# Capillary action in scalar active matter

## TL;DR

This paper investigates how scalar active matter can exhibit capillary action phenomena similar to classical fluids, driven by emergent effective attractions from particle interactions, with simulations revealing relationships between active sedimentation length and capillary rise.

## Contribution

It introduces a minimal model for scalar active matter demonstrating emergent capillarity due to purely repulsive interactions, a phenomenon not observed in passive fluids.

## Key findings

- Capillary rise is proportional to active sedimentation length $\\lambda$.
- Wetting height grows superlinearly with $\\lambda$.
- Imbibition height scales with sedimentation length and packing fraction.

## Abstract

We study the capacity of active matter to rise in thin tubes against gravity and other related phenomena, like, wetting of vertical plates and spontaneous imbibition, where a wetting liquid is drawn into a porous medium. This capillary action or capillarity is well known in classical fluids and originates from attractive interactions between the liquid molecules and the container walls, and from the attraction of the liquid molecules among each other. We observe capillarity in a minimal model for scalar active matter with purely repulsive interactions, where an effective attraction emerges due to slowdown during collisions between active particles and between active particles and walls. Simulations indicate that the capillary rise in thin tubes is approximately proportional to the active sedimentation length $\lambda$ and that the wetting height of a vertical plate grows superlinear with $\lambda$. In a disordered porous medium the imbibition height scales as $\langle h\rangle\propto\lambda\phi_m$, where $\phi_m$ is its packing fraction.