Field theories of soft active matter

Lead Research Organisation: University of Cambridge
Department Name: Applied Maths and Theoretical Physics


Self-propulsion is exhibited not only by micro-organisms but also by synthetic colloidal particles when immersed in a bath of fuel. These so called 'active colloids' break time-reversal symmetry locally, which means that a new formulation of statistical mechanics is needed to describe their behaviour. One approach is to construct continuum field theories for the particle density in which the symmetry is broken explicitly. This project will use numerical and analytical approaches to explore the physics of these new types of field theory and connect them to the observed dynamics of active colloids and related soft-matter systems.


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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509620/1 01/10/2016 30/09/2022
1781654 Studentship EP/N509620/1 01/10/2016 31/03/2020 Fernando Caballero Pedrero
Description This funding has been used to complete a PhD studying the different phases of systems of active matter. Active matter refers to systems made of particles than continuously consume energy and transform it into motion, something called self-propulsion. It has been shown that this self-propulsion gives rise to emergent phenomena not possible in equilibrium systems.

There are three main results coming from this work. The first result was the discovery and analysis of a mathematical description of the evolution of conserved surfaces out of equilibrium that did not exist in the literature. Our analysis shows that this model has new unknown phases that were also investigates numerically. This work will help build a more complete view about the nonequilibrium evolution of surfaces.

The second result is related to continuous descriptions of systems of self-propelled spherical particles. These systems show a particular type of phase separation induced by their self-propulsion that is not possible in equilibrium systems. We have been able to study field theories that are able to reproduce this behaviour and conclude that their phase diagram indeed shows phase transitions between uniform states and these nonequilibrium phase-separated states.

The third result has come from the study of the entropy production of these systems. This is the main observable used to quantify how much time reversibility is broken, or how far from equilibrium they are. We've found a new critical exponent that describes the surprisingly nontrivial behaviour of the entropy production of these systems, even when they are in close to equilibrium configuration in which no entropy production would be expected at large length scales. We found instead that entropy production still exists in equilibrium fixed points and can even be diverging if the system lies close enough to these points.
Exploitation Route Given the nature of fundamental research, the outcomes of this funding will mostly be applied and expanded by other researchers in similar fields, in order to further understand and analyse the outcomes of this work and the properties of these systems. Alternatively, active systems are increasingly becoming part of various potential manufacturing processes for which properly understanding their behaviour and phase diagrams would be vital.
Sectors Chemicals,Other