Soo In Jo

Surface-controlled patterned vertical alignment mode with reactive mesogen

We proposed a patterned vertical alignment (PVA) mode controlled by a modified surface with ultraviolet (UV) curable reactive mesogen (RM) mixed with vertical alignment material for a liquid crystal display (LCD) with fast response time. In the surface-controlled PVA (SC-PVA) mode, the RM monomers in the alignment layer are polymerized along the LC directors by UV exposure under an applied voltage. The polymerized RMs produce a pretilt against the substrate normal depending on the applied field direction in the patterned electrode configuration. In such SC-PVA mode, fast response time was achieved at whole grey levels with the predetermined rotational preference of the LC directors governed by the pretilt direction.

Control of liquid crystal pretilt angle by anchoring competition of the stacked alignment layers

We proposed a method to control the pretilt angle of liquid crystals by stacking of a vertical alignment layer on a planar alignment layer. The pretilt angle can be controlled over the full range (0°–90°) depending on the thickness of the vertical alignment layer. We also proposed a numerical model to describe the physical mechanism based on the anchoring competition between liquid crystal, planar, and vertical polyimide alignment layers.

Inverse four-domain twisted nematic liquid crystal display fabricated by the enhancement of azimuthal anchoring energy

An inverse four-domain twisted nematic (IFDTN) liquid crystal (LC) display was fabricated by enhancing the azimuthal anchoring energy of the alignment layers. By stacking a vertical alignment layer onto a planar alignment layer, we increased the azimuthal anchoring energy by approximately 17-fold times compared to that with vertical alignment only. Due to the enhanced azimuthal anchoring energy, we were able to achieve a four-domain twisted nematic LC structure without dopant via the application of an external voltage. A simulation of the LC molecular orientation with respect to the azimuthal anchoring energy, the viewing angle characteristics, and the switching behavior of the IFDTN LC are presented.

Direct image of a molecular orientation of a liquid crystal using directional polymerization of photoreactive mesogen

We present a method for visualizing the geometrical distribution of a liquid crystal (LC) arrangement using the replication of the molecular orientation by a mixture of alignment layers. We found that the anisotropic diffusion of the reactive mesogen (RM) monomers, mixed with an alignment layer, in contact with the LC was governed by the LC director through application of external voltage and allowed the directional polymerization under ultraviolet light illumination. The directional polymerization of a RM transferred and visualized the LC arrangement even at optically indistinct LC distributions.

Effects of surface modification with reactive mesogen on the anchoring strength of liquid crystals

We studied the effects of polymer chain ordering in the alignment layer and resulting molecular interactions on the surface anchoring energy by introducing a reactive mesogen (RM) coating to the alignment layer. Directionally polymerized RMs on the rubbed alignment layer decrease the steric repulsion and increase the electronic interaction with liquid crystal molecules, and, as a result, the surface anchoring energy is enhanced in both the out-of plane and in-plane directions. We also demonstrated that this enhanced surface anchoring energy can be used to improve the response time characteristics of liquid crystal displays.

Fast Eight-Domain Patterned Vertical Alignment Mode with Reactive Mesogen for a Single-Transistor-Driving

We proposed a wide-viewing patterned vertical alignment (PVA) mode with eight-domains driven by a single transistor. The eight-domain PVA mode was fabricated by introducing two different pretilt angles in a pixel using polymerized reactive mesogens (RMs) within alignment layer. The pretilt angles are simply controlled by an applied voltage during illumination of ultraviolet light for polymerization of the RMs. In addition, the polymerized RMs give rise to defect-free transition in our advanced PVA mode and thus fast response can be achieved over whole grey level.

45.1 Fabrication of Fast Switchable Patterned Vertical Alignment Mode Using Modified Surface with Reactive Mesogen

We proposed a new fast switchable patterned vertical alignment (PVA) mode using UV curable reactive mesogen (RM) which was mixed with vertical alignment layer. In this mixed alignment layer, the pretilt angle was controlled according to an applied voltage during UV exposure for curing the RM. As a result, the response time was dramatically improved at the whole grey levels by controlling the pretilt angle in conventional PVA mode.

Temperature-independent pitch invariance in cholesteric liquid crystal.

We report a pitch invariance in cholesteric liquid crystals (CLCs) independent of temperature by mixing two chiral dopants. One dopant tends to shorten the helical pitch of the CLC, but the other makes the pitch longer, with increasing temperatures. From an analysis of temperature dependencies of the pitch for each dopant, we determined the mixing ratio of two chiral dopants for the pitch invariance. Finally, we obtained the pitch-invariant CLCs to temperature and the helical twisting power of the mixed dopant was estimated.

Highly polarized emission of the liquid crystalline conjugated polymer by controlling the surface anchoring energy

We demonstrated a highly polarized organic light-emitting diode (OLED) through the enhancement of the orientational ordering of the emitting polymer with a nematic liquid crystalline (LC) phase. The highly ordered state of the conjugate polymer was obtained by thermal annealing at the nematic temperature and strong azimuthal anchoring energy of the underlying polyimide. The order parameter of the conjugate polymer was analyzed using a second-harmonic generation model and the dichroic ratio was measured to be 22 : 1. Also, we applied our optimized OLED with high optical polarizability to an effective light source for a twisted nematic LC display.

Viewing angle controllable liquid crystal display under optical compensation

We investigated a viewing angle control of a liquid crystal display (LCD) under optical compensation for the enhancement of viewing angle characteristics in a wide viewing angle mode. The viewing angle controllable (VAC) LCD was operated in the configuration of three terminal electrodes consisting of a fringe-field-switching electrode at a bottom substrate and a common electrode at a top substrate. Using Poincare sphere analysis, the optical compensation for the VAC LCD was designed so that the viewing angle characteristics were much improved in the wide viewing mode while they were degraded in the narrow viewing mode.