Hyundae Hah

Ultraviolet embossed alignment layer for flexible liquid crystal display

Ultraviolet (UV) embossed alignment layer for the flexible liquid crystal display (LCD) was fabricated to prevent problems encountered with the thermal treatment of the rubbing process on the plastic substrate. The mechanical stability against bending deformation was achieved by a phase-separated polymer wall. In a bent environment, the UV embossed alignment layer for the flexible LCD provided good liquid crystal properties and mechanical stability.

Ultraviolet embossed alignment layers having patterned spacers for flexible liquid crystal display

Ultraviolet (UV) embossed alignment layers having patterned spacers for the flexible liquid crystal display (LCD) were designed and fabricated to prevent the problems caused by residual monomers in photopolymerization-assisted manufacturing of liquid crystal (LC) devices. UV embossed alignment layers with patterned spacers provided mechanical stability and better alignment properties of LC molecules in a bent environment, compared with LC device with the phase-separated polymer walls. In the patterned spacers of UV embossed LC cell, the column-shaped spacer which has isotropic configuration of spacers provided good LC alignment during bending process.

Effect of photoreactivity of polyimide on the molecular orientation of liquid crystals on photoreactive polymer/polyimide blends

We prepared blend alignment layers from polymethacrylate with coumarin side chains (PMA-g-coumarin) and polyimides for the orientation of liquid crystals (LCs) using linearly polarized ultraviolet (UV) irradiation. We used two different polyimides, namely 4,4′-(hexafluoro-isopropylidene) diphthalic anhydride-3,5-diamino-benzoic acid (6FDA-DBA) and pyromellitic dianhydride-4,4′-oxydianiline (PMDA-ODA). It was found that the molecular orientation of the LC depended on the type of polyimide in the blend alignment layer. The thermal stability of the LC orientation was enhanced regardless of the type of polyimide, while the direction of LC orientation was different for each type of polyimide. The photoreactivity of the polyimide was a very important factor in determining the molecular orientation of the LC on the blend alignment layer. This may be attributed to the different mechanisms of LC orientation on PMA-g-coumarin and polyimide induced by the polarized UV irradiation. The direction of the LC orientation could be changed by controlling the photoreaction of the polyimides using the appropriate UV filter for the polarized UV irradiation.

Effect of Plasticization of Poly(Vinyl Cinnamate) on Liquid Crystal Orientation Stability

A cinnamate group is a well-known compound group used in the dimerization reaction by ultraviolet irradiation, and cinnamate polymers are studied as photoalignment materials. In this study, the radical reaction of cinnamate side groups attached to a flexible polymer backbone is considered feasible using thermal energy. To induce the thermal reaction of cinnamate side groups, we modified the flexibility of poly(vinyl cinnamate) by introducing a plasticizer into the polymers and investigated the thermal reaction behavior of cinnamate side groups. The plasticization of poly(vinyl cinnamate) makes the induction of the thermal reaction of cinnamate side groups easier than that of unmodified poly(vinyl cinnamate). The thermal reaction of cinnamate side groups is closely related to the enhancement of the thermal stability of the liquid crystal orientation of polymer films with polarized UV irradiation.

P‐171: Effect of Plasticization of Poly(Vinyl Cinnamate) on Liquid Crystal Orientation Stability

A cinnamate group is a well-known compound group used in the dimerization reaction by ultraviolet irradiation, and cinnamate polymers are studied as photoalignment materials. In this study, the radical reaction of cinnamate side groups attached to a flexible polymer backbone is considered feasible using thermal energy. To induce the thermal reaction of cinnamate side groups, we modified the flexibility of poly(vinyl cinnamate) by introducing a plasticizer into the polymers and investigated the thermal reaction behavior of cinnamate side groups. The plasticization of poly(vinyl cinnamate) makes the induction of the thermal reaction of cinnamate side groups easier than that of unmodified poly(vinyl cinnamate). The thermal reaction of cinnamate side groups is closely related to the enhancement of the thermal stability of the liquid crystal orientation of polymer films with polarized UV irradiation.

Thermal Reaction of Cinnamate Oligomers and Their Effect on the Orientational Stability of Liquid Crystals

Cinnamate groups are well-known for a dimerization reaction upon exposure to ultraviolet irradiation and a thermal reaction after being heated. In this study, to verify the thermal reaction of the cinnamate group in detail, we investigated the thermal crosslinking of cinnamate oligomers. The thermal reaction of cinnamate oligomers of low molecular weight is induced more readily by thermal energy compared with that of cinnamate polymers. This reaction is attributed to a radical reaction involving the carbon-carbon double bond in the cinnamate group. The orientation of the liquid crystal depended on the length of the spacers in the cinnamate oligomers.