Pretilt Angle Of Nematic Liquid Crystal Research Articles

GRADIENT ALIGNMENT MATERIALS WITH DIFFERENT PHOTOSENSITIVITY FOR TUNABLE POLARIZATION-INDEPENDENT LIQUID CRYSTAL LENS

The development of electrically tunable liquid crystal (LC) lenses is perspective and promising for a wide range of applications, for example, for imaging system, pico projectors, optical zoom systems, ophthalmology applications and other. Of particular note is the development of polarization-independent LC lenses, as eliminates polarizers from application devices that reduce the efficiency of light transmission through optical systems. Alignment benzaldehyde photosensitive materials, capable of changing the pretilt angles of nematic LC from 90 to 0 ºС in a controlled manner under UV exposure are developed. The anisotropy of the benzaldehyde alignment layers is generated by a two-stage treatment consisting of uniform rubbing with a cloth and subsequent non-polarized UV exposure. Inhomogeneous UV exposure of uniformly rubbed alignment layers allows formation of refractive index gradient inside the LC cell. The concept of tunable polarization-independent self-aligned LC lens based on gradient pretilt angle alignment materials with different photosensitivity is demonstrated. Self-alignment of two polarization-dependent sub-lens is achieved due to a single UV exposure act of two alignment layers, which are located on the same piece of glass on both sides, forming one common optical axis for a polarization-independent LC lens. The independence of the polarization of LC lenses is achieved by setting the azimuthal rubbing direction of the alignment layers of two polarizationdependent LC lenses perpendicular to each other. The sub-lens cells have uniform cell gap and are independently controlled using low-voltage driving. Devices based on gradient benzaldehyde alignment materials can be used in many modern optical and photonic devices.

Photo alignment Behaviors of Photopolymer with Cinnamate Group by LPUV Method

The side chain photopolymer containing terminally substituted methoxy cinnamoyl ester was synthesized and characterized. The para position in the methoxy cinnamoyl group was connected with polymer backbone through 4 numbers of methylene spacer. A good thermal stability of photopolymer was measured by thermogravimatric analysis (TGA) measurement until 400 ℃ while the glass transition temperature was observed that high PMC according to the results of differential scanning calorimetry (DSC). The nematic liquid crystal (NLC) pretilt angle generated was about 0.06-1.66 by polarized different UV exposure energy. Especially, the low pretilt angle of the NLC was measured by the longer polarized UV exposure time. This result indicated that the NLC pretilt angle generated sensitively depends on the UV exposure time on the photopolymer layer.

Polarization-Dependence of Liquid Crystal Alignment on an Organic Insulation Thin Film with Ion Beam Irradiation Explained by Brewster's Law

We used Brewster's Law to examine the mechanism of liquid crystal (LC) alignment on an organic insulation layer when subjected to ion-beam irradiation. Brewster's Law implies that the maximum rate polarized ray on a slanted insulation layers on the substrate and it illustrates the dependence of polarization and the mechanical structure on the ion beam irradiation process. The pretilt angle of nematic LCs on the organic insulation surface was about 1.13° for an ion beam exposure of 45° for 1 minute at 1800 eV. This shows the dependence of LC alignment on the polarization ratio in a slanted organic insulation layer. We also discussed the electro-optical characteristic of twisted nematic (TN) LCD using ion beam irradiation on organic overcoat layer.

Homeotropic Alignment of Nematic Liquid Crystals by a Photocross-Linkable Organic Monomer Containing Dual Photofunctional Groups

In this paper, we report a novel organic monomer containing dual photocross-linkable groups and success in realizing photoinduced homeotropic alignment of nematic liquid crystals (LCs) with it. It was first revealed that direct irradiation of the photoalignment thin film with nonpolarized ultraviolet (UV) light at 365.0 nm brought out homeotropic orientation of the photopolymer as a result of the photocross-linking of the dual photoreactive groups. When the thin film was obliquely irradiated with nonpolarized UV light, the pretilt angles of nematic LC were generated. Interestingly, we find that the hydrophobicity of the photopolymer increases with increasing irradiation time. In discussing the mechanism of the homeotropic alignment, it was found that the incorporation of the dual photofunctional group of the photoalignment molecules as well as the extreme hydrophobicity of the photopolymer play the essential roles. This monomer cross-linked film is expected as a promising homeotropic alignment film with rubbing-free processing for the fabrication of advanced vertical alignment LC displays.

Annealing Behavior of Pretilt Angles on Polyimide Surface with Rubbing and Ion Beam Irradiation

We have studied the liquid crystal (LC) alignment, the pretilt angle generation, and the annealing behavior for a nematic liquid crystal (NLC) on the homogeneous polyimide (PI) surfaces by using the rubbing method and the ion beam (IB) method. An excellent LC alignment of the NLC on the PI surface with rubbing and IB irradiation were observed. The pretilt angle of NLC on the homogeneous PI surface for the rubbing method is decreased from to as rubbing time is increased, that of the for the IB irradiation method is decreased from to as the time of IB irradiation is increased. After the annealing, the pretilt angles of the rubbed PI surfaces increased up to , these of the IB irradiated PI surfaces little increased. It is considered the side chain of the rubbed PI show the its abilities of the original capacities, while the side chain of the IB irradiated PI cannot show the its abilities of the original capacities due to the IB has already destroyed the side chain of the PI.

Liquid Crystal Alignment Effects on Nitrogen-doped Diamond like Carbon Layer by Ion Beam Alignment Method

We have studied the nematic liquid crystal (NLC) alignment effects on a nitrogen-doped diamond-like carbon (NDLC) thin film layer with ion beam irradiation. The pretilt angle for NLC on the NDLC surface with ion beam exposure was observed below 1 degree. Also, we had the good LC alignment characteristics on the NDLC thin films with ion beam exposure of 1800 eV. In thermal stability experiments, the alignment defect of the NLC on the NDLC surface with ion beam irradiation above annealing temperature of can be observed. Therefore, the good thermal stability and LC alignment for NLC by ion beam aligned NDLC thin films can be achieved.

Effect of para-substituents of azobenzene side chains tethered to poly(methacrylate)s on pretilt angle photocontrol of nematic liquid crystals

In this paper, we describe the effect of para-substituents of azobenzene side chains attached to poly(methacrylate)s on both photoinduced dichroism of the polymer films and pretilt angle photocontrol of nematic liquid crystals (LCs). Oblique exposure of the polymer films to non-polarized light gave rise to azimuthal photodichroism in parallel with the incident plane of actinic light. The photodichroism behavior was markedly influenced by the para-substituents of azobenzenes. Ellipsometric measurement revealed that the azobenzene moieties were inclined in optically biaxial manner probably because the polymer matrix is probably anchored at the substrate surface. When the cells were fabricated with nematic LCs, the polymer films generated homeotropic LC orientation, which was continuously transformed into homogeneous and even tilted alignment by oblique exposure to non-polarized 436 nm light. On the other hand, the transient pretilt angles of LCs were not measurable by oblique exposure to non-polarized 365 nm light though the tilted LC orientation was obtained at the photostationary state. This happened from the deterioration of LC orientation that takes place from the E-to- Z photoisomerization of azobenzenes at the outmost polymer surfaces. The photoinduced pretilt angles of nematic LCs were distinctly governed by the molecular structures of the azobenzene-containing polymers.

Characterization and Alignment Properties on Polyimide Surface Using Polymer Films for Flexible Liquid Crystal Displays

We have investigated the generation of pretilt angle for nematic liquid crystal (NLC) alignment by the rubbing alignment method in two types of polyimide (PI) surfaces using polymer substrates. The NLC pretilt angle generated by the rubbing alignment method on a polymer substrate is about 3 deg, and it tends to decrease as rubbing strength increases. The pretilt angle measured is about 1.7 deg smaller on the glass substrate than on the polymer substrate. We obtain an atomic force microscope (AFM) image of the rubbed PI surface with a polymer film that has formed the micro-groove structure at a low curing temperature (120°C). However, no grooves were obtained on the glass substrate at the same temperature. It is considered that this alignment may be attributed to the roughness of the micro-groove substrate. Therefore, LC alignment is affected by the type of topographical structure. The pretilt angle was larger on the rubbed soluble-type PI surface with a higher imidization rate using the polymer film; the pretilt angle on the polyimide surface is attributed to high imidization rate of the PI. Consequently, flexible LCDs required at the low-temperature processing should use the soluble-type PI as the alignment layer. Also, good eletrooptical (EO) curves were observed for the TN-LCD using the polymer substrate at a low curing temperature.

Photogeneration of High Pretilt Angles of Nematic Liquid Crystals by Non‐Polarized Light Irradiation of Azobenzene‐Containing Polymer Films

AbstractA vertical‐alignment (VA) cell of nematic liquid crystals (LCs) was prepared using photoirradiated thin films of a poly(methacrylate) with mesogenic moieties of 4‐trifluoromethoxyazobenzene as the side chains. Optical anisotropy was generated by oblique irradiation of the azobenzene‐containing polymer films with non‐polarized UV light, followed by annealing treatment to enhance the photodichroism, which displayed thermal stability. The combination of oblique exposure to non‐polarized UV light and subsequent annealing treatment brought about high pretilt angles of nematic LCs so that a photoaligned VA LC cell was fabricated. The photopatterned LC cell exhibited electro‐optical properties with excellent optical quality when a voltage was applied even after heating at 100 °C for several hours.

Control of High Pretilt Angle in NLC, 5CB, by the Washing Process on a Polyimide Surface with CF3 Moieties

The washing effects on pretilt angle generation in a nematic liquid crystal (NLC), 4-n-pentyl-4′-cyanobiphenyl (5CB) on a rubbed polyimide (PI) surface with trifluoromethyl moiety have been successfully studied. The pretilt angle of 5CB is increased by the washing process on the rubbed PI surface. The surface tension on the rubbed PI surface increases with the rubbing strength RS and then saturated above RS = 150 mm. The pretilt angle of 5CB for all washing processes on the rubbed PI surface decreases with the surface tension. We have found that the pretilt angle of 5CB on the rubbed PI surface may be attributed van der walls (VDW) dispersion interaction between the LC molecules. and the polymer surfaces having trifluoromethyl moieties.

Washing Effects on Generation of Pretilt Angle in NLC, 5CB, on a Polyimide Surface with Trifluoromethyl Moieties

The washing effects on pretilt angle generation in a nematic liquid crystal (NLC), 4-n-pentyl-4'-cyanobiphenyl (5CB) on a rubbed polyimide (PI) surface with trifluoromethyl moiety have been successfully studied. The pretilt angle of 5CB is increased by the washing process on the rubbed PI surface. The surface tension on the rubbed PI surface increases with the rubbing strength RS and then saturated above RS: 150 mm. The pretilt angle of 5CB for all washing processes on the rubbed PI surface decreases with the surface tension. We have found that the pretilt angle of 5CB on the rubbed PI surface may be attributed van der walls (VDW) dispersion interaction between the LC molecules and the polymer surfaces having trifluoromethyl moieties.

Aligning Capabilities of Nematic Liquid Crystal on Photopolymer-Based N-(phenyl)maleimide Homopolymers

The photoalignment material poly [4-fluorocinnamate (phenylmaleimide)] (PFCPMI), was synthesized and the nematic liquid crystal (NLC) alignment effects on the photopolymer surface were studied. The NLC pretilt angle generated using a UV filter-less method on the PFCPMI surface was higher than that of the UV filter method. A good LC alignment with the UV filter-less method was observed at an annealing temperature of 150°C, and the alignment defect of the NLC was observed above annealing temperature of 180°C. Consequently, a high NLC pretilt angle and the good thermal stability of LC alignment using the UV filter-less method on the photopolymer surface can be achieved.

Fluorine 계열의 폴리머를 함유한 복합 폴리이미드 표면에서의 네마틱 액정의 프리틸트 발생의 메카니즘

The mechanisms of pretilt angle generation for a nematic liquid crystal (NLC) with negative dielectric anisotropy on the blended polyimide (PI) surface containing trifluoromethyl moiety were studied. High LC pretilt angle on the blended polymer surface with F3 was measured and the pretilt angle increased with rubbing strength. However, the low LC pretilt angle on the blended polymer surface with F1 and F2 was measured. The high LC pretilt angle generated is attributable to trifluoromethyl moiety in backbone structure on the blended PI surface. Therefore, the high pretilt angle of NLC can be achieved by using the blended polymer surface.

Diamond-like Carbon 박막을 이용한 액정 배향 효과

We studied the nematic liquid crystal (NLC) aligning capabilities using the new alignment material of a diamond like carbon (DLC) thin film. A high pretilt angle of about <TEX>$3.5^{\circ}$</TEX> by ion beam(IB) exposure on the DLC thin film surface was measured. A good LC alignment by the IB alignment method on the DLC thin film surface was observed at annealing temperature of <TEX>$200^{\circ}C$</TEX>, and the alignment defect of the NLC was observed above annealing temperature of <TEX>$220^{\circ}C$</TEX>. Consequently, the high NLC pretilt angle and the good thermal stability of LC alignment by the IB alignment method on the DLC thin film surface can be achieved.

Liquid Crystal Alignment Effects on the Photo-Crosslinkable Copolymer Surfaces Containing Cholesteryl Moiety

Pretilt angle generation for a nematic liquid crystal (NLC) and electro-optical (EO) performances of the vertical-alignment (VA)-liquid crystal display (LCD) photoaligned with obliquely polarized UV exposure on the three kinds of copoly (M4Ch-ChMA), copoly ((4-methacryloyloxy) chalcone - cholesteryl methacrylate) surfaces for homeotropic LC alignment were studied. The NLC pretilt angle of 81° was observed with UV exposure of 3 min on the photo-crosslinkable copolymer surface. The NLCs pretilt angle is attributable to increased chalcone with increasing the UV exposure time. Also, a good voltage-transmittance (V-T) curve and fast response time in the VA-LCD photoaligned with obliquely polarized UV exposure of 30 ° on the photo-crosslinkable copolymer surfaces can be achieved.

Liquid Crystal Alignment Effects on the Photo-Crosslinkable Copolymer Surfaces Containing Cholesteryl Moiety

Pretilt angle generation for a nematic liquid crystal (NLC) and electro-optical (EO) performances of the vertical-alignment (VA)-liquid crystal display (LCD) photoaligned with obliquely polarized UV exposure on the three kinds of copoly (M4Ch-ChMA), copoly ((4-methacryloyloxy) chalcone - cholesteryl methacrylate) surfaces for homeotropic LC alignment were studied. The NLC pretilt angle of 81° was observed with UV exposure of 3 min on the photo-crosslinkable copolymer surface. The NLCs pretilt angle is attributable to increased chalcone with increasing the UV exposure time. Also, a good voltage-transmittance (V-T) curve and fast response time in the VA-LCD photoaligned with obliquely polarized UV exposure of 30 ° on the photo-crosslinkable copolymer surfaces can be achieved.

Investigation of Liquid Crystal Alignment and Pretilt Angle Generation in the Cell with Linearly Polarized UV Light Irradiation on Polymer Surface

We have investigated the generation of pretilt angle in nematic liquid crystal (NLC) and electro-optical (EO) characteristics of photo-aligned TN-LCD with polarized ultraviolet (UV) light irradiated on polyimide (PI) surface. It was found that the LC alignment capability increases with increasing the UV light irradiation time. In case of the fact that the polarized UV light of oblique angle of 60° irradiated on PI surface rotated by 90° at 10 min. after being normally irradiated on PI surface at 30 min., the generated pretilt angle of NLC is about 1.5°. Also, we obtained that the pretilt angle in NLC strongly depends on oblique angle and UV light irradiation time. We considered that the pretilt angle of NLC is attributed to the interaction between the LC molecules and the polymer surface due to photo-depolymerization of polymer. Finally, we measured that the EO characteristics of photo-aligned TN-LCD is almost same in comparison to rubbing-aligned TN-LCD.

Generation of pretilt angle in NLCs and EO characteristics of a photo-aligned TN-LCD with oblique non-polarized UV light irradiation on a polyimide surface

We have investigated the generation of pretilt angle for a nematic liquid crystal (NLC) alignment in cells with oblique non-polarized ultraviolet (UV) light irradiation on polyimide (PI) surfaces. It was found that monodomain alignment of the NLC is obtained with an incident angle of 70 degrees and 75 degrees on the PI surface. It is considered that this alignment may be attributed to the anisotropic dispersion force due to photo-depolymerization of polymer on PI surfaces. Also, the generated NLC pretilt angles are all about 3 degrees at an incident angle of 70 degrees and 75 degrees for 1 h irradiation. Next, we observed that the voltage-transmittance characteristics for a photo-aligned twisted nematic (TN) LCD with an incident angle of 80 degrees on a PI surface were excellent. Also, we measured that the voltage-holding-ratio (VHR) of a photo-aligned TN-LCD is about 94%; it is almost same as obtained for rubbing-aligned TN-LCDs. Finally, the slow response time of photo-aligned TN-LCDs is attributable to their weak anchoring strength.

Generation of pretilt angle in NLC and EO characteristics of transcription-aligned TN-LCD fabricated by transcription alignment on polyimide surfaces

In this work, we have investigated the monodomain alignment of a nematic liquid crystal (NLC) in cells fabricated by transcription alignment on a polyimide (PI) surface with side chain. The generated pretilt angle of the NLC is about 3.7degree; it decreases with increasing rubbing time of the original substrate. It is considered that the generation of the pretilt angle in a NLC may be attributed to steric interaction of the polymer side chain. It is also suggested that LC alignment produced by transcription alignment techniques is attributable to the memory effect of the NLC on the PI surface. We also observed good voltage-transmittance characteristics for a transcription-aligned twisted nematic (TN-LCD) on a PI surface; it is almost the same as for a rubbing-aligned TN-LCD. Finally, we suggest that the slow response time characteristics of a transcription-aligned TN-LCD may be attributed to the weak anchoring strength of the NLC.

Preliminary communication Generation of high pretilt angle in a nematic liquid crystal with single oblique polarized UV light irradiation on polyimide surfaces

We propose and investigate obtaining high pretilt nematic alignment using a new photoalignment method: single oblique polarized ultraviolet (UV) light irradiation on polyimide (PI) surfaces. It was found that the monodomain alignment in a nematic liquid crystal (NLC) is obtained with PI surfaces having side chains. We successfully observed that the generated high pretilt angles of the NLC are about 6 with an angle of incidence of 5 80 on the PI surface. Also, the generated pretilt angle of NLC is about 6 with an UV light irradiation of 30 min for angle of incidence of 5, and decreases with increasing UV light irradiation time. High pretilt orientation of the NLC is successfully observed in cells with a single oblique UV light irradiation on PI surfaces.