超音波誘發液晶配向層排列之分析

Abstract

配向層聚乙烯醇為長鏈狀分子，在固化過程中，若以無數週期之結構導波所形成的穩定壓力梯度，可誘發配向層分子達成有秩序的排列。本研究將聚乙烯醇層模型化為為具黏滯係數之等向性固體，推導具流體薄層負載之平板結構的聲導波波傳，數值模擬聲導波相速度頻散曲線及各模態的位移、應力、壓力差分佈與質點軌跡，假設聚乙烯醇配向層之厚度與黏度因受熱而改變，推估結構導波產生不同的壓力梯度對其分子排列的影響。數值分析結果顯示，配向層溶液厚度越薄，對結構導波驅動大範圍的配向層排列較為有利，否則應提高表面聲波元件的驅動電壓。配向層溶液黏度越大，或是驅動頻率越高，可以越有效的排列配向層分子。附錄為試片製作與實驗架構，未來可以實驗對照分析結果，作進一步的討論。

After being insonified by a large number of ultrasonic cycles during curing process, the long chain poly-vinyl-alcohol (PVA) molecules could be gradually parallel to one another due to acoustic pressure gradient formed in the alignment layer. The thesis presents an investigation on acoustic guided wave propagation in a PVA layer coated on the glass plate. The PVA layer is modeled as a hypothetical isotropic solid with viscosity. Phase velocity dispersion curves and distributions of displacement, stress, and pressure difference are numerically simulated. The pressure difference changes with the variations in thickness and viscosity of PVA layer. It plays an important role on realignment of PVA molecules. The simulated result indicates that thin and large area of PVA fluid layer can be aligned well by ultrasound, otherwise more energy should be applied. Better alignment can be achieved for the PVA layer with higher viscosity or application of higher-frequency ultrasound. The experimental set up is designed and detailedly described in appendix so that prediction can be compared with experimental results in the future.