Speaker
Description
Active (or self-propelled) particles constantly consume internal energy to move in the environment, constantly preventing the system to reach equilibrium. This allows for a variety of fascinating phenomena to appear, such as the phase separation into a dense and a dilute phase in the complete absence of attractive interactions, known as motility-induced phase separation (MIPS) [1]. Although MIPS retains many aspects of gas-liquid demixing at equilibrium, its inherent non-equilibrium origin leads to a new physical phenomenology. Here we illustrate some of the peculiar features of the MIPS dynamics in numerical simulations of 2d self-propelled disks [2].
We show the presence of another ordering mechanism beyond the equilibrium-like phase separation, namely the micro-phase separation of hexatic domains and vapor bubbles within dense clusters of particles [3]. We studied the steady-state size of these structures and found that it can be directly controlled by tuning the self-propulsion strength of the individual particles.
We also provide a detailed analysis of the dynamics of individual clusters during the phase separation process [4]. We show that active clusters have diffusive behavior that is enhanced by the self-propulsion strength and that the diffusion coefficient depends in a non-trivial way on the total mass of the cluster, which is a pure non-equilibrium effect induced by self-propulsion. Finally, we show that cluster diffusion controls the phase separation process of the system and leads to the formation of larger structures characterized by a fractal geometry.
References
[1] Cates M., Tailleur J. Annu. Rev. Condens. Matter Phys. (2015)
[2] Digregorio P., Levis D., Suma A., Cugliandolo L.F., Gonnella G., Pagonabarraga I. Phys. Rev. Lett. (2018).
[3] Caporusso C.B., Digregorio P., Levis D., Cugliandolo L.F., Gonnella G. Phys. Rev. Lett. (2020)
[4] Caporusso C.B., Digregorio P., Cugliandolo L.F., Gonnella G., Levis D., Suma A., arXiv:2211.12361
