Liquid crystal photo-alignment layers made from aromatic bismaleimides

We propose a new type of liquid crystal photo-alignment layer made from aromatic bismaleimides. Aromatic bismaleimides are expected to react anisotropically by irradiation of polarized ultraviolet (UV) light. In the fabrication process of the new photo-alignment layers the curing process is much shorter than that needed for conventional polymeric types of photo-alignment layers. We have proved that the use of aromatic bismaleimides enables liquid crystal molecules to be aligned homogeneously by irradiation of polarized UV light. In particular N , N '- p -phenylenebismaleimide shows good photo-alignment characteristics and high UV sensitivity. In studying the relationship between molecular structures of aromatic bismaleimides and photo-alignment properties, we find that aromatic bismaleimides that have a linear molecular structure and resonance structure produce good photo-alignment layers.     

Liquid crystal photo-alignment layers made from aromatic bismaleimides

We propose a new type of liquid crystal photo-alignment layer made from aromatic bismaleimides. Aromatic bismaleimides are expected to react anisotropically by irradiation of polarized ultraviolet (UV) light. In the fabrication process of the new photo-alignment layers the curing process is much shorter than that needed for conventional polymeric types of photo-alignment layers. We have proved that the use of aromatic bismaleimides enables liquid crystal molecules to be aligned homogeneously by irradiation of polarized UV light. In particular N,N′-p-phenylenebismaleimide shows good photo-alignment characteristics and high UV sensitivity. In studying the relationship between molecular structures of aromatic bismaleimides and photo-alignment properties, we find that aromatic bismaleimides that have a linear molecular structure and resonance structure produce good photo-alignment layers.     

Photo-induced liquid crystal alignment on polyimide containing fluorinated groups

Polyimides were prepared from pyromellitic dianhydride, 4,4'-bis[2-(4-aminophenyl)hexafluoroprop-2-yl]diphenyl ether and 4,4'-diamodiphenyl ether (PMDA-BDAF-ODA) and used for liquid crystal alignment using linearly polarized UV exposure. The alignment properties of a LC on the polyimide films were found to depend on the fluorine content in the PMDA-BDAF-ODA alignment layer and on the UV exposure time. Pretilt angles were obtained in the range 0° to 90° dependent upon the fluorine content in the polyimide film and the UV exposure time. These effects seem to be closely related to the surface energy of the photo-alignment layer.     

一种带肉桂酸酯基的聚酰亚胺液晶光定向材料研究

利用双酚A二胺单体(BISDA)与4,4-′(六氟异丙基)-双邻苯二甲酸酐(6FDA)的缩聚反应,制备了含有侧羟基的先驱聚合物PI-OH.通过PI-OH与肉桂酰氯的官能化反应,得到接有肉桂酸酯感光侧基的双酚A型聚酰亚胺PI-CI.用红外光谱(FTIR)、氢核磁共振(1H-NMR)分析、热分析(DSC)等方法表征了上述聚合物的结构和热性能.利用紫外-可见光谱(UV-Vis)对PI-CI的感光性能进行了研究.在线偏振紫外光辐照下,上述聚合物膜表现出二色向性.二向色性的强弱随光照能量的变化存在最大值.经线性偏振紫外光(LPUV)辐射后的PI-CI薄膜能诱导液晶盒中液晶分子发生均匀的定向沿面排列.上述实验表明,该聚酰亚胺是一类具有优良性能的潜在液晶光定向材料.     

Pretilt angle generation by UV exposure during imidization of polyimide

We investigated pretilt angle generation and liquid crystal (LC) alignment by ultraviolet exposure during the imidization of polyimide (PI). The generated pretilt angle of a nematic (N) LC using an in situ photo-alignment method is smaller than that using a conventional photo-alignment method on a surface of PI having side chains. The NLC pretilt angles using an in situ photo-alignment method injected at isotropic phase increased with annealing were observed.     

Pretilt angle generation by UV exposure during imidization of polyimide

We investigated pretilt angle generation and liquid crystal (LC) alignment by ultraviolet exposure during the imidization of polyimide (PI). The generated pretilt angle of a nematic (N) LC using an in situ photo-alignment method is smaller than that using a conventional photo-alignment method on a surface of PI having side chains. The NLC pretilt angles using an in situ photo-alignment method injected at isotropic phase increased with annealing were observed.     

Photo-alignment of liquid crystals using a crosslinked discotic film

A new photo-alignment layer using a crosslinked discotic compound was demonstrated. This discotic compound exhibits excellent solubility in common organic solvents, the possibility of low temperature processing and good thermal stability. A linearly polarized long wavelength ultraviolet (LPUV) light (λ = 350 nm) was used to initiate the crosslinking process and induce liquid crystal alignment on the discotic film surface. The induced LC directors were found parallel to the electric field direction of the LPUV light. A 1.2° pre-tilt angle was achieved using a single exposure at a 30° oblique angle.     

Alignment of polymer network-stabilized ferroelectric liquid crystal using a magnetic field

Polymer network-stabilized ferroelectric liquid crystals with homogeneous alignment have been produced in cells without a surface alignment layer. In this technique, a crosslinkable monomer is mixed into a ferroelectric liquid crystal and polymerized in a magnetic field to form a polymer network that will stabilize the alignment of the ferroelectric liquid crystal. The concentration of the monomer is an important factor in achieving alignment of the ferroelectric liquid crystal. Both the morphology of the final composite layer and the molecular alignment of the host FLC are affected by the curing temperature at which the UV curing of the sample is started.     

Alignment of polymer network-stabilized ferroelectric liquid crystal using a magnetic field

Polymer network-stabilized ferroelectric liquid crystals with homogeneous alignment have been produced in cells without a surface alignment layer. In this technique, a crosslinkable monomer is mixed into a ferroelectric liquid crystal and polymerized in a magnetic field to form a polymer network that will stabilize the alignment of the ferroelectric liquid crystal. The concentration of the monomer is an important factor in achieving alignment of the ferroelectric liquid crystal. Both the morphology of the final composite layer and the molecular alignment of the host FLC are affected by the curing temperature at which the UV curing of the sample is started.     

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.     

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.     

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.     

Synthesis,photo-reaction and photo-induced liquid crystal alignment of soluble polyimide with pendant cinnamate group

In this paper, the synthesis, photo-reaction and photo-induced liquid crystal alignment of a polyimide with a pendant cinnamate group are reported. The polyimide was synthesized by the thermal imidization of the polyamic acid derived from 4,4'-(hexafluoro-isopropylidene)diphthalic anhydride and hydroxydiaminopropane, followed by the attachment of the cinnamate group to the main chain polyimide. The surface of thin layers of the polyimide was found to be preferentially occupied by the pendant cinnamate groups, and liquid crystal alignment on the polyimide thin film exposed to polarized UV was independent of the cinnamate content. The thermal stability of the photo-induced liquid crystal alignment was enhanced with decrease in the cinnamate content. This could be attributed to the strong interchain interaction of the polyimide chains which prevents thermal randomization of the photo-product of the pendant cinnamates. The dependences of the photo-reaction temperature and the annealing temperature of the alignment layer on the azimuthal anchoring energy of the photo-aligned liquid crystal suggest that the local stress developed during the UV irradiation profoundly influences the thermal stability of the liquid crystal alignment.     

Synthesis, photo-reaction and photo-induced liquid crystal alignment of soluble polyimide with pendant cinnamate group

In this paper, the synthesis, photo-reaction and photo-induced liquid crystal alignment of a polyimide with a pendant cinnamate group are reported. The polyimide was synthesized by the thermal imidization of the polyamic acid derived from 4,4'-(hexafluoro-isopropylidene)diphthalic anhydride and hydroxydiaminopropane, followed by the attachment of the cinnamate group to the main chain polyimide. The surface of thin layers of the polyimide was found to be preferentially occupied by the pendant cinnamate groups, and liquid crystal alignment on the polyimide thin film exposed to polarized UV was independent of the cinnamate content. The thermal stability of the photo-induced liquid crystal alignment was enhanced with decrease in the cinnamate content. This could be attributed to the strong interchain interaction of the polyimide chains which prevents thermal randomization of the photo-product of the pendant cinnamates. The dependences of the photo-reaction temperature and the annealing temperature of the alignment layer on the azimuthal anchoring energy of the photo-aligned liquid crystal suggest that the local stress developed during the UV irradiation profoundly influences the thermal stability of the liquid crystal alignment.     

Factors in liquid crystal photoalignment on polymer films: photoorientation versus self-assembly

We demonstrate that photostimulated self-assembly, running in parallel with molecular photoorientation in the top layer of the aligning polymer film, breaks the bulk molecular order mainly determined by the symmetry of irradiation. This may substantially modify liquid crystal (LC) alignment. Depending on the chemical composition of the liquid crystal, the self-assembled layers may influence either homeotropic or planar LC alignment with extremely weak azimuthal anchoring. Effective self-assembly occurs in polymers having side chain chromophores with flexible spacers and polar terminal groups.     

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.     

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.     

Cinnamate-functionalized hyperbranched polymer as liquid crystal photo-alignment layer

In this work, 4-methoxylcinnamoyl chloride was reacted with a commercial hyperbranched polymer （Boltom-TM H30） to prepare a hyperbranched photosensitive polymer （H30-Ci）. The polymer was characterized by UV absorption spectrum and 1H- NMR spectrum. After processed by Linearly Polarized Polymerization （LPP） method, the spin-coated films of H30-Ci were used as photo-alignment layers to assemble liquid crystal （LC） cells containing nematic liquid crystal （5CB）. The observation by polarized microscope showed that the H30-Ci blended with a linear polymer （BP-AN-Ci） photo-alignment layers could align LC molecules in a very uniform way.     

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.     

Investigation on ion movement in the fringe-field switching mode depending on resistivity of alignment layer and dielectric anisotropic sign of liquid crystal

Adsorption and desorption of ions at interface between liquid crystal and alignment layer in liquid crystal displays play a crucial role in residual direct current voltage associated with image sticking. In this article, the dependency of such adsorption and desorption of ions on resistivity of alignment layer and sign of liquid crystal dielectric anisotropy in the fringe-field liquid crystal cell has been investigated. Our studies show that the time constant of ions during adsorption and desorption depends upon resistivity and dielectric constant of liquid crystal and alignment layer, and most strongly influenced by the resistivity of alignment layer such that the one with lower resistivity in two orders shows much faster adsorption and desorption at the interface than that of the one with higher resistivity.