Designing phoretic micro- and nano-swimmers

TL;DR

This paper develops a theoretical framework to understand and optimize the design of phoretic micro- and nano-swimmers, emphasizing the importance of symmetry breaking and surface properties for efficient swimming.

Contribution

It provides a general quantification method for swimmer efficiency based on shape, surface activity, and mobility, applicable to arbitrary geometries and patterns.

Findings

Swimming requires symmetry breaking in activity or mobility patterns.

Swimming velocity is independent of the swimmer's size for fixed surface properties.

The framework guides optimal design of phoretic swimmers.

Abstract

Small objects can swim by generating around them fields or gradients which in turn induce fluid motion past their surface by phoretic surface effects. We quantify for arbitrary swimmer shapes and surface patterns, how efficient swimming requires both surface ``activity'' to generate the fields, and surface ``phoretic mobility.'' We show in particular that (i) swimming requires symmetry breaking in either or both of the patterns of "activity" and ``mobility,'' and (ii) for a given geometrical shape and surface pattern, the swimming velocity is size-independent. In addition, for given available surface properties, our calculation framework provides a guide for optimizing the design of swimmers.