We have proposed a hybrid alignment nematic (HAN) liquid crystal cell using a polymer stabilized (PS) technology. The cell shows a reverse mode scattering property. The PS-HAN cell is transparent at any viewing angle in the off-state and has an asymmetrical scattering property at incident angles in the on-state. Applying the cell to a smart glass, it cell can selectively scatter a midday sunlight with a function of window blinds. In this study, two polymerization processes, an irradiation with UV light from planar and vertical aligned sides of the cell have been investigated. UV penetration depth has also been estimated from planar and vertical aligned sides of the cell. LC materials with different UV absorption spectra were prepared. A driving voltage, an optical property and a polymer morphology were measured in PS-HAN cells. The UV intensity profile have an effect on polymer density and particle size, which changed the driving voltage and the light scattering property in the PS-HAN cell. The study on the UV penetration in the polymer stabilized technology can improve their performance.
Liquid crystal (LC) cells with plural latent images have been proposed for security devices. The photo crosslinkable
polymer surface is irradiated with unpolarized UV light through the photo-mask and subsequently rubbed. The LC aligns
parallel and perpendicular to the rubbing direction on the UV irradiated and unirradiated surfaces, respectively. A guest
host mode LC cell is prepared using our alignment patterned substrates. Double-faced optical writing is also successfully
demonstrated in the guest host mode LC cell by exposing from both sides of the cell with unpolarized UV light. The LC
cell is uniformly colored under the natural ambient light. Two latent images can individually be visualized when a
polarizer is replaced in front of and behind the cell. The third latent image is obtained as a result of logical operation for
two patterned images when the LC cell is set between the polarizer and analyzer. We can see three domains, that is,
transparent, colored and black domains. Each part shows the result of the logic operation of two images, that is, "AND",
"NOT" and "EOR". The alignment patterned LC cell is also utilized as a key cell to visualize the latent information in
the LC cell.
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 <i>K<sub>11</sub></i>, <i>K<sub>22</sub></i> and <i>K<sub>33</sub></i>.
We propose optical phase-control devices using a liquid crystal (LC) material without applying a voltage, and demonstrate a composite alignment of LC molecules on a substrate with a patterned photo-resist film, where LC molecules are partly aligned parallel and perpendicular directions divided into very small areas on the substrate. The patterned film such as randomly distributed circular areas of small diameter size is fabricated by using a photo-mask and a photolithography technique. The LC cells are prepared using the locally composite alignment substrate and a perpendicular alignment substrate. The optical phase of the transmission light through the different pattern density regions was measured. Then, it is found that the optical retardation of the higher pattern density region is larger than that of the lower one.
Techniques of polarized latent image formations on liquid crystal (LC) cells have been proposed for optical security devices. The glass plate coated with a photo-reactive polymer film is prepared as a substrate of the LC cell. The polymer surface is rubbed and subsequently modified by exposing with a non-polarized UV light through the photo-mask. The LC cell using the patterned substrate surface is homogeneously transparent under the normal condition (without polarizers). However, the image with continuous grey levels appears when the cell is set between two polarizers. The latent image can also be optically and thermally written on the cell filled with the LC. The guest-host LC cell which has dual latent images is also demonstrated using another photo-reactive polymer. The LC alignment on both substrate surfaces are respectively patterned by the photo modification and rubbing. The latent image can individually be visible and selected by replacing the polarizer in front or behind the LC cell. Our LC patterning process is very simple compared to other patterning methods and the patterning technique which is utilized the mechanical rubbing and photo modification gives great advantages of not only the large area but also the high density patterning.
Liquid crystal cells with a radial molecular orientation is proposed using a UV curable liquid crystal material. A radially and homogeneously aligned LC cell (RH-LC cell) and an LC cell with a radial molecular orientation on both substrates (RR-LC cell) are fabricated and their optical properties are investigated. A polarization converting function of the RH-LC cell and detecting function of the polarization direction in the dye doped RR-LC cell are confirmed. Furthermore, an optical alignment of liquid crystal on the PVC surface is demonstrated using RH-LC cell.