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## UMR 5672

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# Cluster phases and bubbly phase separation in active fluids

Cesare Nardini (CEA Saclay)
When Oct 16, 2018 from 02:00 to 03:00 room 116 Cesare Nardini vCal iCal
It is known that purely repulsive self-propelled colloids can undergo bulk liquid-vapor phase separation. In experiments and large scale simulations, however, more complex steady states are often seen, comprising a dynamic population of dense clusters in a sea of vapor, or dilute bubbles in a liquid.

In this talk, we show that these microphase separated states should emerge generically in active matter, without any need to invoke system-specific details, describe them at coarse-grained level and analyse the transition between bulk phase separation and microphase separation.

We achieve these results by extending the $\phi^4$ field theory of passive phase separation to allow for all local currents that break detailed balance at leading order in the gradient expansion. Microphase separation is explained by the fact that the classical Ostwald process, that would normally drive bulk phase separation to completion, can be reversed due to the presence of mesoscopic active currents.

We conclude the talk discussing the transition to microphase separation beyond mean-field by showing, using dynamical Renormalization Group theory, that it belongs to a new non-equilibrium universality class.

The talk is based on:
- E. Tjhung, CN, M.E. Cates, arXiv:1801.07687, accepted in PRX
- F. Caballero, CN, M.E. Cates, in preparation