Liquid Crystal Alignment Films Research Articles

Temperature-switched orientation properties through physicochemically constructed aluminum zirconium oxide films

In general, it has one of the characteristics of homeotropic alignment and homogeneous alignment depending on the material and manufacturing process of the liquid crystal alignment layer. However, in this study, we propose a new type of alignment film that has the characteristics of changing the liquid crystal alignment direction according to the curing temperature. The AlZrO alignment film produced by the solution process and brush coating method showed homeotropic alignment characteristics when cured at low temperatures and homogeneous alignment characteristics when cured at high temperatures. These switching characteristics according to the curing temperature showed stable LC alignment, respectively, and the threshold voltages were 0.81 V and 0.857 V in vertical alignment (VA) mode and twisted nematic (TN) mode, respectively, demonstrating excellent electro-optical properties. The mechanism of these switching characteristics was analyzed through surface modification analysis. This study introduces new insights into liquid crystal alignment films that satisfy all of the high-efficiency fabrication process, various application possibilities due to their switching properties, and excellent electro-optical properties.

Ternary copolymerization photosensitive polyimide containing flexible group for liquid crystal alignment film

Ternary copolymerization photosensitive polyimide containing flexible group for liquid crystal alignment film

Physical Properties of Thermally Crosslinked Fluorinated Polyimide and Its Application to a Liquid Crystal Alignment Layer.

This study demonstrated the use of a thermally crosslinked polyimide (PI) for the liquid crystal (LC) alignment layer of an LC display (LCD) cell. Polyamic acid was prepared using 4,4′-oxydianiline (ODA) and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA). The 6FDA−ODA-based polyimide (PI) prepared by the thermal cyclic dehydration of the polyamic acid (PAA) was soluble in various polar solvents. After forming a thin film by mixing trifunctional epoxide [4-(oxiran-2-ylmethoxy)-N,N-bis(oxiran-2-ylmethyl)aniline] with the 6FDA−ODA-based PAA, it was confirmed that thermal curing at −110 °C caused an epoxy ring opening reaction, which could result in the formation of a networked polyimide not soluble in tetrahydrofuran. The crosslinked PI film showed a higher rigidity than the neat PI films, as measured by the elastic modulus. Furthermore, based on a dynamic mechanical analysis of the neat PI and crosslinked PI films, the glass transition temperatures (Tgs) were 217 and 339 °C, respectively, which provided further evidence of the formation of crosslinking by the addition of the epoxy reagent. After mechanical rubbing using these two PI films, an LC cell was fabricated using an anisotropic PI film as an LC alignment film. LC cells with crosslinked PI layers showed a high voltage holding ratio and low residual direct current voltage. This suggests that the crosslinked PI has good potential for use as an LC alignment layer material in advanced LCD technologies that require high performance and reliability.

Preparation of a novel ternary photosensitive polyimide for liquid crystal alignment films

ABSTRACT In order to obtain liquid crystal alignment films with better photosensitivity, transmittance and solubility, a ternary copolymer polyimide (BFB-PI-CA) is synthesised by benzophenone-3, 3′, 4, 4′-tetracarboxylic dianhydride (BTDA), 4,4ʹ-hexafluoroisopropyl phthalic anhydride (6FDA) and 2,2-bis (3-amino-4-hydroxyphenyl) propane (BAP). The initial thermal decomposition temperature (Td 5) of the BFB-PI-CA is 371°C. And it shows good solubility. The BFB-PI-CA film has excellent optical transparency in the visible region (400–700 nm) after UV irradiation, which transmittance at 400 nm is 95.3%. In addition, after irradiated by non-polarised ultraviolet light (NPUVL) for 15 min, the film can show excellent alignment performance which remains unchanged after 24 h at 100°C. The pretilt angle is 0.4°C, which can meet the use of liquid crystal display (LCD) in parallel mode.

Preparation and performance analysis of novel liquid crystal alignment films based on macromolecular photosensitiser and photosensitive polyimide

ABSTRACT A photosensitive polyimide (BF-CA) and a macromolecular photosensitiser (BB-CA) are successfully synthesised. The BF&BB-CA blend films based on BF-CA and BB-CA can induce uniform alignment of liquid crystal (LC) after the non-polarised ultraviolet light (NPUVL) exposure for 15 min. After exposure for the same time, LC alignment ability of the BF&BB-CA blend films is higher than that of BF-CA films and BB-CA films. The alignment performance of LC and pretilt angles induced by the BF&BB-CA films after treatment at 120°C for 4 h are nearly unchanged, indicating that the prepared films have excellent thermal stability. Furthermore, the pretilt angle of the LC cells is 0.5°, which can be used in In-Plane Switching mode LCD.

Effect of the functional diamine structure on the properties of a polyimide liquid crystal alignment film

A novel functional diamine containing triphenylamine moiety and biphenyl as well as a long alkyl chain, 4-dodecyloxy-biphenyl-4′,4′′-diaminotriphenylamine (DBDTA), was synthesized and characterized.

Flexible LCDs fabricated with a slit coater: Not requiring an alignment film

AbstractA homogeneously aligned liquid crystal layer on a substrate film on which it is not necessary to form a liquid crystal alignment film can be assembled by a slit coater. Types of twisted nematic and in‐plane switching flexible liquid crystal displays were demonstrated. The production time can be considerably shortened because of the lack of need for an alignment film. The slit coater method is also applicable to the roll‐to‐roll process.

Carrier Mobility Enhancement in Organic TFTs with Gate Insulator of Vertical Liquid Crystal Alignment Film

In order to improve the carrier mobility of pentacene organic thin-film transistors (O-TFTs), we have studied the effect of the gate insulator material on the mobility. In spite of a reduction of the grain size, a gate insulating polymer material with a low surface energy, which is used for vertical alignment films for liquid crystals, significantly enhances the carrier mobility of the pentacene TFTs from ∼0.4 to up to ∼1.2 cm2 Vs.

Dependence of Kind of Solvents for Washing on Surface of Rubbed Polyimide Film

We report effects of washing rubbed polyimide film on the near surface. Especially we focused dependence of solvent. Rubbed polyimide films have been used as liquid crystal alignment films in Liquid crystal displays (LCDs), and in actual LCD panel fabrication washing on film surfaces after rubbing is essential process to remove dust and pollution. We investigated the effects of washing by grazing incidence X-ray diffraction (GIXD) measurements. In GIXD, the X-ray penetration into the polymer was changed from 8 nm (suface sensitive) to 4 nm (bulk sensitive) by variation of the X-ray incidence angle. It was found that crystallization near the surface induced by soaking was considerably dependent on solvent. However, in-plane distribution of the surface polymer chains of polyimide film was not found to be dependent on the solvents.

Effects of Rubbing Condition and Soaking Time on Surface Crystallization of Rubbed Polyimide Film by Soaking into Acetone

Rubbed polyimide films have been widely used as liquid crystal alignment films for liquid crystal displays. Washing after rubbing is essential to fabricate liquid crystal displays, and should affect alignment of liquid crystal as well as rubbing. We investigated the effects of rubbing condition and soaking in acetone on polyimide films by grazing incidence X-ray diffraction. It was found that soaking in acetone promoted crystallization of surface aligned polymers, and that the crystallization by acetone was dependent on the initial polymer alignment. The larger initial crystalline phase was, the more newly crystallization occurred by soaking. It was also revealed that the crystallization by soaking in acetone was completed within 1min.

Molecular orientation in Langmuir–Blodgett films of polyfumarates carrying isopropylester and isopropylamide side chains

Molecular orientation in Langmuir–Blodgett (LB) films of poly(diisopropyl fumarate) (PDiPF) and poly(isopropyl N-isopropyl fumaramate) (PiPFAE), prepared by solution polymerization and emulsifier-free emulsion polymerization, respectively, was investigated. The π– A isotherms of both polymers indicated formation of stable Langmuir monolayers. The refractive index measurements as well as the polarized IR and UV spectroscopy of the LB films revealed that the backbones of the polymers were oriented parallel to the dipping direction of the substrate. The LB films were applied to a nematic liquid crystal alignment film, and the relationship between optical axes of the LB films and the alignment direction of the liquid crystal molecules was characterized. Utilization of PDiPF and PiPFAE as a matrix polymer for polymer dispersed liquid crystals was also examined, and a higher performance with a better contrast ratio was obtained for PiPFAE.

Effect of Rubbing on Polymers for Liquid Crystal Alignment Film Studied by Grazing-Incidence X-ray Diffraction and Reflection Ellipsometry

Rubbed polyimide films have been widely used as liquid crystal alignment films for liquid crystal displays (LCDs). We investigated the effect of rubbing on the surface molecules of polyimide films by using grazing incidence X-ray diffraction (GIXD) and reflection ellipsometry. We found that rubbing not only caused the polymer chains to align in the direction of rubbing but also to elongate near the film surface. However, the in-plane distribution of surface polymer chains of polyimide film was not found to be dependent on the rubbing conditions.

Design of polyimides for liquid crystal alignment films

Recent developments in the chemistry of polyimides (PIs) for liquid crystal (LC) alignment films are reviewed. Some important properties, such as low temperature curing, generation of pretilt angles, and electrical properties, are summarized with respect to the chemical structures of the PI materials. In addition, the future prospect of alignment films for enhanced LC display is also described. Copyright © 2000 John Wiley & Sons, Ltd.

Design of polyimides for liquid crystal alignment films

Recent developments in the chemistry of polyimides (PIs) for liquid crystal (LC) alignment films are reviewed. Some important properties, such as low temperature curing, generation of pretilt angles, and electrical properties, are summarized with respect to the chemical structures of the PI materials. In addition, the future prospect of alignment films for enhanced LC display is also described. Copyright © 2000 John Wiley & Sons, Ltd.

Liquid Crystal Alignment Film with Mixture of Polyimide and Side Chain LC by Langmuir-Blodgett Technique

The mixed films of poly(amic acid) and a side-chain liquid crystal, 11-[(4-cyano-4′-biphenyl) oxy] undecanyl vinyl ether(CN-11-M) were investigated as a LC alignment film to control the pretilt angle of a nematic LC. The mixed films were fabricated by the Langmuir-Blodgett technique. A stable monolayer of poly (amic acid) alkylamine salt(PAAS) and CN-11-M was formed at the air-water interface. A Y-type film on 1TO glass was established at 25 mN/m and room temperature and was confirmed by FTIR spectroscopy. The number of layer was 4, and the ratio of PAAS and CN-11-M was varied. Surface tensions of these films were observed by measuring the contact angle of test liquid. Antiparallel cells were made to measure the pretilt angle of LC by crystal rotation method. Polar force in the mixed film increased with the amount of CN-11-M, but showed a maximum. The pretilt angles of nematic liquid crystal also showed the maximum at a fixed ratio of PAA and CN-11-M.

Characteristics of polyimide liquid crystal alignment films for active matrix-lcd use.

Synthesis, characterization, and liquid crystal (LC) aligning capability of polyimide (PI) for the active matrix (AM) liquid crystal display (LCD) application are demonstrated and discussed. The synthesized PI materials in this research are featured by: 1) a low curing temperature below 200°C due to their organic-solvent-soluble property; 2) a good unidirectional LC alignment; 3) a useful capability for generating desired pretilt angles; and 4) an excellent voltage holding ratio. The methods and mechanisms of the unidirectional LC alignment, the generation of pretilt angle, and voltage holding ratio are discussed.

Development, Characterization, and Characteristics of Polyimide Liquid Crystal Alignment Films for AM-LCD Use

Development, Characterization, and Characteristics of Polyimide Liquid Crystal Alignment Films for AM-LCD Use

Polyamide-Type High Pretilt Surface: Effect of Side-Chain Structure and Type of Liquid Crystals on the Generation of Pretilt Angle

Abstract Highly N-aralkylated poly(p-phenylene terephthalamide) (PPTA) with various substituents having benzyl units in their structures were synthesized in a high yield, and their properties as a liquid crystal alignment film were studied. Good liquid crystal alignment and pretilt angles of 0.5 to 8.1 deg were observed on the spin-coated polymer films after rubbing when a nematic liquid crystal, ZLI-2293 was used. The induced pretilt angle showed no correlation with the surface-free energy of the polymer film, but was strongly dependent on the structure of the side chain. The effects of the structural difference of the side chain and type of liquid crystals are discussed in more detail.

Liquid crystal alignment films produced by the R.F. Plasma beam technique

An rf plasma system is described suitable for deposition of anisotropic SiO(in2) films capable of aligning liquid crystal cells parallel to the substrate surface at approximately zero tilt and perpendicular to the plane of incidence. The electrooptical response of twisted cells made by this technique and their e(H) curves are discussed.