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Three dimensional finite element modelling of liquid crystal electro-hydrodynamics

Willman, E.J.; (2009) Three dimensional finite element modelling of liquid crystal electro-hydrodynamics. Doctoral thesis , UCL (University College London).

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Liquid crystals (LC) are used in new applications of increasing complexity and smaller dimensions. This includes complicated electrode patterns and devices incorporating three dimensional geometric shapes, e.g. grating surfaces and colloidal dispersions. In these cases, defects in the liquid crystal director field often play an important part in the operation of the device. Modelling of these devices not only allows for a faster and cheaper means of optimising the design, but sometimes also provides information that would be difficult to obtain experimentally. As device dimensions shrink and complex geometries are introduced, one and two dimensional approximations become increasingly inaccurate. For this reason, a three dimensional finite element computer model for calculating the liquid crystal electro-hydrodynamics is programmed. The program uses the Q-tensor description allowing for variations in the liquid crystal order and is capable of accurately modelling defects in the director field. The aligning effect solid surfaces has on liquid crystals, known as anchoring, is essential to the operation of nearly all LC devices. A simplifying assumption often made in LC modelling is that of strong anchoring (the LC orientation is fixed at the LC- solid surface interface). However, in small scale structures with high electric fields and curved surfaces this assumption is often not accurate. A general expression that can be used to represent various weak anchoring types in the Landau-de Gennes theory is introduced. It is shown how experimentally measurable values can be assigned to the coefficients of the expression. Using the Q-tensor model incorporating the weak anchoring expression, the operation of the Post Aligned Bistable Nematic (PABN) device is modelled. Two stable states, one of higher and the other of lower director tilt angle, are identified. Then, the switching dynamics between these two states is simulated.

Type: Thesis (Doctoral)
Title: Three dimensional finite element modelling of liquid crystal electro-hydrodynamics
Language: English
Additional information: Authorisation for digitisation not received
UCL classification: UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Electronic and Electrical Eng
URI: https://discovery.ucl.ac.uk/id/eprint/16162
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