Liquid Crystal Alignment Capability Research Articles

Liquid crystal aligning capabilities on surface-reformed indium-doped zinc oxide films via ion-beam exposure

ABSTRACTWe investigated the characteristics of a solution-processed indium-doped zinc oxide (In:ZnO) film formed via ion-beam (IB) irradiation as a liquid crystal (LC) alignment layer. The In:ZnO film was deposited using solution processing and cured at various temperatures. Uniform LC alignment was observed at all curing temperatures in cross-polarised optical microscopy images. A regular pre-tilt angle supported these results and showed homogeneous LC alignment. Several surface analyses were conducted to evaluate the effect of IB irradiation on the In:ZnO film surface. X-ray diffraction analysis showed an amorphous structure both before and after IB irradiation, and physical surface reformation was observed using atomic force microscopy. Root mean square surface roughness was reduced and a smooth surface was achieved after IB irradiation. X-ray photoelectron spectroscopy was used to detect chemical surface reformation. It was found that the IB irradiation broke the metal-oxide bonds and increased the occurrence of oxygen vacancies, which affected the van der Waals forces between the LC molecules and the In:ZnO film surface. Electrical performance was observed to identify the possibility of using the In:ZnO film in LC applications. Enhanced electro-optical performance was measured and zero residual DC voltage which was verified using a capacitance-voltage curve was achieved.

Alignment of Liquid Crystals Using a Molecular Layer with Patterned Molecular Density

The surface of self-constructed molecular density modulation (SDM) exhibits a wide range of liquid crystal alignment capabilities including planar, tilted, and homeotropic alignments, disclination-free uniform and heterogeneous alignments, and even spatially varying alignments through the single non-contact process. Alignment defects are eliminated by temporary lowering the frictional energy barrier via the open-boundary elastic stabilization (OES) treatment.

Homogeneously Aligned Liquid Crystals on a ZrO2 Alignment Film Using Ion-Beam Irradiation

This paper introduces the characteristics of the zirconium dioxide (ZrO2) inorganic film deposited by radio-frequency magnetron sputtering. The homogeneously aligned liquid crystal (LC) on ZrO2 layer via ion beam (IB) irradiation at various incident angles was embodied with LC alignment capability and performance. The x-ray photoelectron spectroscopic (XPS) data shows that O-Zr bonds on the ZrO2 surface are broken and induce the van der Waals force for the homogeneous alignment of LCs. That is the van der Waals force, affecting the alignment of the LCs, is verified by the contact angle of the liquid and by the XPS analysis on the ZrO2 thin film. In addition, the advantage of IB alignment method is verified by using atomic force microscope (AFM).

Liquid crystal alignment on a ZrO2 thin film as a function of ion beam incident angle

Nematic liquid crystal alignment capabilities and electro-optical performance characteristics have first been embodied in a ZrO2 layer using ion-beam irradiation. The study demonstrates that liquid crystal layers can be aligned homogeneously as a function of the incident angle of the ion beam device, which causes a uniform dense plasma. X-ray photoelectron spectroscopy indicated that full oxidation of the ZrO2 thin-film surfaces was produced by ion irradiation, shifting the Zr 3d spectra to lower binding energies. In addition, the electro-optical performance characteristics of twisted nematic cells on a ZrO2 thin-film layer after ion beam irradiation showed similar characteristics to those of a rubbed polyimide cell.

Liquid Crystal Alignment Capabilities on SiNx Thin Films Via Ion-Beam Irradiation

The aligned liquid crystals (LCs) display on SiNx thin films using ion-beam (IB) irradiation was studied with controllability of pretilt angle depending on incident energies of the IB. The LCs alignment property for the SiNx thin films were observed to verify the practical application potential. A good LCs alignment of vertical alignment LCs cells on SiNx thin film surfaces irradiated with incident IB energy of 1800eV was achieved. The atomic force microscopy (AFM) images of LCs on SiNx thin film surfaces irradiated with IB energy was used for the surface analysis.

Liquid Crystal Alignment Capabilities on SiNx Thin Films Via Ion-Beam Irradiation

The aligned liquid crystals (LCs) display on SiNx thin films using ion-beam (IB) irradiation was studied with controllability of pretilt angle depending on incident energies of the IB. The LCs alignment property for the SiNx thin films were observed to verify the practical application potential. A good LCs alignment of vertical alignment LCs cells on SiNx thin film surfaces irradiated with incident IB energy of 1800 eV was achieved. The atomic force microscopy (AFM) images of LCs on SiNx thin film surfaces irradiated with IB energy was used for the surface analysis.

IPS mode investigation of liquid crystal alignment on organic hybrid overcoat layer via ion beam irradiation

The nematic liquid crystal alignment capability and electro‐optical (EO) performance characteristics of in‐plane switching (IPS) cells were first demonstrated on organic hybrid overcoat layers via ion beam irradiation. Usually the organic hybrid overcoat is used as the material for making a plate alignment layer in a colour filter process. To characterise the organic hybrid overcoat layer, we analysed the surface composition of the organic hybrid overcoat by X‐ray photoelectron spectroscopy. The results show that the intensity of C = O and C–O bonding undergoes a change corresponding to the changes in energy of the ion beam exposure. Moreover, EO performance characteristics of IPS cells on the organic hybrid overcoat layer via ion beam irradiation were observed to have similar characteristics to the polyimide.

Liquid Crystal Aligning Capabilities Treated on Organic Overcoat Thin Films by Ion Beam Irradiation Method

The liquid crystal display (LCD) applications treated on the organic overcoat thin film surfaces by ion beam irradiation was successfully studied. The good LC aligning capabilities treated on the organic overcoat thin film surfaces with ion beam exposure of for 2 min above ion beam energy of 1200 eV can be achieved. But, the alignment of defect of NLC on the organic overcoat surface at low energy of 600 eV was measured. The pretilt angle of NLC on the organic overcoat thin film surface with ion beam exposure of for 2 min at energy of 1800 eV was measured about 1 degree. Finally, the good thermal stability of LC alignment on the organic overcoat thin film surface with ion beam exposure of for 2 min until annealing temperature of can be measured.

Liquid Crystal Aligning Capabilities and EO Characteristics of the TN-LCD with Ion-Beam Exposure on a New Diamond-like Carbon Thin Film Layer

Liquid crystal (LC) alignment capabilities with ion beam (IB) exposure on a diamond like carbon (DLC) layer were studied. A high pretilt angle of 3.5° with IB exposure on the DLC layer can be obtained. Superior LC alignment with the IB alignment method on the DLC layer was observed until an annealing temperature of 200°C. Also, excellent voltage-transmittance (V-T) curve of the ion beam aligned twisted nematic (TN) cell with oblique ion beam exposure on the DLC surface for 1 min was observed. The fast response time of the ion beam aligned TN cell with oblique ion beam exposure on the DLC surface for 1 min can be achieved. The residual DC property of the ion beam aligned TN cell with ion beam exposure on the DLC layer for 1 min is almost same as that of the rubbing aligned TN cell on a rubbed polyimide (PI) surface.

Liquid Crystal Aligning Capabilities and EO characteristics of the Photoaligned TN-LCD on a Photo-crosslinkable Polyamides Based Polymer

In this work, synthesis of a photo-crosslinkable polyimide (polyimide (PI)-chalcone(Chal)-biphenyl (BP)) based polymer and electro-optical (EO) performances of photoaligned twisted nematic (TN) - liquid crystal displays (LCDs) using the two kinds of the photodimerization method with obliquely polarized UV exposure on a photopolymer were investigated. High pretilt angle of the NLC was measured by polarized UV exposure using the conventional photodimerization method on the PI-Chal-BP surface for 3 min. The high pretilt angle of the NLC generated in NLC is attributable to the biphenyl moieties and the photodimerized chalcone group of the photopolymer. The NLC pretilt angle using the conventional photodimerization method was higher than that of a in-situ photodimerization method. Additionally, good voltage-transmittance (V-T) curves and response time for the photoaligned TN-LCD were observed by UV exposure on the PI-Chal-BP surface for 3 min using conventional photodimerization method. However, EO characteristics of the photoaligned TN-LCD on the PI-Chal-BP surface for 1 min using the in-situ photodimerization method were achieved.

Liquid Crystal Aligning Capabilities on New Photo-Crosslinkable Polyimide Based Polymer by the Photodimerization Method

Liquid Crystal Aligning Capabilities on New Photo-Crosslinkable Polyimide Based Polymer by the Photodimerization Method

Liquid Crystal Aligning Capabilities on New Photo-Crosslinkable Polyimide Based Polymer by the Photodimerization Method

We studied the liquid crystal (LC) alignment and pretilt angle generation for a nematic (N) LC using a photodimerization method on various new photo-crosslinkable polyimide based polymer. A good thermal stability of the photopolymers was measured by thermogravimatric analysis (TGA) measurement until 450°C. High pretilt angle of the NLC was obtained by polarized UV exposure on the photopolymers containing biphenyl (BP), decyl (de), and cholesteryl (chal) group, respectively. However, low pretilt angle of the NLC was measured by polarized UV exposure on the photopolymers containing fluorine and chalcone group. The high NLC pretilt angle generated is attributable to the biphenyl, alkyl moieties, and photodimerized chalcone group of the photopolymer. Also, a good the electro-optical (EO) characteristics in the TN-LCD photoaligned with UV exposure of 30θ on the photopolymer surface can be achieved.

Liquid crystal alignment capabilities on rubbed organic solvent soluble polyimide surfaces with trifluoromethyl moieties

High pretilt angles, polar anchoring energy (out of plane-tilt), and surface ordering in the nematic liquid crystal 4-n-pentyl-4'-cyanobiphenyl (5CB) were investigated on rubbed organic solvent soluble polyimide (PI) surfaces with a helical backbone structure and trifluoromethyl moieties. It was found that the pretilt angle of 5CB is about 15° in the wide rubbing region of rubbed soluble PI surfaces with trifluoromethyl moieties attached to the lateral benzene rings. It is suggested that the microscopic surface structure of the polymer contributes to the LC pretilt angle generation at the surface. Also, the polar anchoring energy of 5CB is dependent on the molecular structure of these unidirectionally rubbed soluble PI surfaces. The polar anchoring strength of 5CB on rubbed soluble PI surfaces is as weak with trifluoromethyl moieties attached to the lateral benzene rings weak as when the trifluoromethyl moieties are attached to the polymer backbone. Finally, the polar anchoring energy of 5CB strongly depends on the surface ordering of rubbed soluble PI surfaces.

Liquid Crystal Alignment Capability on Polyimide Langmuir-Blodgett Surfaces with Alkyl Chain Lengths

The liquid crystal (LC) alignment capability in 4-n-pentyl-4′-cyanobiphenyl (5CB) on polyimide (PI) Langmuir-Blodgett (LB) surface with alkyl chain lengths was investigated. The pretilt angle of 5CB increased by unidirectional rubbing treatment on PI-LB surface. The induced optical retardation on PI-LB surface increased by the rubbing. The extrapolation length de of 5CB for rubbed PI-LB surfaces with even-number is small, compared with odd-number near the clearing temperature Tc. The extrapolation length de of 5CB with odd-number increases gradually as the temperature increases but it tends to diverge near the Tc. Therefore the polar anchoring strength with even-number is strong because of relatively high surface ordering caused by more crystalline surfaces. The anchoring energy of 5CB with alkyl chain length of 7 carbons is approximately 1 × 10−3 (J/m2); it indicates the strong anchoring strength. In consequence, we suggest that the LC aligng capability in NLC on PI-LB surface is strongly related to the characteristics of the polymer.

Surface Morphology of the Rubbed Polyimide and Polystyrene Films and Their Liquid Crystal Aligning Capability

Abstract Atomic force microscope (AFM) observation has been made on rubbed polymer films for liquid crystal (LC) molecular orientation such as those of alkylbranched and branchless polyimide (PI) together with polystyrene (PS); other characterizations such as Fourier analysis and roughness evaluation have also been made. It has been investigated how these results of the characterization relate to the LC aligning capabilities such as microscopic texture and pretilt angle. It is shown that in a PI film with alkylbranches there exist grooves owing to strong rubbing, while the branchless does not reveal grooves at the AFM resolution. However, both of them are shown to be capable of aligning nematic (N) LCs very well. Regarding PS film, the grooves run parallel to the rubbing direction but LC alignment is perpendicular to that of rubbing, in accordance with the previous report (D.-S. Seo et al., Jpn. J. Appl. Phys. 31, 2165C 1992)).