Photoalignment Materials Research Articles

P‐67: Applications of New Photoalignment Materials Containing Cinnamoyl Group

AbstractLiquid crystal alignment performance of a series of polymethacylate based photopolymers containing cinnamoyl group and their applications have been investigated. By illuminating linearly polarized UV light on the film of the photopolymers, strong azimuthal anchoring energy was induced and liquid crystal alignment on the photopolymer film was thermally stable up to 150 °C. Photochemical stability appeared to be dependent on the mode of alignment. Pretilt angle was controllable from 0 to 90 degree by changing the amount of UV dose, incident angle, parameters of liquid crystal, along with slight structural modifications of the photopolymer. Applications to current LCD modes such as TN, VA, IPS, STN and the film application for phase compensation and retardation have also been studied.

P‐66: New Photo‐Alignment Technology Based on Chalcone Moieties: Molecular Design and Process Development

AbstractIn this paper, factors affecting the pretilt angle are investigated for our newly‐developed photo‐alignment materials. We believe that two factors are crucial for the pretilt angle generation. That is, surface tension of the alignment films, and the incident angle of the LPUV light which may affect the surface order degeneracy. In addition, our development efforts of the photo‐alignment materials will be shortly summarized.

45.1: New Photo‐Alignment Technology For IPS‐LCDs

AbstractThis paper describes a new photo alignment technology for in‐plane switching liquid crystal display (IPS‐ LCDs). We studied a new photo alignment technology with photo‐alignment material called PMI‐A, which based on ω ‐(4‐Chalconyloxy) Alkyl side group on both the styrene units and phenylmaleimide units. One order of magnitude enhancement anchoring strength can be realized on PMI‐A, achieving zero pretilt angle. On other hand, it is difficult to achieve the pretilt angle of zero degree by the rubbing method. Furthermore, it is confirmed that when this photo alignment technology is utilized for IPS‐LCDs, the image sticking and the electro‐optical properties are improved. We think that the PMI‐A film is more suitable than the rubbing film for IPS‐LCDs.

Effects of the cinnamoyl group on liquid crystal aligning capabilities on PCEMA surfaces

Four kinds of poly(4-methacryloyloxychalcone) (PCEMA) photo-alignment materials were synthesized. The effect of the cinnamoyl group on liquid crystal (LC) aligning capabilities and electro-optical characteristics of photo-aligned twisted nematic (TN) liquid crystal displays (LCDs) was investigated by photo-dimerization. Uniform NLC alignment by linearly polarized UV exposure at normal incidence on the PCEMA surfaces having a high density of cinnamoyl groups was observed. Also, excellent voltage-transmittance (V-T) curves for the photo-aligned TN-LCDs on the PCEMA surfaces was achieved. We find that the V-T and response time characteristics can be improved by increasing the density of cinnamoyl groups.

Material Design for Application to High Performance LCDs.

Liquid Crystal Display(LCD) is a high performance tool for displaying many kinds of information. Application of LCD is diversifying to notebook PC, monitor display, TV and reflective type of PDA and personal handy phone. To achieve these performance for several applications of LCD, development of new materials has been investigated. Color photoresist is used for color filter production. Negative and positive type of transparent photoresist are applied for leveling and overcoating layer of LCD process, and further used for spacer materials. For the next generation of alignment layer, photo-alignment material is also investigated. Dimerization of chalcone moiety showed good alignment characteristics for liquid crystals and good LCD performance.

Investigation of electro-optical characteristics of photo-aligned TN-LCDs on PCEMA surfaces

In this work, a novel photo-alignment material, poly(cinnamolyethyl methacrylate) (PCEMA), was synthesized by photo-dimerization. We investigated the electro-optical characteristics of twisted nematic (TN)-liquid crystal displays (LCDs) photo-aligned with linearly polarized UV light irradiation at normal direction on the PCEMA surfaces. Excellent voltagetransmittance characteristics were observed. The threshold voltage of the photo-aligned TN-LCD decreases with increasing UV irradiation time. Additionally, response times are almost the same as for a rubbing-aligned TN-LCD.

Electro-optical characteristics of photo-aligned TN-LCD on PM4Ch surface

In this study, a photo-alignment material PM4Ch, poly(4-methacryloyloxychalcone), was synthesized. The electro-optical characteristics of a photo-aligned twisted nematic liquid crystal display (TN-LCD), with linearly polarized UV exposure at normal direction on a PM4Ch surface, were investigated. The NLC alignment was uniform. Excellent voltage-transmittance characteristics were obtained; a fast response time was also achieved. Reduction of d.c. voltage decreases with increasing UV exposure time.

29.3: Low‐Molecular‐Weight Photo‐Crosslinkable Composites: Advanced Materials for Liquid Crystal Alignment

AbstractNew photoalignment materials, based on low‐molecular‐weight photo‐crosslinkable (LMWPC) composites, were developed and characterized. The LMWPC materials have advantages such as ease of synthesis, reduced alignment film preparation, and stable liquid crystal (LC) alignment; they are capable of a wide range of pretilt from planar to slightly tilted homeotropic. Such LMWPC materials are ideal alignment layers for all ranges of liquid crystal display (LCD) technologies including LCDs with patterned alignment and LCDs using plastic as substrates.

Novel Photoalignment Materials for Liquid Crystals Based on Modified Polysiloxane

Novel photosensitive alignment materials based on allyl-cinnamate-grafted methyl hydrogen polysiloxane fluid (MHPF) were used in fabricating liquid crystal (LC) cells by sandwiching nematic LC molecules between two indium-tin-oxide (ITO) patterned substrates. The LC aligning ability of this kind of alignment layer, fabricated by linearly polarized UV-induced polymerization (LPP), was characterized based on polarizing microscopic and conoscopic observations. The influences of the thickness of LPP films, LC materials, different end groups, baking conditions and exposure conditions on the alignment and thermal stability are discussed in detail. The results confirmed that the photoalignment films exhibited not only good aligning ability but also excellent thermal stability.

Key Molecular Structure Determination of Photoalignment Materials from the Effects of Linearly Polarized Deep UV Light on Several Polymers

We studied the photoalignment of nematic liquid crystals by examining polyimide, polyester, polystyrene, polyvinylalcohol (PVA), and polymethylmethacrylate (PMMA) exposed to linearly polarized deep UV (LPDUV) light. Polystyrene aligned the liquid crystal parallel to its LPDUV polarization axis, while polyimide and polyester aligned the liquid crystal perpendicular to the polarization axis. Polyimide and polyester exhibited order parameter peaks for small dosages of LPDUV. PVA and PMMA did not align the liquid crystal. The presence of a phenyl ring is a key to the decomposition-type photoalignment, whose alignment direction depends on the position of the phenyl ring.

LP‐3: Late‐News Poster: Photoalignment Materials Based on ω‐(4 ‐Chalconyloxy) Alkyl Groups Providing TN Alignment with Pretilt Angle by One‐Step Exposure of Polarized Near‐UV Light

AbstractNew photo LC alignment materials based on poly (ω ‐(4‐chalconyloxy) alkoxyphenyl maleimide) were synthesized and evaluated. On the films of these materials, LC alignment was regulated parallel to the polarization plane of the exposed LPUV at a large dose, and thus generated pretilt angle among 1–5° by one‐step slantwise LPUV exposure. TN cells were fabricated using these materials.

LP‐H: Late‐News Poster: New Photo‐Alignment Materials with High Sensitivity to Near‐UV Light

AbstractWe developed new photo alignment materials based on chalcone structure with the high photo reactivity and high sensitivity to near UV light. Poly(4‐methacryloyloxy chalcone), PM4Ch, and its derivatives exhibited good LC alignment capability upon near UV exposure. The LC alignment capability was preserved when the LC cells were annealed at 170°C. The possible photochemical degradation by deep UV can be prevented by using these new materials.

Photo Alignment Materials with High Sensitivity to Near UV Light.

We developed new photo alignment materials based on chalconyl structure with high sensitivity to near UV light. Poly(4-methacryloyloxy chalcone), PM4Ch, and its derivatives exhibited good LC alignment upon near UV exposure. The photoreactivity of chalconyl structure was high because due to longer wavelength of UV absorption. The high sensitivity of PM4Ch, compared with Poly(4′-methacryloyloxy chalcone), PMCh, could be explained by the suppression of isomerization and/or by the alignment capability of the side chain structure.