Thet Naing Oo

Effects of monomer/liquid crystal compositions on electro-optical properties of polymer-stabilized blue phase liquid crystal

A polymer-stabilized blue phase liquid crystal is one of the candidates for the next-generation display material. In this study, effects of monomer/liquid crystal compositions on electro-optical characteristics of polymer-stabilized blue phase liquid crystals were investigated. By optimizing monomer/liquid crystal compositions, lower operating voltage, reduction in hysteresis and residual birefringence were achieved. However, some technical issues remain to be overcome.

Electro-optical properties of polymer-stabilized blue phase with different monomer combination and concentration

Electro-optical properties of the polymer-stabilized blue phase (PSBP) liquid crystals (LCs) with different monomer combination and concentration were studied. Kerr constant, voltage-dependent transmittance, response time, residual birefringence and hysteresis were measured for PSBP LCs prepared using acrylate and methacrylate monomer composites. Operating voltages of PSBP LCs prepared by acrylate composites were lower than those of PSBP LCs prepared by methacrylate composites. By contrast, residual birefringence and hysteresis of PSBP LCs prepared by acrylate composites were higher than those of PSBP LCs prepared by methacrylate composites. Faster response and lower hysteresis were observed in PSBP LCs with higher monomer concentration. It was found that monomer combination and concentration strongly affected the electro-optical properties of PSBP LCs.

Study of Liquid Crystal Display Fabricated Using Slit Coater under Two Ultraviolet Irradiation Conditions

We have recently reported on a method that utilizes a slit coater as a novel liquid crystal alignment technique. We carried out this study under two ultraviolet (UV) irradiation conditions, viz., (i) UV irradiation from the side of a glass substrate (exposure type 1) and (ii) UV irradiation from the side of the air–liquid crystal interface (exposure type 2), and investigated the electro-optical characteristics and azimuthal anchoring energy of liquid crystal sample cells performed under these two UV irradiation conditions.

Single-substrate polymer-stabilized blue phase liquid crystal display

We demonstrated a single-substrate polymer-stabilized blue phase liquid crystal (PSBP LC) display using a bar-coating technique. The BP temperature range and the electro-optical (EO) properties of PSBP LC cells fabricated on a single-substrate of glass, polycarbonate (PC) and polyethylene terephthalate (PET) were investigated. It was found that PSBP LC cells fabricated on the single-substrate of glass, PC, and PET exhibited a narrower BP temperature range in comparison with the conventional PSBP LC cell. This is necessary to improve the mechanical stability, the thermal stability and the EO performance of the single-substrate PSBP LC cells.

Surface alignment of liquid crystal multilayers evaporated on photoaligned polyimide film observed by surface profiler

Abstract The investigation of the surface alignment of liquid crystal (LC) multilayers evaporated on photoaligned polyimide vertical alignment (PI-VA) film was carried out by means of the novel three-dimensional (3D) surface profiler. We report the first use of the surface profiler to visualize a microscopic image of the monolayer arrangement of LC molecules in contact with the surface of photo-treated PI-VA film. The photoinduced anisotropy of partially UV-exposed PI-VA film can be visualized as a topological image of LC multilayers. It seems that the topology of LC multilayers is indicating the orientational distribution of LC molecules on the treated film. It was found that the periodically photoaligned PI-VA film surface can align an adsorbed LC monolayer and the LC molecular alignment can be extended to the bulk via the epitaxylike LC–LC interaction, i.e. a short-range molecular interaction. With regard to the unexposed PI-VA film surface, noticeable anisotropy in the monolayer alignment was not observed, indicating that the long-range elastic interaction may be responsible for the bulk alignment. The appearance of small droplets in the masked region may be presumably related to the dewetting phenomena.

Investigation of alignment of nematic liquid crystal on micropatterned polyimide surface

The alignment properties of a nematic liquid crystal in contact with a micropatterned polyimide surface were theoretically analyzed and experimentally investigated. The patterns with a period of 1 µm were formed by stripes of alternating planar and homeotropic anchorings. The theoretical and experimental results implied that domains with the opposite tilt angle of liquid crystal directors were formed inside the cell. The average tilt angle was nearly 45° in the two alignment states and slightly varied from this equilibrium value depending on the treatment method, cell configuration and liquid crystal.

Study of electro-optical properties of liquid crystal/reactive mesogen-coated liquid crystal display fabricated by slit coater

We have recently proposed a slit coater method for printable liquid crystal (LC) devices. In this method, the LC/reactive mesogen (RM) mixture was directly coated uniaxially onto the substrate surface by shear flow between the slit nozzle and the substrate, and the liquid crystalline molecules were anchored by in situ photopolymerisation of RM monomers. In this study, the dependence of electro-optical properties and device parameters of LC sample cells fabricated by the slit coater on ultraviolet (UV) exposure dosage was investigated. Moreover, effects of UV exposure dosage and thermal annealing on the azimuthal anchoring energy of LC sample cells fabricated by the slit coater are presented.

Liquid crystal alignment on patterned-alignment films

To come up with a bistable liquid crystal (LC) device using unpolarized UV light, single-step laser patterning on a photoalignment layer using a photomask was proposed to achieve an equilibrium configuration of LC molecules in contact with a periodically patterned substrate. The patterns were formed by stripes of alternating random planar and homeotropic anchoring on a submicrometer scale in the order of 0.5 μm. Two possible configurations of bistable LC cells that can be obtained by combining a micropatterned surface formed with alternating random-planar- and homeotropic-alignment with planar- or homeotropic-alignment surfaces were proposed. The alignment properties of the two proposed models were investigated, along with the microscopic switching behavior of micropatterned nematic LC cells.

Effects of Host Liquid Crystal Composition on the Stability of Liquid Crystalline Blue Phases

The temperature range of blue phase liquid crystal can be extended through the use of polymer stabilization. In this work, the mixing condition for the host liquid crystal mixture containing E8, PE-5CNF, and CPP-3FF; and the monomer UCL-011 and the chiral dopant NYC-22133L was investigated. Typically, the operating temperature for displays should be in the range of −40 to +80°C. The chiral dopant and monomer tend to lower the clearing temperature; thus, the host LC should have a high BP-Iso clearing temperature. In this work, optimization of the ratio of the host liquid crystal with respect to the monomer was carried out. It was found that a ratio of 5:3:2 for E8: PE-5CNF: CPP-3FF gave a polymer stabilized blue phase of ∼50.4°C. Driving voltage and electro-optic hysteresis was also investigated, yields a conclusion that a trade-off between driving voltage and hysteresis exists for the PSBPLC mixture that was investigated.