Autophoretic locomotion from geometric asymmetry

TL;DR

This paper demonstrates that geometric asymmetries alone can generate self-phoretic swimming in small-scale devices, eliminating the need for chemical patterning by inducing chemical gradients through shape differences.

Contribution

It introduces a novel approach showing that geometric asymmetry can induce self-propulsion in chemically homogeneous swimmers, supported by exact and asymptotic calculations.

Findings

Geometric asymmetries can produce significant propulsion speeds.

Shape deformations induce chemical gradients sufficient for swimming.

Chemical patterning is unnecessary for self-phoretic locomotion.

Abstract

Among the few methods which have been proposed to create small-scale swimmers, those relying on self-phoretic mechanisms present an interesting design challenge in that chemical gradients are required to generate net propulsion. Building on recent work, we propose that asymmetries in geometry are sufficient to induce chemical gradients and swimming. We illustrate this idea using two different calculations. We first calculate exactly the self-propulsion speed of a system composed of two spheres of unequal sizes but identically chemically homogeneous. We then consider arbitrary, small-amplitude, shape deformations of a chemically-homogeneous sphere, and calculate asymptotically the self-propulsion velocity induced by the shape asymmetries. Our results demonstrate how geometric asymmetries can be tuned to induce large locomotion speeds without the need of chemical patterning.