Investigation of Ionic Effects of a Twisted Nematic Liquid Crystal Cell by Heterodyne-Interferometric Phase Measurements
|關鍵字:||離子效應;相位差量測;Ionic Effects;Phase Measurements|
For the first time, we report the usage of heterodyne-interferometric phase measurements to study electro-optical effects of a rubbed-polyimide-aligned twisted nematic (TN) liquid crystal (LC) cell caused by ionic impurities within the cell. Our experimental results have confirmed that, in some cases, the dominant ionic species in LC mixtures used for TFT-TNs came from impurities of low-ionization-rate(LIR) in agreement with recent publications. However, for the first time, we have observed, in some cases, ions from both high-ionization-rate (HIR) and LIR impurities have existed in the rubbed PI alignment layers of TN cells. Also, for the first time, we have carried out numerical calculations using our ion generation and transport equations to analyze and fit the measured phase data. We have obtained ion concentration and ion mobility for LIR ions within LC mixture and both HIR and LIR ions in the PI alignment layers at different temperatures. From the measured temperature-dependent phase data, we have derived the activation energies of ion-dissociation and ionic mobility of the LC mixture, and activation energies of ion-dissociation of PI alignment layers, within the TN cell. At present, we don’t know the origin and chemical compositions and structures of these HIR and LIR impurities in the LC mixture and rubbed PI films. However, we believe that, by using the experimental and analytical methods reported in this thesis to do further studies on samples of various chemical compositions and process parameters, we can find out the origins as well as chemical and structural properties of these HIR and LIR impurities and their associated ions. We hope that further researches will lead us to realize high-quality and impurity-ion-free rubbed PI alignment layers for TFT-LCDs with high-display qualities without image sticking. Although both phase and intensity measurements can be used to study electro-optical phenomena caused by field-driven net mobile ions accumulated at the interfaces between the LC mixture and the PI alignment layers of the TN cell, we believe that the phase measurement reported in this thesis is more stable and effective. The analytical and experimental methods reported in this thesis can also be applied to study the ionic effects of LC cells made from non-contact LC alignments.