Rumiko Yamaguchi

Dynamics of surface memory effect in liquid crystal alignment on reconfigurable microwrinkles

Microwrinkles generated by thin film buckling on elastic substrates serve as reconfigurable microgrooves that can align nematic liquid crystals (NLCs). Through rapid switching of the groove direction to generate controlled perturbation in surface-induced NLC alignment, we studied the dynamical behavior of the surface memory effect. Combined with annealing that resets the alignment memory, the time-dependent response to groove switching indicates that substantial memory develops in a few seconds after contact between the surface and the nematic phase.

Dielectric and Electro-Optical Properties of Liquid Crystals Doped with Diamond Nanoparticles

Dielectric and electro-optical properties of nematic liquid crystals (LCs) doped with diamond nanoparticles (DNPs) have been investigated. It is established that the effect of DNPs on the electric conductivity depends on the purity of LC; the nanoparticles adsorb ions from LCs with a substantial content of ionic impurities, but release their own ions in highly pure LCs. The DNPs also influence LC permittivity due to orientational disordering of LC and contribution to overall permittivity of the samples. In contrast to LC-Carbon Nanotubes counterparts, the LC-DNPs composites do not show memory type electro-optic switching that may be assigned to isotropic shape of DNPs and their relatively weak interaction with LC hosts.

Liquid-crystal variable-focus lenses with a spatially-distributed tilt angles

A pretilt angle controlling method by the density of rubbings using a tiny stylus is proposed. The control of the surface pretilt angle is achieved by rubbing a side-chain type polyimide film for a homeotropic alignment. Smooth liquid crystal (LC) director distribution in the bulk layer is successfully obtained even though the rough surface orientation. This approach is applied to LC cylindrical and rectangular lenses with a variable-focusing function. The distribution profile of the rubbing pitch (the reciprocal of the rubbing density) for small aberration is determined to be quadratic. The variable focusing function is successfully achieved in the LC rectangular lens, and the voltage dependence of the focal length is tried to be explained by the LC molecular reorientation behavior.

Reverse-Mode Liquid Crystal Gels with Twisted Orientation

Anisotropic gel films with a twisted molecular orientation of a photopolymerized liquid crystal acrylate and a conventional liquid crystal are demonstrated. The gel films are free of haze at all angles of incident light. Upon application of a voltage across the gel films, the films assume a strong light scattering state with no polarizers. Their contrast ratio and viewing angle properties are improved by increasing twist angle from 90 to 270°.

Liquid-Crystal Blazed Gratings with Spatially Distributed Pretilt Angle

An electrically tunable liquid-crystal (LC) blazed grating was demonstrated by introducing a periodic pattern of pretilt angle that was controlled by adjusting the rubbing density. In the proposed LC grating, an asymmetrically varying LC molecular orientation was realized even without voltage application. The diffracted light intensity was controlled by adjusting the applied voltage, and the diffraction effect disappeared under a sufficiently high applied voltage. Asymmetric diffraction patterns were obtained and it was revealed that 0th-, 1st-, and 2nd-order diffraction beams can be switched with an appropriate applied voltage. A maximum diffraction efficiency of 0.68 for the 1st-order diffraction was experimentally obtained; however, it is much less than the theoretical limit of unity. It is likely that the difference between optical path lengths for extraordinary and ordinary rays is not linearly distributed.

Liquid Crystal Microlens Driven by Two Voltages

A liquid crystal microlens driven by two voltages are reported. The two voltages cooperate to build up an axially symmetrical but spatially nonuniform electric field in a liquid crystal layer in the cell. One of the voltages remain unchanged biasing the reorientation of the liquid crystal directors outside the lens area, while the other one varies to adjust the gradient of the electric field in the lens area of the liquid crystal layer, and hence the properties of the lens. The focal length of the microlens increases monotonically with controlling voltage.

Liquid Crystal Material Dependence on Rubbed PVCi Alignment Properties

We report that the in-plane alignment direction changes by liquid crystal materials on a rubbed polyvinyl-cinnamate (PVCi) film surface. The alignment direction of almost LCs investigated in this study was perpendicular to the rubbing direction. However, a few LCs, for example, MBBA (N-p-methoxybenzylidene p-n-butylaniline) aligned parallel to the rubbing direction. On the other hand, all LCs investigated aligned perpendicular to the polarization direction of the UV light on the photo-alignment PVCi surface. Moreover, the alignment direction of MBBA changed perpendicular to parallel to the rubbing direction with the passage of time after MBBA was put on the irradiated with UV light and subsequently rubbed PVCi surface. These results suggest that the alignment surface is changed by wetting with the LC.

Photo Degradation Properties of Liquid Crystal Cell Using Focused Blue-Violet Laser Beam

Degradation of liquid crystal cell under a blue-violet laser beam irradiation has been investigated for an evaluation of a LC cell photostability. The laser beam was focused on the LC layer in the cell. A far field pattern (FFP) was caused by the change of the LC alignment at the focused point after a few minutes irradiation. The FFP changed as a progress of the alignment degradation and it depended on LC materials, polymer materials and their combinations.

Multidomain Liquid Crystal Alignment properties on Anchoring Controllable Polymer Surface

We have proposed the multidomain patterning of a liquid crystal (LC) alignment by controlling the anchoring strength of alignment surfaces. The azimuthal anchoring strength of rubbed polyvinyl cinnamate (PVCi) is increased by the crosslinking reaction under the unpolarized UV light exposure. The multidomain patterning of twist angle from 0 to 90 degree has been successfully demonstrated in the LC cell using the polyimide coated substrate with strong anchoring and PVCi coated substrate with multi anchoring strength, even though both substrate surfaces are uniformly rubbed and rubbing directions cross at right angles. The twist angle of the LC orientation has been calculated using the torque balance equation. The twist angle in the practical LC cell is consistent with the calculated one. The LC director distribution has also been numerically and experimentally analyzed in the LC cell with one-dimensional periodic change of the anchoring strength. The twist angle distribution is strongly affected by the periodic size, as well as the anchoring strength, the cell thickness and elastic strain energies of K11, K22 and K33.