The phase behaviour of active colloidal rollers

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


Active matter systems are those able to continuously consume energy from the environment in order to drive themselves out-of-equilibrium. This leads to fasci- nating behaviours not attainable at thermal equilibrium. Some of the hallmarks
of such systems are the self-propulsion of individuals, and the emergence of collective phenomena, such as swarming, flocking, clustering, and phase separation in the absence of attractive forces. Moreover, such phenomena occurs in a wide range of living systems at different length scales, from the cell cytoskeleton, tissues, and bacterial colonies to larger scales such as fish schools and bird flocks.
Artificial active materials, consisting of active particles, vibrated grains, or even synthetically modified living systems, provide suitable model systems to test the behavior of active matter, and to investigate the physical principles behind. In this sense, much of the active behaviours rely upon the interactions in the system, such as the alignment interaction that promote coherent flows, as in flocks. Thus, we describe a population of interacting and motile colloidal particles, that exhibit phase transitions between passive and active states, i.e. swarms and polar flocks. Our system displays a rich and exotic phase behavior, including passive and motile crystallites, an active gas, and polar bands. We find that at low motility, competing passive and active interactions leads to the melting-like and behavior of active crystallites. On increasing the motility, the role of the interactions is reversed, and promotes the onset of flocking.
Date of Award30 Jul 2020
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorJeroen S Van Duijneveldt (Supervisor) & Cp Royall (Supervisor)

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