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Numerical simulations of flow and microstructure in nematic liquid crystalline materials

University of British Columbia

Liquid crystals are known for their anisotropic characteristics, which lead to a preferred orientation of their molecules in the vicinity of solid surfaces. The ability of liquid crystalline materials to form ordered boundary layers with good load-carrying capacity and outstanding lubricating properties has been widely demonstrated. In order to study the advantages of implementing liquid crystals as lubricants, the steady state/time transient isothermal flow of thermotropic/lyotropic, nematic/chiral nematic liquid crystals between two concentric/eccentric cylinders and in planar Couette geometries were studied numerically. To consider the influence of the microstructure formation/evolution on the macro-scale attributes of the flow, the Leslie-Ericksen and Landau-de Gennes theories were employed. Simplicity of the Leslie-Ericksen theory in capturing the orientational alignment angle of the molecules makes it a viable candidate for modelling the flow of flow-aligning nematic liquid crystals. On the other hand, the Landau-de Gennes nematodynamics equations are well suited for predicting texture formation since defects and disclinations are non-singular solutions of the governing equations. The Landau-de Gennes theory for the liquid crystalline microstructure along with continuity and momentum equations were solved simultaneously using General PDE and Laminar Flow modules of COMSOL Multiphysics. The investigation of flow characteristics and orientation of liquid crystalline molecules for different rotational velocities/shear rates and anchoring angles at the boundaries were presented. Furthermore, nucleation and evolution of singularities in texture of the liquid crystalline materials were tracked over the simulation time. Moreover, alterations in the macro-scale attributes of the flow such as velocity profile, pressure distribution and first normal stress difference along with the evolution of defects were studied inside the liquid crystalline domain. The implementation of Landau-de Gennes nematodynamic governing equations for LCs flow simulations offered an insight in application of these materials as lubricants. It was shown the LCs could provide protection against the wearing mechanism by forming a shielding layer in the vicinity of solid surfaces. Three-dimensional simulations of a simplified prosthetic hip joint suggested that liquid crystalline materials should be considered as potential bio-lubricants.

Text

2013-09-26

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/45131

Mechanical Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/