarized UV exposure. It was found that the polymer walls containing cinnamate dimers formed by polarized UV exposure showed ordered orientation of LC molecules at the boundary of the polymer walls resulting in electro-optic performance improvement.

P‐119: The Stabilized Bistable LC Mode for Flexible Display from Multi‐rubbing on the PILC Structure

AbstractWe propose the stabilization technique for the memory state of bistable liquid crystal (LC) mode in the pixel‐isolated LC (PILC) structure. To obtain the enhanced retention time of memory state, we apply the multi‐rubbing method to create the partial 90° twisted domains in each sub‐pixel as the seeds of stabilizing the π‐twist states. The PILC structure provides the uniform and stable cell gap against various external deformations. The suggested structure can be very useful for portable flexible display applications with high quality device performance such as low power consumptions and good mechanical reliability.

Pixel‐isolated liquid‐crystal mode by using a patterned anisotropic phase separation for flexible LCDs

Abstract— A pixel‐isolated liquid‐crystal (PILC) mode for enhancing the mechanical stability of flexible‐display applications is proposed. Because liquid‐crystal (LC) molecules in this mode are isolated in each pixel by patterned or phase‐separated microstructures, and the two substrates are tightly attached to each other by a solidified polymer layer, the LC alignment is stable against external pressure, and the cell gap of our structure is uniformly preserved against bending deformation of the plastic substrates. The mechanical stability of the PILC structure having plastic substrates was tested for its electro‐optic properties.

Mechanical Stability of Pixel-Isolated Liquid Crystal Mode for Flexible Display Application

We have fabricated the Pixel-Isolated Liquid Crystal (PILC) mode using micro-supporting structures and anisotropic phase separation method. Since the cell gap is sustained by polymer walls and the phase separated polymer layer, this novel structure shows good electro-optic properties having stability against external mechanical distortion. The mechanical stability of this configuration against external forces like pressure and bending is confirmed to be useful for diverse flexible display applications.

56.2: Invited Paper: Pixel-Isolated Liquid Crystal Mode for Plastic Liquid Crystal Displays

Abstract We proposed a pixel-isolated liquid crystal (PILC) mode for enhancing mechanical stability of flexible display applications. Since the LC molecules in this mode are isolated in pixels by patterned or phase-separated microstructures, the LC alignment is stable against external pressure. Moreover, the cell gap of our structure is uniformly preserved against bending deformation of the plastic substrates since two substrates are tightly attached each other by the solidified polymer layer produced by photo-induced anisotropic phase separation. For flexible display applications, we have tested the mechanical stability of electro-optic properties in PILC structures with plastic substrates. 1. Introduction In recent years, roll-up displays have drawn considerable attention for next-generation information displays because of their excellent portability such as light weight, thin packaging, and flexibility. Among several available technologies, it is expected that a liquid crystal display (LCD) using plastic film substrates is the most promising device because of its superior visibility with low power consumption over other displays such as organic light-emitting device or electrophoretic displays. However, there are still critical problems regarding the fabrication of commercially available plastic LCDs with current technologies based on the glass substrates. One of those problems is the instability of LC structures due to hydrodynamic properties of LCs at bending and another is the separation of two plastic substrates due to the flexibility of film substrates. Such problems do not exist in conventional glass-substrate-based LCDs since glass substrates can sustain a stable LC alignment condition against external bending or pressure. To solve these problems, several types of polymer wall and/or network as supporting structures have been proposed and demonstrated [1]-[7]. These structures were fabricated using an anisotropic phase separation method from polymer and LC composite systems by applying a patterned electric field or spatially modulated UV intensity. However, these methods require high electric field to initiate the anisotropic phase separation or remain residual polymers in unexposed regions that reduce optical properties and increase the operating voltage of the devices.

Mechanical Stability of Pixel-Isolated Liquid Crystal Mode with Plastic Substrates

We have fabricated a plastic liquid crystal display using the pixel-isolated liquid crystal (PILC) mode and characterized the mechanical stability of the sample against mechanical pressure and bending. Since the liquid crystal molecules are fully isolated in the pixels by the phase-separated polymer walls in the PILC mode, the electrooptic properties of the sample show good mechanical stability. In addition, a polymer layer formed on the upper substrate enhances the adhesion between two plastic substrates.