染料與液晶混合物的導電率與秩序參數之關係

Abstract

本論文旨在探討將不同化學結構的二色性染料摻入向列型液晶所產生之介電特性與光學效應。本實驗使用染料化合物結構可分為偶氮型與蒽醌型，液晶材料選用向列型液晶E7。吾人將兩者混合物樣品經由介電頻譜量測以觀察離子電荷對於介電之影響。另一方面，實驗中所使用之染料亦具有光學二色性現象，其反應過程將形成主客效應。因此，本研究以可見光作為光源，利用光譜儀量測二色性染料其水平與垂直方向吸收光譜圖，且運用公式計算各類染料之光吸收率與秩序參數。研究結果顯示，本實驗量測各染料間之介電虛部差異，源於液晶盒內染料與液晶混合物所形成之分子間作用力。在染料分子主鏈上具有單鍵、雙鍵交替之共軛結構，使電子或電荷沿著分子鏈或跨分子鏈運動；由於介電虛部與導電率呈正相關性，因此分子間行為直接影響混合物之整體導電率。相對於染料的色彩顯現，其色澤亦與化合物中分子共軛結構存在著關聯性。本論文揭示染料分子間共軛結構連續性對於混合物中秩序參數與導電率之影響極為顯著。

In this study, Dielectric characteristics and optical effects of nematic liquid crystals (NLCs) doped with different types of dichroic dyes are investigated by means of dielectric and absorption spectroscopies. The dichroic dyes used in this study are divided into two types; azo and anthraquinone dyes, according to their chemical structures. Dielectric spectroscopy was employed to determine the effect of ionic charge transport in the dye-LC mixtures. In addition, absorption spectra of dye-LCs were measured to obtain the parallel and perpendicular components of absorptivity of dye molecules. Finally, mathematical calculation on the order parameter of dye-LC cells were performed according to the results on absorption spectra. Experimental results show that the difference of the imaginary part of dielectric permittivity of dye-LCs as a function of dopant concentration result from the intermolecular forces between the LC and dye in the cells. For the dye materials having conjugated structure with alternative connecting of single and dobule bonds in their main chain, electrons or charges are allowed to move along the molecular chains or the cross-chains. Because of the positive correlation between the imaginary parts of dielectric and the conductivity, it is implied that the overall conductivity of compound is directly impacted by the intermolecular behaviors as well. Furthermore, this study reveals the significant impact of continuity of the intermolecular conjugated structure on the order parameter and conductivitiy of the mixure.