# Hydrodynamically interrupted droplet growth in scalar active matter

## TL;DR

This paper investigates how negative mechanical and diffusive tensions in scalar active matter lead to unique droplet behaviors, including steady-state cycles of growth and division or arrested droplet sizes, driven by self-shearing instabilities.

## Contribution

It introduces a novel mechanism where negative mechanical tension causes a self-shearing instability, resulting in a steady cycle of droplet growth and division in active matter.

## Key findings

- Negative mechanical tension induces a self-shearing instability.
- Droplet growth is cyclically interrupted by division.
- When diffusive tension is also negative, droplet division is arrested.

## Abstract

Suspensions of spherical active particles often show microphase separation. At a continuum level, coupling their scalar density to fluid flow, there are two distinct explanations. Each involves an effective interfacial tension: the first mechanical (causing flow) and the second diffusive (causing Ostwald ripening). Here we show how the negative mechanical tension of contractile swimmers creates, via a self-shearing instability, a steady-state life cycle of droplet growth interrupted by division whose scaling behavior we predict. When the diffusive tension is also negative, this is replaced by an arrested regime (mechanistically distinct, but with similar scaling) where division of small droplets is prevented by reverse Ostwald ripening.