The Alignment Behavior of Nematic Liquid Crystal on Micro-grooved Surfaces
Date Issued
2009
Date
2009
Author(s)
Tsao, Ting-Chieh
Abstract
Nowadays, rubbing is the most common method to fabricate alignment layers. Due to the complex mechanism of liquid crystal alignment through rubbing method, many models had been proposed. A well known mechanism proposed by Berreman (1972, 1973) indicated that the alignment was based on strain deformation that makes the free energy to be a minimum as the liquid crystals align along the groove direction. In this study, the alignment of liquid crystal on the micro-grooved surface was investigated through both the simulation and experiment.n the simulation part, modeling liquid crystals aligned on a specific groove system was realized. The Oseen-Frank Equation and Rapini-Papoular form were used respectively for the bulk energy and surface energy of liquid crystal molecules. Making use of calculus of variations, we first deduced the govern equation and its corresponding boundary conditions. Through finite difference method, we could visualize the alignment of the directors in the semi-finite medium and also investigate the pretilt angles and azimuthal angles of various surface geometries and chemical properties.he soft embossing method is proposed to fabricate grating structure on PET (Polyethylene terephthalate) surfaces. These grating PET surfaces are assembled to form liquid crystal cells. It is found that the liquid crystal 4’-n-pentyl-4-cyanobiphenyl(5CB) director uniformly aligns along the groove direction, and the phenomena was consistent with the simulation results. We also formed self–assembled monolayers(SAMs) on the micro-grooved PET surfaces for different surface polarities. By tuning the hydrophobicity of the surfaces, we successfully adjusted the liquid crystal pretilt angle over the whole range from 0° to 90°.
Subjects
Liquid crystal
Alignment layer
Micro-grooved
Pretilt Angle
nano-textured
Type
thesis
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