超分子液晶膠用於散射元件之特性研究

本論文旨在探討超分子液晶膠之製作與在光電元件上的應用。液晶膠為液晶和固態凝膠因子的混合物，已被廣泛應用在光電領域中，如：高導電度的液晶半導體、快速反應的光調頻元件。在這個研究中，我們使用了芴系共聚物(Polyflourene)作為凝膠因子，此類凝膠因子會因其共軛π電子結構而自我組裝、並與液晶相互牽引，形成有序的網絡狀結構，有助於大幅降低元件的驅動電壓。實驗中，我們配製不同濃度的凝膠因子與液晶混和物，將其加熱至使液晶呈均向態(isotropic)，再將其注入液晶晶胞元件中(內部鍍有ITO導電玻璃和配向層)，利用兩物質相變溫度的不同，使得降溫過程中，液晶會先變為液晶態並產生方向性，排列凝膠因子；待降至凝膠因子的膠化溫度後，開始自我組裝形成有序的網絡狀結構。根據在降溫過程中，排列液晶的方法，我們的研究分為兩個方向：首先是利用晶胞內的配向層排列液晶，可製作出反向模式(reverse mode)的散射元件，能在凝膠因子的長鏈方向產生明顯的異向性散射(1:300)，並只需以極低的電壓(< 2V)就可達到；之後我們更進一步在降溫時施加偏壓於液晶晶胞上，改用電場排列液晶，可製作出順向模式(normal mode)的散射元件，不需驅動即能產生異向性散射(1:300)，且低電壓下(<2V)即可切換為透明態。以上兩系列的元件在不同的晶胞配向模式中皆被實作出來，因此我們認為用芴系共聚物凝膠因子製作液晶膠，是一種應用廣泛的材料，能應用在低功耗智慧型節能玻璃、可調控式偏振片、偏振光調制器等諸多光電元件上，極具潛力。

關鍵字

液晶膠；異向性散射；芴系共聚物；電控切換元件；自我組裝結構

並列摘要

In this thesis, we investigate the electro-optical properties of supramolecular liquid crystal gel. Liquid crystal gel, the mixture of liquid crystal and solid-state gelator, has been widely used in several devices such as: liquid crystal semiconductors with high conductivity, fast response phase modulators, stabilization of the orientation of ferroelectric LCs. In this work, we used a polyfluorene-based polymer as gelator since it could form a ordered network structure by self-assembly to align LC molecules. In order to fabricate a scattering device using LC gel, first of all, we heated the gelator / LC host mixture over the nematic-isotropic temperature of the LC. After that, we injected it into LC cells and cooled it to room temperature. Due to the different phase transition temperature of these two materials, LC transits to nematic phase during the cooling process first and begins to align the gelator molecules. After the temperature further decreased below the solvent-gel transition point of gelator, ordered network structure would formed in the cell and hence a scattering device could be obtained. According to the different cooling process, our devices can be divided into two types: First, without external electric field, reverse-mode scattering device was obtained. The best contrast ratio is up to 270 with extremely low driving voltage (<2V). Furthermore, by applying external electric field during the cooling process, normal-mode scattering device was obtained. The best contrast ratio is up to 330 with extremely low driving voltage (<2V). Both of these two types of devices demonstrate superior electro-optical properties. Therefore, we suggest that the LC gel with supramolecular gelator is a promising material for wide range of application such as: low power consumption smart windows, switchable polarizers, polarized light modulators.