(A) study on fabrication of liquid crystal cell using soft lithography and behavior of liquid crystal on polymer surface

Abstract

In this thesis, the mechanical stability and the uniform alignment of a flexible liquid crystal cell have been achieved by introducing micro- or nano-structure on a cell substrate using soft lithographic techniques. In chapter 2, a variety of methods to improve the mechanical stability of a liquid crystal cell have been investigated. The uniform cell gap between two substrates and the mechanical stability can be guaranteed by introducing columnar spacers via soft lithographic approaches. First, a period array of columnar spacers was fabricated via micromolding in capillary (MIMIC) method using a polydimethylsiloxane (PDMS) elastomeric mold. The mechanical stability has more improved when polyimide (PI), the same material as that of alignment layer for the LCD, was selected for the spacers. Second, a flexible liquid crystal cell based on an elastomeric substrate having microstructures has been suggested. A micropatterned PDMS elastomeric film can be simply fabricated by replica molding method. The micropatterned PDMS film has been directly used as an upper substrate for liquid crystal cell. Microstructures on the PDMS film have functioned as spacers for uniform cell gap when assembled by direct contact between two substrates into a liquid crystal cell. In chapter 3, we have investigated the behavior of liquid crystal molecules on a nano-level surface topography. First, nano-scratches has been formed on the surface a PDMS elastomeric film, and liquid crystal molecules have aligned along to the scratched direction. Second, we have fabricated polyacrylate (PA) substrate having a nanopatterned structures using a soft-imprint technique. The planar alignment of liquid crystals along the direction of nanogrooves has been generated. Twisting behavior of nematic liquid crystals has been also observed with a perpendicular assembled liquid crystal cell and the cell parameters can be estimated by using the Soutar and Lu method. By comparing the anchoring energies obta...