摻雜不同維度奈米碳材之液晶的低頻介電特性

Abstract

近年來，本研究團隊研究液晶盒中之離子效應，在相關的發表中均證實，摻雜微量奈米粒子於液晶（liquid crystal; LC)中，可有效降低液晶盒中之離子雜質濃度，達到抑制離子效應的效果。本論文以先前之研究為基礎，針對碳奈米材料/液晶之膠體結構，以低頻介電頻譜術以及利用Barbero所提出之擬合公式求出離子濃度，探討具不同維度之碳奈米材料在單一、二元以及三元混合並摻雜於液晶的條件下，對於液晶盒中可移動離子之影響。 本研究使用之碳奈米材料包含零維碳60 （C60），一維奈米碳管（carbon nanotubes; CNT）以及二維石墨烯片（graphene nanoplatelets; GNP）。由實驗結果得知，和純液晶相比，摻雜單一碳材於液晶中，隨著碳材之維度增加，其降低離子濃度的比例愈大。另一方面，經由二元與三元混合多種碳材於液晶中，我們發現，和各別單一碳材/液晶相比，可更有效降低離子濃度。其中，以三種碳奈材以各自之最佳濃度摻雜於液晶中所建構之三元混合樣品，其吸附離子的效果最佳。根據上述結果，吾人認為，各類碳奈材具有吸附特定種類之離子雜質的特性。同時推測，在三元混合條件下，分散於液晶中之不同維度碳奈材並不會過度擁擠而引起展透效應。

It has been confirmed by our recent researches that the dispersion of a proper amount of nanomaterial in a liquid crystal (LC) cell enables the reduction in ionic concentration effectively. Based on this key result, in present study, ionic properties of LC cells doped with single, and binary- and ternary-mixed carbon-based nanomaterials were investigated by means of dielectric spectroscopy. By using Barbero’s theoretical model to fit dielectric spectra of each cell, the dopant effect of carbon-based nanomaterial with different dimensions on the ionic concentration in LC cells were discussed. Three types of carbon-based nanomaterial were used in this study. They are zero-dimensional buckminsterfullerene (0D-C60), one-dimensional carbon nanotubes (1D-CNT), and two-dimensional graphene nanoplatelets (2D-GNP). Experimental results show that the ratio on reducing ionic concentration of single-doped LC cells, compared to that of pure counterpart, is promoted with increasing the dimension of nanodopant. Furthermore, we found that binary- and ternary-mixing carbon nanodopant, and then dispersing into LC cells lead to the reduction in ionic concentration more effectively. Among the cells with different dopant-conditions, we concluded that the ternary-doped LC cell constructed by doping C60, CNT, and GNP with their corresponding optimized concentrations reveals best ability on suppressing ionic effect. According to abovementioned results, it is suggested that certain type of carbon nanomaterial is responsible for restraining specific types of impurity ions. In addition, it also implies that the percolation effect does not obtained in the ternary-doped cell.