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Title: Multiscale modelling and experimental estimation of liquid crystals parameters
Author: Bennett, Thomas Paul
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2017
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In this thesis we investigate two problems: the measurement of nematic liquid crystal material parameters and the modelling of liquid crystal colloids. Specifically we have developed an optical method of measuring liquid crystal viscosities, and by combining multiple measurements of the transmitted intensity we can measure the variations in boundary pre-tilt and cell thickness across a planar cell. We find that it is possible to measure the rotational viscosity γ1 using an amplitude modulated driving potential. This method allows us to probe the dynamics of a nematic liquid crystal across a range of frequencies. In addition we are able to recover the combination of viscosity coefficients α4 + α5 from high voltage high frequency measurements. The model of a nematic colloid that we have developed is based on the asymptotic homogenisation of a Q-tensor model. These colloidal systems are inherently difficult to model as they contain a large range of physically relevant length-scales. The dopant particles disturb the alignment of the nematic locally and complicate the interaction with externally imposed fields. On the macro-scale both the dopant and nematic realign across a length scale of several microns. By using homogenisation we have derived a set of coupled equations for the evolution of the nematic and dopant alignment. The system consists of a set of cell problems solved on the micro-scale which determine effective material parameters and a set of macroscopic equations in which the influence of the dopant is confined contain to effective material parameters. The theory we obtain is accurate for rather arbitrarily shaped metallic dopants. In particular we are able to directly link the geometry, volume concentration and material parameters of the dopants to the behaviour of the macroscopic system.
Supervisor: D'alessandro, Giampaolo ; Kaczmarek, Malgosia ; Daly, Keith Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available