UBC Theses and Dissertations
Numerical simulation of liquid crystal hydrodynamics Li, Shancheng
Liquid crystals (LCs) are a state of matter that is intermediate between crystalline solid and amorphous liquid. They are anisotropic viscoelastic materials with broad applications in science and engineering. For example, they have been traditionally used in flat panel displays and more recently, in energy conversion applications. They can also be used as lubricants or additives to lubricants to reduce wear, improve load-carrying capacity and decrease the coefficient of friction (COF) due to their anisotropic viscoelastic properties and their ability to form ordered layers in the vicinity of solid surfaces. The Landau-de Gennes (LdG) equations can model the flow of liquid crystals. The LdG equations are capable of modelling texture formation since defects in liquid crystals correspond to non-singular solutions to the governing partial differential equations (PDEs). In this research, the Landau-de Gennes equations were simplified with Reynolds scaling analysis to form the simplified LdG equations, which were then applied to the Couette geometry and the slider bearing geometry. Both the simplified LdG model and the full LdG model were numerically solved in COMSOL Multiphysics ®. The simplified LdG model was evaluated and verified by comparing simulation results with those from the full LdG model. Lubrication performance was analyzed for the slider bearing geometry with both the simplified LdG model and the full LdG model. The simplified LdG model significantly reduced simulation wall time compared to the full LdG model over the same domains. Chiral liquid crystals are a type of LCs that have a twist or helix about an axis normal to the director. They are used in thermochromic systems and flexible cholesteric displays and exist in virtually all organisms as a building block of life. The Couette flow of chiral liquid crystals was modelled, evaluated and verified in COMSOL. The 2D lid-driven cavity flow of chiral liquid crystals was simulated, evaluated and verified in COMSOL. Parametric studies investigating the effect of the chiral strength and the viscous flow effect on the microstructure of LCs were conducted.
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