Viscous Marangoni propulsion

TL;DR

This paper develops a mathematical model for viscous Marangoni propulsion of a surfactant-covered disk at a liquid surface, providing analytical solutions for the flow and surfactant fields and quantifying propulsion speed.

Contribution

It introduces an analytical model for viscous Marangoni propulsion of a rigid disk, including surfactant, velocity, and pressure fields, and evaluates the propulsion speed.

Findings

Neglecting Marangoni stress overestimates propulsion speed by 50%.

Analytical solutions derived for surfactant, velocity, and pressure fields.

Model applicable in low Capillary, Peclet, and Reynolds number regimes.

Abstract

Marangoni propulsion is a form of locomotion wherein an asymmetric release of surfactant by a body located at the surface of a liquid leads to its directed motion. We present in this paper a mathematical model for Marangoni propulsion in the viscous regime. We consider the case of a thin rigid circular disk placed at the surface of a viscous fluid and whose perimeter has a prescribed concentration of an insoluble surfactant, to which the rest of its surface is impenetrable. Assuming a linearized equation of state between surface tension and surfactant concentration, we derive analytically the surfactant, velocity and pressure fields in the asymptotic limit of low Capillary, Peclet and Reynolds numbers. We then exploit these results to calculate the Marangoni propulsion speed of the disk. Neglecting the stress contribution from Marangoni flows is seen to over-predict the propulsion speed by 50%.