流動效應對液晶顯示器動態響應之影響

Abstract

在液晶元件裡，考慮液晶的流動是準確地模擬液晶元件動態響應 的基本重要條件。在本論文中，我們研究了液晶流動效應對液晶元件 動態響應之影響。我們從艾瑞克森--萊斯利理論出發，利用電腦 模擬來分析幾個目前重要的液晶顯示器操作模式的動態機制。 我們在實驗與模擬中都發現了垂直配向的液晶元件中存在著 類似在向列扭轉液晶元件中發現的光學反躍現象。我們成功地 找出了這個光學反躍的機制以及分析這個光學反躍與原本在向列扭轉 液晶元件中所發現者之不同處。我們的模擬結果和實驗結果也 相當吻合。 另外經由分析模擬結果，我們提出了採用較大的扭轉彈性係數 K_22 的液晶材料可以有效地增快垂直配向液晶元件的響應速度而不會影響 其靜態光電特性。 本論文也對目前常用的向列扭轉液晶元件進行模擬分析。我們發現利用 節距較短的液晶材料可以減低該元件的光學反躍現象及加快響應速度。 從實驗上的觀察，我們預測到垂直配向元件在電場下具有雙穩態，而 在實驗上我們也成功地證實這個預測並利用它發明出新的液晶元件。

The flow of liquid crystal is an essential part to the study of the dynamics of liquid crystal devices. In this work, we investigated the influence of the flow effect on the dynamics behavior of liquid crystal cells. Employing the Ericksen-Leslie theory, we analyzed the transient behavior of several liquid crystal modes by computer simulation. It was found that the optical bounce phenomenon of the transmittance-time curve which originally occurred in twisted nematic liquid crystal cells also appears in the rising period of pure homeotropic and chiral-homeotropic liquid crystal cells. In this work we successfully modeled this optical bounce and found this phenomenon is caused by the flow-induced twist. After analyzing the transient director behavior, we also examined the difference between the optical bounce of the twisted nematic cell and that of homeotropic-like cells. The simulation results agree with the experiments. From the information provided by computer simulation, we found that the response time of homeotropic-like cells can be improved by a larger twist elastic constant with little or no influence on the original static electro-optical properties. The dynamics of the twisted nematic cells were then analyzed. The effects of the chiral dopant in twisted nematic cells were also discovered. It was found that the finite pitch can reduce the optical bounce effect and improves the response time. Based on the observation of the transient transmittance of the pure homeotropic cell, we also predicted the existence of two stable states in the homeotropic liquid crystal cell. Furthermore, from this prediction, we demonstrated a new bistable liquid crystal device which can operate between tree states.