Chein-Dhau Lee

Polymethacryloylaminoarylmethacrylates: New Concept of Photoalignment Materials for Liquid Crystals

New class of highly efficient polymers for liquid crystal (LC) photoalignment is proposed. These polymers are based on methacryloylaminoarylmethacrylates having two methacryloyl groups of different reactivity. The more active O-methacryloyl group is subjected to polymerization, while the less active NH-methacryloyl group undergoes photocrosslinking reaction in combination with Fries rearrangement. The latter process is anisotropic in case of polarized light irradiation that results in LC photoalignment with readily controlled pretilt angle and anchoring energy. The induced alignment shows high thermal and photo-stability.

New Photoalignment Materials in LCD's Development: Liquid Crystal Pretilt Angle Variations By Using Fluoroalkylmethacrylates

Fluorinated copolymers based on 4-(N-methacryloylamino)phenyl methacrylate are proposed as materials for the liquid crystal (LC) photoalignment with a wide range of variations of a pretilt angle. As fluorinated chains, 2,2,3,3-tetrafluoropropylmethacrylate and 2,2,3,3,4,4,5,5-octafluoropenthylmethacrylate are used. The growth of a pretilt angle with the concentration of fluorinated chains, more pronounced in a series with longer fluorinated chain, is observed. The pretilt angle of TN LC ZLI 2293 is smoothly varied in the range 0°–20°. Additionally, the uniform high pretilt angle (89°–90°) alignment is realized for VA LC MJ961180.

Mechanism in determining pretilt angle of liquid crystals aligned on fluorinated copolymer films

This work explores the surface treatment of copolymer materials with fluorinated carbonyl groups in various mole fractions by ultraviolet irradiation and ion-beam (IB) bombardment and its effect on liquid crystal (LC) surface alignments. X-ray photoemission spectroscopic analysis confirms that the content of the grafted CF2 side chains dominates the pretilt angle. A significant increase in oxygen content is responsible for the increase in the polar surface energy during IB treatment. Finally, the polar component of the surface energy dominates the pretilt angle of the LCs. (Some figures in this article are in colour only in the electronic version)

The Multimode LC Alignment on the Substrates Obliquely Treated with a Plasma Flux

ABSTRACT We describe a variety of liquid crystal (LC) alignment modes on the aligning substrates obliquely treated with a flux of accelerated plasma from the anode layer thruster (ALT). The discharge area has a form of race track so that the generated flux contained two sheets of plasma corresponding to linear parts of the discharge. Within each “sheet” the intensity of flow (ion current density) is uniform in the direction parallel to the linear part of discharge. Across the “sheet”, the intensity of flow has the Gaussian distribution. The alignment of LC with positive and negative dielectric anisotropy, Δϵ, was tested on the substrates of organic (polymers) and inorganic (glass and DLC) origin treated in static and dynamic regime (unidirectional translation perpendicularly to plasma “sheet”). In the dynamic regime of irradiation, with the substrate moving with respect to the plasma beam, for LC with Δϵ > 0 we observed two aligning modes, with the easy axis confined to the plane of plasma incidence (mode 1) or perpendicular to this plane (mode 2). In the 1st aligning mode the LC pretilt angle is non-zero and can be varied with the incidence angle of plasma beam and the irradiation dose. With the increase of irradiation dose, the alignment transition from the 1st to the 2nd mode occurs. For LC with Δϵ < 0 only the 1st alignment mode uniform over all substrate was observed. In the static regime of irradiation, characterized by smooth distribution of the particles flow across the sheet, two modes are clearly observed simultaneously; 2nd mode alignment occurs in central, most intensive part of flow, while the periphery part shows the 1st mode. The areas of the 1st and the 2nd mode are separated with the narrow transition area showing multidomain (two-fold degenerate) LC alignment. The easy axis in these domains is turned by about ±45° with respect to the alignment direction in the 1st mode area. This sequence of the alignment transitions is observed in both LC with Δϵ > 0 and Δϵ < 0. We also describe a high-tilt alignment (87°–90°) in the 1st mode realized on the hydrophobic polymers at the extremely low doses of plasma irradiation. The origin of the observed alignment effects is discussed.

Surface Alignment with High Pretilt Angle Using the Photoreactive Fluorinated Polymer Films

A newly developed fluorinated polymer film for liquid crystal alignment by applying ultra-violet (UV) irradiation or ion beam treatment is studied in this work. The surface alignment with high pretilt angle is achieved by the UV treatment. The induced pretilt angle by ion beam treatment on this photo-reactive polymer film, however, is relatively small. Surface analyses by x-ray photoemission spectroscopy and contact angle measurement are carried out to deduce the underlying mechanism. The result shows that the higher content of the fluorinated side-chain in polymer contribute to the lower surface energy and the higher pretilt angle. The atomic ratio of fluorine is largely decreased by ion beam treatments. The alignment uniformity and stability of the surfaces treated by linearly-polarized UV light and ion beam bombardment are also demonstrated.

Orientating layers with adjustable pretilt angles for liquid crystals deposited by a linear atmospheric pressure plasma source

A method for controlling the pretilt angles of liquid crystals (LC) was developed. Hexamethyldisiloxane polymer films were first deposited on indium tin oxide coated glass plates using a linear atmospheric pressure plasma source. The films were subsequently treated with the rubbing method for LC alignment. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy measurements were used to characterize the film composition, which could be varied to control the surface energy by adjusting the monomer feed rate and input power. The results of LC alignment experiments showed that the pretilt angle continuously increased from 0° to 90° with decreasing film surface energy.

Medical displays by using plasma‐beam‐alignment technology

— Novel anode layer plasma within minimum chamber space was developed for non-contact alignment process. The plasma-treated polyimide (PI) surface showed no particle contamination and no micro-scratches. Surface morphology was investigated by using scanning electron microscope (SEM), an atomic force microscope (AFM), and X-ray photoemission spectroscopy. The different oxygen-to-carbon ratio ([O]/[C] ratio) for XPS spectra indicated a composition change after plasma treatment. Surface pretilt angles were varied from 0 to 2.1° under different plasma exposure times. Finally, a prototype 20.8-in. QXGA IPS-mode gray-scale medical liquid-crystal display was successfully demonstrated with high contrast ratio, excellent uniformity, and wide viewing angle using this new plasma-beam-alignment technique.

Plasma beam alignment of liquid crystal with improved alignment stability [LCD manufacture]

A method of plasma beam treatment providing liquid crystal (LC) aligning substrates of improved alignment stability is described. In this method the aligning substrates are obliquely treated with a plasma flux containing alignment and passivation agents simultaneously. This method is applicable for the substrates of organic and inorganic origin. During this treating process, good pretilt angle stability and alignment quality are much promised.

Design and synthesis of ferroelectric liquid crystals

New chiral organic acid 1 and alcohol 2 synthesized from natural lactate and (S)-1-iodo-2- meyhylbutane were used as chiral block for preparing ferroelectric liquid crystals. Six series of chiral liquid crystals were synthesized to study the molecular structure-liquid crystal phase relationship. Different liquid crystal phase sequence K-Sc*-SA-I, K-Sc*-N*-I, or K-N*-I is formed among them. The thermal stability of Sc* phases observed is high. These new FLCs and their mixtures could be useful for practical use. The results also indicate that compounds 1 and 2 could be helpful for preparing new FLCs.