向列型液晶參雜奈米碳結構之特性與動態響應量測

Abstract

液晶與奈米碳材料在近幾年中吸引著許多科學家與研究人員的注意。液晶的開關特性更在應用顯示科技上扮演重要角色。然而雜質離子無可避免地存在於液晶當中，它會影響著元件特性。奈米碳材料恰可提供我們一種方式來改善液晶元件的特性。因此在本文當中，我們使用向列型液晶(E7)同時參雜幾種不同的奈米碳材料如多壁奈米碳管(管長5到15微米)、奈米碳纖維、多壁奈米碳管(管長1到2微米)、螺旋奈米碳管、單壁奈米碳管與富勒希(碳60)，將其混合液注入平行排列的液晶盒中並且量測其電容值。實驗結果顯示：液晶參雜奈米碳材料確實能夠抑制雜質離子帶來的離子電荷效應，同時能夠降低臨界電壓與改善遲滯效應。從電容電壓曲線的分析中，液晶參雜多壁奈米碳管(管長5到15微米)比起未參雜液晶能夠改善磁滯寬度34.25% 並降低臨界電壓52.5%。此外，我們定義離子補捉常數來表示每一種奈米碳材料的離子捕捉能力。根據離子補捉常數的排行，多壁奈米碳管(管長5到15微米) 在本實驗的所有奈米碳材料中，有最好抑制離子效應與改善元件特性的能力。

Liquid crystals and carbon nanomaterials have been of high interest recently. The switching behavior of liquid crystals plays an important role on the application of display technologies. However, the inevitable impurity ions exist in liquid crystals and affect the device performance. Carbon nanomaterials as dopants fortuitously supply us alternatives to improve the performances of liquid crystals. In this work, nematic liquid crystals doped with several kinds of carbon nanomaterials including multi-wall carbon nanotubes (tube length 5~15μm), carbon nanofibers, multi-wall carbon nanotubes (tube length 1~2μm), helical carbon nanotubes, single-wall carbon nanotubes and fullerenes(C60) were examined in planar-aligned liquid crystal cells by measuring their electrical properties. As indicated by the measurement results, carbon nanomaterials certainly suppress the ion-charge effect to some degree, simultaneously lowering the threshold voltage and effectively improving the hysteresis width of liquid crystals. From the analysis of capacitance-voltage curve, the liquid crystal doped with MWCNT (tube length 5~15μm) sample reduced the hysteresis width and the threshold voltage 34.25% and 52.5%, respectively lower than the undoped E7 sample. Moreover, we defined and ranked the ion trapping coefficient for each carbon nanomaterials to represent the ability of trapping ions. Based on the results, MWCNT (tube length 5~15μm) served as the best dopants in liquid crystals to suppress the ion-charge effect and improve the performance of the liquid crystal.