摻染料液晶之介電特性

Dielectric Properties of Dye-Doped Liquid Crystals

謝建文(Chien-Wen Hsieh)

指導教授 ： 李偉

中原大學/理學院/應用物理研究所/碩士(2008年)

https://doi.org/10.6840/cycu200900194

摘要

摘要
本研究團隊已成功導入介電頻譜量測技術，藉由此方法可確切導出頻率相依之複介電常數，並對系統的相關物理機制作進一步的了解。此論文探討的重點為介電譜的色散與吸收，旨在研究液晶中染料分子的摻雜在不同電壓、溫度下的介電行為，及其所產生的鬆弛過程，並將結果對應出各種極化模型，以提供我們對材料物性分析上更多的訊息。
整合研究結果如下：
一、低離子濃度之液晶（ZLI-4792）添加染料分子（DB14或MR）會導致鬆弛行為延後於高頻發生，而高離子濃度液晶（E7）樣品則因摻雜染料使得介電損耗提前於低頻反應；
二、在高離子濃度液晶中，染料的加入會抑制低電場作用下液晶分子的再轉動，使複介電頻譜不隨外場改變；
三、當外加電壓超過臨界值後，低離子濃度液晶在所觀察的介電頻譜範圍（20 Hz–2 MHz）內顯出兩個介電吸收峰；
四、高離子濃度液晶中的大量離子會導致材料自1 kHz至低頻的介電虛部上升，此現象並未發生於高阻值之ZLI-4792；
五、隨著溫度的上升，E7分子因極化能力變弱且分子取向機率變為均等，使複介電常數（色散與介電損耗）逐漸趨於定值。

關鍵字

介電頻譜術

並列摘要

Abstract
Our team has successfully implemented dielectric spectroscopy to measure the frequency dependence of the complex dielectric constant, allowing one to investigate the underlying mechanisms present in complex systems such as liquid crystal. In this thesis work, investigated are the dielectric relaxation of both the liquid crystal as well as dye-doped liquid crystal as a function of external bias voltage and temperature.
The results of this investigation can be summarized as follows:
1. For liquid crystal with low ion concentration (ZLI-4792), the relaxation frequency of the dye (DB14 or MR)-doped system has been found higher than that of the undoped one. In contrast, the relaxation frequency becomes lower due to the addition of dye molecules in liquid crystal (E7) with higher ion concentration.
2. The addition of either dye in the high-ion-concentration liquid crystal can suppress the director reorientation in the presence of a low electric field, which, in turn, prohibits the alteration of the dielectric spectra to vary with the external field.
3. Beyond a certain value of an applied voltage, the low-ion- concentration liquid crystal exhibits two dielectric absorption bands in the frequency range (20 Hz–2 MHz) of this study.
4. Massive ions in the high-ion-concentration liquid crystal result in a rise from 1 kHz to the low-frequency region in the dielectric loss spectra, whereas no such rise has been observed in the spectra of doped and undoped ZLI-4792.
5. At elevated temperatures, the E7 molecules possess weaker dipole moment and molecular orientation becomes random, leading to roughly constant complex dielectric constant.

並列關鍵字

dielectric spectroscopy technique

參考文獻

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