摻雜不同維度奈米粒子液晶之時變介電特性

Time-Dependent Dielectric Properties of Liquid Crystals Doped with Nanoparticles of Various Dimensions

劉軒宏(Hsuan-Hung Liu)

指導教授 ： 李偉

中原大學/理學院/物理研究所/碩士(2010年)

https://doi.org/10.6840/cycu201000907

摘要

近年以來介電頻譜術應用在液晶研究之發展趨於完整，且在低頻部分（< 101 Hz）已有理論模型可供有效闡述離子的傳輸現象。本論文透過介電頻譜術分析液晶中離子隨時間變化不同的擴散過程，且比較以不同維度的奈米粒子摻雜抑制離子效應的能力，最後探討三維和二維奈米粒子結構在廣泛溫度下的良好抑制離子能力。
藉Uemura所提出的理論對量測數據進行擬合，我們發現無論添加奈米粒子與否，液晶盒在製作完成初期離子都會產生分佈不均勻的現象；隨著時間的增加，離子將透過自然擴散而均勻分散於液晶層中。在摻雜蒙脫土之實驗中，我們找出抑制離子雜質最有效濃度。使用損耗角tanδ 和電模數，我們發現以物理性混合多壁碳奈管和蒙脫土所建構的三維網絡在室溫下有最佳抑制離子雜質的能力。為了使研究更適合應用在液晶顯示器上，我們對摻雜不同維度奈米粒子之液晶樣品進行溫變介電量測。結果顯示在小於50 °C的溫度下，三維奈米結構擁有最佳抑制離子能力；在高溫下（> 50 °C）多二維奈米粒子抑制離子的效果最好。

關鍵字

蒙脫土 ； 液晶 ； 介電 ； 碳奈管

並列摘要

Recently the application of dielectric spectroscopy in the liquid crystal (LC) research has become mature, and the ionic transport can be explained by appropriate theoretical models in the low-frequency regime (< 101 Hz). The present study uses dielectric spectroscopy to investigate the time-varying diffusion behavior of ions in LCs. Comparisons of the suppression ability of the ionic effect are made between various nanoparticle dopants. Finally, the superior reduction in the ionic effect by three-dimensional (3-D) network structure and two-dimensional (2-D) nanoparticles is revealed in the wide temperature range.
Using Uemura’s theory to fit the measured data, we observe the severe unevenness of ionic distribution in cells soon after their fabrication no matter the LCs are doped with or without nanoparticles. The ions then become uniformly distributed with time by the natural process of diffusion. The best concentration of the montmorillonite (MMT) to restrain ions is obtained in the experiment. By the loss angle, tanδ, and the electric modulus, we discover that the 3-D network constructed by physically mixing the multi-wall carbon nanotubes and MMT has the greatest ability to repress the impurity ions at the room temperature. In order to further apply this study to the LC display technology, we perform temperature-dependent dielectric measurements of various samples. Our experimental results show that the 3-D nanostructure has the best ability to reduce the ionic effect at temperatures lower than 50 °C and that the 2-D nanoparticles perform the best at higher temperatures (> 50 °C).

並列關鍵字

montmorillonite ； Dielectric ； Liquid Crystals ； carbon nanotube

參考文獻

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