Pressure, surface tension and curvature in active systems: A touch of equilibrium

Abstract

We explore the pressure of active particles on curved surfaces and its relation to other interfacial properties. We use both direct simulations of the active systems as well as simulations of an equilibrium system with effective (pair) interactions designed to capture the effects of activity. Comparing the active and effective passive systems in terms of their bulk pressure, we elaborate that the most useful theoretical route to this quantity is via the density profile at a flat wall. This is corroborated by extending the study to curved surfaces and establishing a connection to the particle adsorption and integrated surface excess pressure (surface tension). In the ideal-gas limit, the effect of curvature on the mechanical properties can be calculated analytically in the passive system with effective interactions, and shows good (but not exact) agreement with simulations of the active models. It turns out that even the linear correction to the pressure is model specific and equals the planar adsorption in each case, which means that a known equilibrium sum rule can be extended to a regime at small but nonzero activity. In turn, the relation between the planar adsorption and the surface tension is reminiscent of the Gibbs adsorption theorem at an effective temperature. At finite densities, where particle interactions play a role, the presented effective-potential approximation captures the effect of density on the dependence of the pressure on curvature.

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• The Parental Active Model: a unifying stochastic description of self-propulsion
• Collective forces in scalar active matter
• A comparative study between two models of active cluster-crystals
• Dynamics of active particles with space-dependent swim velocity
• Dynamics of active particles with translational and rotational inertia
• Coexistence of active Brownian discs: Van der Waals theory and analytical results
• Force density functional theory in- and out-of-equilibrium
• Designing, Synthesizing and Modeling Active Fluids
• Tuning Nonequilibrium Phase Transitions with Inertia
• Density and Polarization of Active Brownian Particles in Curved Activity Landscapes
• Mechanical pressure and work cycle of confined active Brownian particles
• Dynamic Overlap Concentration Scale of Active Colloids
• Active Young-Dupré Equation: How Self-organized Currents Stabilize Partial Wetting
• On the effect of boundaries on noninteracting weakly active particles in different geometries
• Confined active particles with spatially dependent Lorentz force: an odd twist to the "best Fokker-Planck approximation"
• Correlated escape of active particles across a potential barrier