Partial and complete wetting of droplets of active Brownian particles

F Turci and RL Jack and NB Wilding, SOFT MATTER, 20, 2060-2074 (2024).

DOI: 10.1039/d3sm01493b

We study wetting droplets formed of active Brownian particles in contact with a repulsive potential barrier, in a wedge geometry. Our numerical results demonstrate a transition between partially wet and completely wet states, as a function of the barrier height, analogous to the corresponding surface phase transition in passive fluids. We analyse partially wet configurations characterised by a nonzero contact angle theta between the droplet surface and the barrier including the average density profile and its fluctuations. These findings are compared with two equilibrium systems: a Lennard-Jones fluid and a simple contour model for a liquid-vapour interface. We locate the wetting transition where cos(theta) = 1, and the neutral state where cos(theta) = 0. We discuss the implications of these results for possible definitions of surface tensions in active fluids. Active droplets exhibit behavior akin to equilibrium wetting despite complex flows.

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