Non-equilibrium pairwise forces in active matter
File(s)
Author(s)
Alston, Henry
Type
Thesis
Abstract
Life requires a departure from thermodynamic equilibrium. This departure allows living systems to exhibit structures and dynamics that are inimitable in passive systems. The construction of non-equilibrium statistical mechanics techniques allows for a quantitative description of these emergent phenomena. Significant progress has been made on this front by isolating microscopic dissipative processes in both single- and many-particle systems, such as particle self-propulsion, and characterising the resulting non-equilibrium physics by extending and adapting our existing analytic framework. In nature, complexity is ubiquitous: emergent phenomena in biology are the result of many interacting dissipative processes. Therefore, understanding the consequences of each process itself is a significant and crucial step towards constructing a quantitative theory for the physics of living matter. In this thesis, I address the role of non-equilibrium pairwise forces: pairwise interactions that can maintain a system out of thermodynamic equilibrium. Alongside the broad biological relevance (modelling e.g. pili-mediated interactions between bacteria, chemotactic interactions in living and synthetic systems, and stochastic binding-unbinding interactions enabled by e.g. ligand-receptor contacts), this class of active system presents a natural extension to those where activity is introduced at the single-particle level (through e.g. self-propulsion), which have been the central focus of the ongoing research in the field. We formalise the study of non-equilibrium pairwise forces by identifying three exhaustive characteristics: fluctuating, non-reciprocal and non-conserved forces. The remainder of the thesis is then dedicated to studying the non-equilibrium structures and dynamics that arise due to the presence forces. We show that this class of active system captures a striking range of collective phenomena: non-equilibrium phase separation, heightened material response and travelling macroscopic phases driven by a breaking of PT-symmetry. By widening the focus beyond motile active matter, this work contributes significantly towards establishing a comprehensive theory governing the diverse processes that bring matter to life.
Version
Open Access
Date Issued
2024-03-27
Date Awarded
01/07/2024
License URL
Advisor
Bertrand, Thibault
Parry, Andrew
Sponsor
Imperial College London
Publisher Department
Mathematics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)