Spontaneous motion and deformation of a self-propelled droplet

TL;DR

This paper derives the equations governing the motion and shape changes of a chemically driven self-propelled droplet, revealing how chemical-flow coupling causes spontaneous motion and shape deformation, with the droplet elongating perpendicular to its motion.

Contribution

It introduces a theoretical framework linking chemical reactions to droplet motion and shape deformation, highlighting the instability leading to spontaneous propulsion.

Findings

Droplet becomes elongated perpendicular to motion

Self-propelled droplet characterized as a pusher

Chemical reaction induces flow and shape instability

Abstract

The time evolution equation of motion and shape are derived for a self-propelled droplet driven by a chemical reaction. The coupling between the chemical reaction and motion makes an inhomogeneous concentration distribution as well as a surrounding flow leading to the instability of a stationary state. The instability results in spontaneous motion by which the shape of the droplet deforms from a sphere. We found that the self-propelled droplet is elongated perpendicular to the direction of motion and is characterized as a pusher.