Heterogeneous Active Matter in Confined Spaces: theory and simulations

Abstract

In this project I studied the collective behaviour of dense swarms of rodshaped particles with heterogeneous properties. I consider confined systems as well as unbounded domains with periodic boundary conditions and (ir-)regular obstacles of various nature. All results that I provide are based on my own molecular dynamics based code and can be used in various cases of collective behaviour such as bacterial motion, artificial active particles (swarm robotics), animal interaction, for example, flocking of birds or schooling of fish or even crowd control. Ch. 1 provides an introduction to active matter. I give a brief explanation of this phenomena and provide various examples that naturally arise in living and artificial systems. I also discuss various models of active matter, including the one that is used in the following chapters, and their pros and cons. In Ch. 2, I thoroughly discuss the model for heterogeneous active matter I present it as an extension for an existing method to simulate homogeneous self-motile particles. I also provide the numerical background for the simulation code as well as some solutions to particular problems that come out in computer simulations of confined heterogeneous active matter. The results will be submitted in the form of a computational package in the near future. Ch. 3 introduces self-propelled rods moving in a periodic (quasi-) 2D channel. I start with conventional active systems where all particles are identical. I compare them to systems where rods have heterogeneous properties i.e. every active particle has its own hardness and/or self-propellant force picked from a given distribution. I study how this introduced heterogeneity affects the resulting distribution of active matter in the confinement comparing to homogeneous systems. The results of this study have been published in Physical Review E [1]. In Ch. 4, the statistical properties of the homogeneous active matter are given using the mean square displacement and the so-called giant density fluctuations metric. This part of the thesis shows how a variety of behaviours emerges in confined systems of self-motile rods. The main finding here is that all patterns of motion observed in such systems can be arranged according to the corresponding values of the metrics above. Conclusions and the perspective of all unanswered questions are given in Ch. 5. Whereas the area of active matter has been developed for more than 20 years, many problems still have to be solved. This chapter provides a potential direction of further active matter development as well as a summary of the thesis.

Date of Award	2020
Original language	English
Awarding Institution	Aberystwyth University
Supervisor	Martin Swain (Supervisor) & Adil Mughal (Supervisor)