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Title: Flow effects in bistable nematic liquid crystal devices
Author: Neilson, Matthew
ISNI:       0000 0001 3440 7341
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2008
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We consider a nematic liquid crystal device in which a bistable surface anchoring term produces two stable states, a Vertical State (i. e. all molecules are homeotropically aligned) and a Hybrid Aligned Nematic (HAN) State (i. e. the molecules are homeotropically aligned on one boundary and homogeneously aligned on the other). Our one-dimensional model determines the director profile throughout a nematic cell by minimizing its free energy. The free energy in this model contains dielectric, elastic, flexoelectric and anchoring terms. This constitutes what we denote the 'no-flow' model. An expanded, so-called 'flow model', also includes a flow equation that we couple with our system of director equations. We then introduce three time integration methods for our numerical simulations, namely an explicit method, a semi-implicit method and a fully-implicit method, each of which employs an adaptive time-stepping algorithm to control the size of each time-step. Numerical simulations also employ a moving mesh algorithm to control the positioning and quantity of node points used at each time-step. We then compare each simulation method to determine which provides the optimal balance of speed and accuracy. We investigate switching for voltage pulses of different magnitude and duration in order to graph standard rV-plots. Each switching region is determined by the interaction between the bistable surface and bulk equations once the applied voltage is removed, which is a relatively complex process. We develop and present a powerful algorithm for automatically generating rV-plots corresponding to any given parameter set. Using this algorithm, we then investigate the effect of each parameter on the switching characteristics of our cell, using both the standard model and the expanded 'flow' model. The effects of flow are investigated by comparing the results of each model via numerical simulation. We show that flow-induced kickback in the director can significantly affect the results obtained using a no-flow model.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral