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.     

Preliminary communication Investigation of pretilt angle generation in nematic liquid crystal with oblique non-polarized UV light irradiation on polyimide films

We investigated new rubbing-free techniques for liquid crystal (LC) alignment with non- polarized ultraviolet (UV) light irradiation on plates coated with two kinds of the polyimide (PI) films. It was found that monodomain alignment of nematic (N) LC is obtained in the cell having a PI surface without a side chain. We successfully observed that the generated pretilt angle of the NLC is about 3 with an angle of incidence of 70 on the PI surface without side chains. This pretilt angle generation is attributed to interaction between the LC molecules and the polymer surfaces; the uniform alignment of NLC is attributed to anisotropic dispersion force effects due to photo-depolymerization of polymer on PI surfaces.     

Novel alignment method for control of high pretilt angle by using a solvent dipping effect on polymer surfaces

A novel alignment method for control of high pretilt angle in nematic liquid crystals (NLC), using a solvent dipping effect on various alignment layers, was successfully investigated. The pretilt angle of a NLC is increased by dipping before rubbing treatment on three kinds of rubbed polyimide (PI) surfaces. The pretilt generated by the dipping after rubbing a PI surface with a short side chain is high compared with a PI surface with a long side chain. The pretilt generated by dipping before rubbing homeotropic layer of a positive type NLC (δε > 0) is lower than that of the negative type NLC (δε < 0). The generated NLC pretilt angle is attributed to the perpendicular component of the permittivity epsilon of the NLC.     

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.     

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.     

Preliminary Communication : Generation of high pretilt angles of nematic liquid crystal (5CB) on rubbed organic solvent soluble polyimide surfaces with helical backbone structure and trifluoromethyl moieties

High pretilt angles of nematic liquid crystals (NLC) have been successfully generated on rubbed organic solvent soluble polyimide (PI) surfaces with a helical backbone structure and trifluoromethyl moieties. We have found that the pretilt angle of in 4-n-penty-4-cyanobiphenyl (5CB) on rubbed PI surfaces with trifluoromethyl moieties attached to the lateral benzene rings is larger compared to that on rubbed PI surfaces with trifluoromethyl moieties attached to the polymer backbone. The observed pretilt angle of 5CB on unidirectionally rubbed PI surfaces with trifluoromethyl moieties attached to the lateral benzene rings is about 15 degrees in the wide rubbing region. From these results, it is expected that the microscopic surface structure of the polymer strongly contributes to the pretilt angle generation of the LCs at the surface.     

Effect of pretilt angle on the polar anchoring energy in NLCs on weakly rubbed polyimide surfaces

The polar anchoring strength and pretilt angle generation in nematic liquid crystals (NLCs), on three kinds of rubbed polyimide (PI) surfaces, were investigated. The pretilt angle generated in 4-n-pentyl-4'-cyanobiphenyl (5CB) is large compared with ZLI-4792 (a fluorinated mixture type NLC) for all rubbed PI surfaces. The high pretilt angle in 5CB is attributed to a much larger birefringence and much larger perpendicular component of permittivity. The polar anchoring energy of ZLI-4792 is high compared with 5CB on all rubbed PI surfaces for a weak rubbing strength. It is suggested that the high anchoring energy of ZLI-4792 may be attributed to the low NLC pretilt angle.     

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.     

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 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.     

Fast response in TN liquid-crystal cells: effect of functionalised carbon nanotubes

The optical response time of a nematic liquid crystal (NLC) decreases due to incorporation of carbon nanotubes (CNTs) in the liquid-crystal host. Such reduction is believed to be due to an increase in the elastic constant of the nanotube-doped LC system. In this paper, we present the effect on optical response due to doping an NLC with octadecylamine functionalised single-walled carbon nanotubes (ODA-SWCNT) in a twisted alignment mode. The electro-optic switching amplitude of ODA-SWCNT nanocomposites of NLC decreases compared to pure NLC. A fast response time is observed with an increase in the concentration of ODA-SWCNT in NLC host. Additionally, optical response of pure NLC in a twisted nematic (TN) cell fabricated using mixtures of polyimide (PI) and ODA-SWCNT as an alignment layer is investigated. The optical response time decreased by ~75% in a TN cell fabricated with a mixture of PI and ODA-SWCNT compared to that of a TN cell prepared using a pure PI alignment layer. The presence of ODA-SWCNT in the alignment layer enhances the surface anchoring of the NLC molecules leading to an increase in the elastic constant and a decrease in the optical response time of NLC.     

Zigzag defect-free alignment of surface stabilized ferroelectric liquid crystal cells with a polyimide irradiated by polarized UV light

Zigzag defect-free surface stabilized ferroelectric liquid crystal (SSFLC) cells were prepared using a photodegradable polyimide (PI) having a cyclobutane ring in the backbone. The PI layers were irradiated by polarized ultraviolet light (PUVL) at normal incidence to the surface, and characterized by UV and FTIR spectroscopy. The anisotropy originates from preferential cleavage of PI chains oriented parallel to the polarization direction of the irradiating PUVL. After the polarized UV light irradiation, the PI surface was much flatter than that after rubbing, but it induced a similar order parameter of dye-doped nematic LC molecules to that for a rubbed cell. Alignment of both the FLC molecules and the layer structure is important in SSFLC. After 40 min irradiation, the FLC molecules were well aligned homogeneously, and the FLC cells showed a uniform texture without zigzag defects which also indicates a well aligned layer structure. Zigzag defect-free alignment may result from the flatter surface, the much smaller and more constant pretilt angles, and the bigger cone angle than those achieved by rubbing.     

Zigzag defect-free alignment of surface stabilized ferroelectric liquid crystal cells with a polyimide irradiated by polarized UV light

Zigzag defect-free surface stabilized ferroelectric liquid crystal (SSFLC) cells were prepared using a photodegradable polyimide (PI) having a cyclobutane ring in the backbone. The PI layers were irradiated by polarized ultraviolet light (PUVL) at normal incidence to the surface, and characterized by UV and FTIR spectroscopy. The anisotropy originates from preferential cleavage of PI chains oriented parallel to the polarization direction of the irradiating PUVL. After the polarized UV light irradiation, the PI surface was much flatter than that after rubbing, but it induced a similar order parameter of dye-doped nematic LC molecules to that for a rubbed cell. Alignment of both the FLC molecules and the layer structure is important in SSFLC. After 40 min irradiation, the FLC molecules were well aligned homogeneously, and the FLC cells showed a uniform texture without zigzag defects which also indicates a well aligned layer structure. Zigzag defect-free alignment may result from the flatter surface, the much smaller and more constant pretilt angles, and the bigger cone angle than those achieved by rubbing.     

Effect of an electric field applied during the injection procedure on the pretilt angle of a nematic liquid crystal

We examined the effect of an electric field applied during the injection procedure on the polar pretilt angle of a nematic liquid crystal (LC). The pretilt angle of the sample injected at 25°C gradually increased as the electric field was increased. On the other hand, the pretilt angle of a sample injected at 90°C (which is above the nematic-isotropic phase transition temperature of LC) showed a sudden increase in the presence of the electric field and also increased with a greater electric field. We think the alignment layer might be swollen with LC molecules, and the rotation of the immersed LC molecules by the electric field induces a deformation of the alignment layer. These results imply LC and the alignment layer were coupled, and their cooperation had an influence on determining the bulk pretilt angle.     

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.     

Investigation of electro-optical characteristics of photo-aligned TN-LCDs on PCEMA surfaces

In this work, a novel photo-alignment material, poly(cinnamolyethyl methacrylate) (PCEMA), was synthesized by photo-dimerization. We investigated the electro-optical characteristics of twisted nematic (TN)-liquid crystal displays (LCDs) photo-aligned with linearly polarized UV light irradiation at normal direction on the PCEMA surfaces. Excellent voltagetransmittance characteristics were observed. The threshold voltage of the photo-aligned TN-LCD decreases with increasing UV irradiation time. Additionally, response times are almost the same as for a rubbing-aligned TN-LCD.