| Summary: | 博士 === 國立臺灣大學 === 化學工程學研究所 === 106 === This thesis focuses on the effects of surface properties on various systems, and is composed of three parts: 1. Study the surface properties influence on the pretilt angle control of polymer-stabilized liquid crystal system. 2. Control and optimize the contact angle asymmetry on the hydrophobic triangular post patterned surface. 3. Investigate the directional wicking phenomenon on the hydrophilic triangular post structured surface.
This work utilizes two-component monomers to control the LC pretilt angle, and study the surface property change and the influence on the LC pretilt angle. By tuning the monomer concentration, the pretilt angle is successfully tuned from 0.8° to 90°. During the polymerization, the polymer deposits onto the substrates and modifies the surface to a lower surface energy and a higher roughness. These two effects increase both the LC pretilt angle and water advancing contact angle of the substrates. As a consequence, the ACA of substrates reflects the tendency of pretilt angle and can be used as an index for pretilt angle control.
Asymmetric contact angles are observed on the hydrophobic triangular post structure; the advancing and receding contact angles are higher in the base direction than the ones in the tip direction. This asymmetric property is affected by the structure packing density and the post height. The asymmetry is enhanced as the packing density is increased. However, increasing the post height deteriorates the asymmetry. While as the packing density and the post height reach a certain condition, a strong pinning occurs in the tip direction, which greatly raises the contact angle and destroys the asymmetry. This work is studied with both experiments and simulations. A recommendation of structure geometry for optimized asymmetry is given and the strong pinning is predicted.
In the last part of this research, the directional wicking behavior is realized with the hydrophilic triangular post structured surface. Surface Evolver calculates the stability of liquid film on given geometry to predict the conditions for spontaneous wicking. The base direction is found to effectively prevent the liquid spreading. The wicking in the tip and side direction are found simultaneous. To distinguish the wicking conditions for the tip and side direction, an asymmetric arrangement is necessary. By analyzing the structure influence on the wicking conditions, the wicking behaviors on the structure of asymmetric arrangement can be simply and quickly predicted. Finally, the wicking behaviors obtained from the calculation are examined with experiments.
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