Abstract: This talk will describe recent simulation studies of non-equilibrium analogues of wetting transitions in a minimal model of active particles in contact with a purely repulsive potential barrier that mimics a thin, porous membrane. Under conditions of bulk motility-induced phase separation into a dense and less dense fluid phase, the barrier height epsilon controls the affinity of the dense phase for the barrier region. As epsilon is varied, a symmetry breaking occurs with regard to the location of the dense phase relative to the barrier. This is argued to signal a surface phase transition from a wet to a partially wet state.

To shed further light on the phenomenology, we consider the behaviour of wetting droplets formed of active particles in contact with a wedged shaped repulsive potential barrier that serves to confine the droplet. We analyse partially wet configurations characterised by a nonzero contact angle theta between the droplet surface and the barrier and determine the average density profile and its fluctuations. Our results accord qualitatively with the behaviour of a passive (Lennard-Jones) fluid and a simple contour model for a liquid-vapour interface in the same geometry, thereby confirming the presence of a wetting transition. Our results have implications for possible definitions of surface tensions in active fluids.

1. F. Turci and N.B. Wilding, Phys. Rev. Lett. 127, 238002 (2021)
2. F. Turci, R.L. Jack, and N.B. Wilding, https://arxiv.org/abs/2310.07531