銀奈米粒子摻雜於液晶盒中之介電頻譜分析

Abstract

近來有許多金屬奈米粒子摻雜於液晶盒的應用,例如電控表面電漿共振，及頻率調變的光電特性等,但對於金屬奈米粒子聚集特性對於液晶盒的影響卻沒有更進一步的探討。本論文旨在以非侵入式且即時分析的介電頻譜量測技術探討銀奈米粒子摻入液晶盒的介電特性。由於銀奈米粒子在液晶盒中產生不同大小及形狀的聚集，我們導入Sillars用含形狀意義的去極化因子(depolarization factor)所修正的Maxwell–Wagner方程式(M–W equation)的分析，得出在量測頻段50–105 Hz內銀團簇介電常數皆為正值，對於Kobayashi團隊在2012年提出金屬奈米粒子摻雜於液晶盒中，在低於鬆弛頻率(relaxation frequency)時金屬奈米粒子因為吸附離子雲，進而產生液晶盒電容放大及金屬奈米粒子具負介電常數效果的物理圖像模型，提出了另一可能的解釋。

The applications of liquid crystal devices (LCDs) doped with metal nanoparticles have been investigated intensively and demonstrated recently. However, the study of the influences of the aggregation of nanoparticles on the electro-optical properties of LCDs is scarce. The capacitance amplification of the LCD doped with metal nanoparticles was reported by Kobayashi et. al. recently. They claimed that the phenomenon may be due to a special nature of the oscillating extra charges, which occurred in the region between the LC and nanoparticles, and produced an effective negative dielectric constant of the metal nanoparticles. In this work, we studied the dielectric spectroscopy of LCDs doped with silver nanoparticles in the frequency range of 50–105 Hz. The dielectric spectroscopy of a binary composite material can be well described by the Maxwell–Wagner polarization for spherical particle suspensions. We have observed that the silver nanoparticles aggregated and formed different sizes of clusters in LCDs. Therefore, the Maxwell–Wagner–Sillars model suitable for different shapes of particle suspensions was applied to analyze our data. Our results showed that the dielectric constant of silver clusters in LCDs was positive regardless of frequency, which was different from the results reported by Kobayashi et. al.