The Library
Active and passive nematic multipoles
Tools
Houston, Alexander James Hamilton (2022) Active and passive nematic multipoles. PhD thesis, University of Warwick.
|
PDF
WRAP_THESIS_Houston_2022.pdf - Submitted Version - Requires a PDF viewer. Download (121Mb) | Preview |
Official URL: http://webcat.warwick.ac.uk/record=b3869880
Abstract
Active matter seeks to bring a physical understanding to bear on biological systems. These systems are rendered ‘active’ by self-driven constituents which break timereversal symmetry on the local scale and induce striking non-equilibrium effects such as persistent currents. The particular focus of this thesis is active nematics, in which this activity is paired with the orientational order that characterises the nematic liquid crystalline phase. One of the signature features of passive nematics is their topological defects and these also play a defining rˆole in the dynamics of their active counterparts. The equilibrium state of a nematic is provided by harmonic functions and this thesis is a three-fold investigation of the insight these can provide into the behaviour of active nematics.
This is initiated by introducing a novel multipole approach to characterise the far-field active response to distortions of the nematic. We identify those distortions which result in actively-driven phenomena forbidden in equilibrium, such as spontaneous propulsion or rotation and also how such distortions could result from colloids or topological defect configurations.
Applying this approach to the solid angle function, appropriate to describe the distortions originating from a defect loop, reveals the part played by the loop’s geometry in its dynamics, in particular rotational effects due to non-planarity. These offer an explanation for the recent experimental observation that activity results in an uneven distribution of loop geometries.
Lastly, we use conformal mappings to investigate in two dimensions how the multipole character of a nematic may be influenced by colloidal geometry. This fulfills the initial motivation of showing how to controllably induce all the distortions we identified as producing striking active phenomenology, but also provides methods for analytic determination of the equilibrium director, applicable to a generic colloid, and shows how colloids can be designed which generate arbitrarily intricate nematic multipoles.
The results of this thesis provide a framework for understanding the basic responses of active nematics, along with the dynamics of their fundamental, topological, excitations as well as how geometry interacts with nematic order. They open up pathways to novel nematic metamaterials as well as the design of bio-inspired micromachines.
Item Type: | Thesis (PhD) | ||||
---|---|---|---|---|---|
Subjects: | Q Science > QC Physics Q Science > QD Chemistry |
||||
Library of Congress Subject Headings (LCSH): | Nematic liquid crystals, Colloidal crystals, Magnetic pole, Hydrodynamics | ||||
Official Date: | January 2022 | ||||
Dates: |
|
||||
Institution: | University of Warwick | ||||
Theses Department: | Department of Physics | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Alexander, Gareth P. | ||||
Format of File: | |||||
Extent: | vii, 171 pages : illustrations (colour) | ||||
Language: | eng |
Request changes or add full text files to a record
Repository staff actions (login required)
View Item |