Wetting by active fluids
arXiv:2405.20651 · doi:10.1038/s41567-026-03208-4
Abstract
The Young-Dupré equation is a cornerstone of the theory of capillary and wetting phenomena that governs the shape of droplets adsorbed on surfaces in equilibrium. But many living and synthetic materials, such as swarming bacteria and active colloids, are composed of self-propelled particles that are inherently out of thermal equilibrium. The description of the wetting of surfaces by such active fluids thus requires a new framework. Here, we develop an analogue to the Young-Dupré equation for systems made of self-propelled particles. A key step is to define the liquid-gas surface tension of active fluids as the force exerted along the interface, which we show from first principles to be negative, even when active materials separate into stable liquid and gas phases. The active Young-Dupré equation explains why partial wetting appears in simulations where the surface tensions do not balance and reveals the underlying feedback mechanism: the interface is stable only because of steady flows, which are themselves generated by the parity-symmetry-breaking interface. Unlike in passive fluids, where the droplets are scale-free, this feedback loop selects the sizes and shapes of adsorbed droplets in active materials. Our results outline a framework for understanding how active matter wets surfaces.
51 pages, 5+13 figures
References in corpus (39)
- Motility-Induced Phase Separation
- Dynamical clustering and phase separation in suspensions of self-propelled colloidal particles
- Athermal Phase Separation of Self-Propelled Particles with no Alignment
- Emergence of macroscopic directed motion in populations of motile colloids
- Onset of collective and cohesive motion
- Statistical mechanics for natural flocks of birds
- Genetic drift at expanding frontiers promotes gene segregation
- Sedimentation of active colloidal suspensions
- Pressure is not a state function for generic active fluids
- Pressure and Phase Equilibria in Interacting Active Brownian Spheres
- A self-propelled particle in an external potential: is there an effective temperature?
- Active wetting of epithelial tissues
- Negative interfacial tension in phase-separated active suspensions
- Generalized thermodynamics of Motility-Induced Phase Separation: Phase equilibria, Laplace pressure, and change of ensembles
- Casimir Effect in Active Matter Systems
- Dynamics of active liquid interfaces
- Active vs. Passive Hard Disks Against a Membrane : Mechanical Pressure and Instability
- Mechanical pressure and momentum conservation in dry active matter
- Microscopic Origins of the Swim Pressure and the Anomalous Surface Tension of Active Matter
- A Drop of Active Matter
- Capillary interfacial tension in active phase separation
- Curvature-dependent tension and tangential flows at the interface of motility-induced phases
- Non-Equilibrium Surface Tension of the Vapour-Liquid Interface of Active Lennard-Jones Particles
- Non-negative Interfacial Tension in Phase-Separated Active Brownian Particles
- Sedimentation of self-propelled Janus colloids: polarization and pressure
- Collective forces in scalar active matter
- Fluctuation-induced phase separation in metric and topological models of collective motion
- Active phase separation: new phenomenology from non-equilibrium physics
- Classical Nucleation Theory for Active Fluid Phase Separation
- Local stress and pressure in an inhomogeneous system of spherical active Brownian particles
- Activity-suppressed phase separation
- Surface Tensions between Active Fluids and Solid Interfaces: bare vs dressed
- Pressure, surface tension and curvature in active systems: A touch of equilibrium
- Inclusions, Boundaries and Disorder in Scalar Active Matter
- Capillary action in scalar active matter
- Wetting dynamics by mixtures of fast and slow self-propelled particles
- Theory of Capillary Tension and Interfacial Dynamics of Motility-Induced Phases
- The Mechanics of Nucleation and Growth and the Surface Tensions of Active Matter
- Stationary particle currents in sedimenting active matter wetting a wall
Cited by in corpus (4)
- Interfacial and density fluctuations in a lattice model of motility-induced phase separation
- Active wetting transitions induced by rotational noise at solid interfaces
- What is active wetting?
- Non-equilibrium pathways between cluster morphologies in active phase separation: necking, rupture and cavitation