Hydrodynamic Instabilities, Pattern Formation and Topology in Active

Lead Research Organisation: University of Warwick
Department Name: Physics

Abstract

Active liquid crystals have come to represent an archetype for active matter, offering a framework for organising ideas about biological processes and biologically inspired materials, ranging from bacterial swarms and growing colonies to the cell cytoskeleton. Certain generic traits for active materials, such as spontaneous flows, hydrodynamic instabilities and active turbulence, have been identified using the phenomenology of liquid crystals. This area continues to provide fundamental questions in non-equilibrium physics, with potentially widespread applications across biology. For the most part, existing work has focused on nematic or polar phases, and also largely on a two-dimensional characterisation. Chirality is ubiquitous in nature, appearing both in biological structures and in suspen- sions of the filaments and biopolymers that they are made from. For instance, DNA forms chiral liquid crystalline phases in solution. However, the effects of active stresses on chiral materials and structures have so far not been studied.
This project will develop the characterisation and understanding of chiral active materials using the framework and phenomenology of cholesteric liquid crystals. We will extend and continue initial work in my group on the fundamental hydrodynamic instabilities in active cholesterics, in particular to a full three-dimensional analysis, to account for the influence of boundary conditions, or confinement, and to study the stability of different passive cholesteric textures. For instance, it would be natural to determine the morphology of thin films on substrates, or of active cholesteric droplets

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509796/1 01/10/2016 30/09/2021
1917431 Studentship EP/N509796/1 02/10/2017 30/06/2021 Alexander James Houston
 
Description We used a liquid-crystalline model to study the behaviour of a fluid comprised of components which are active, meaning that they can inject energy into the system, and which have a preference for orientational ordering. Such active liquid crystals have implications both for living systems and biologically-inspired materials and their dynamics is governed by a coupling between the local alignment of the components and the fluid flows. We constructed response functions, analogous to those of equilibrium statistical mechanics, for the fluid flow. These connect to the established fluid instabilities present in these systems and allow us to determine the flow caused by a generic distortion in the ordering. Additionally we calculated the net force and torque on a region of the material, which allows the design of colloidal inclusions which would have a prescribed steady linear or rotational motion. This relates to the area of active ratchets, namely extracting directed motion from a non-equilibrium system. Alternatively if the colloid was pinned such that it was not free to move it would pump or stir the surrounding fluid. The flow field around propelled colloids in these systems has a different form from that of standard models of bacterial swimmers and particularly the fluid stirring that can be induced is more long-ranged than that typically found.
Exploitation Route The work described above can be expanded academically by for example considering the interactions between multiple colloids or changing the underlying ordering of the material to be chiral. Beyond this it has the potential to be used to design methods of transport, separation and stirring in biological fluids. Such control would be of benefit in both industry and medicine.
Sectors Manufacturing, including Industrial Biotechology,Pharmaceuticals and Medical Biotechnology