Power-law intermittency in the active motion of colloidal swimmers

Colloidal microswimmers have received broad interest, serving as archetypical active fluid system, and as models for their biological conterparts. While the principles of their motion has been vastly explored and the velocity dependence on system parameters studied in detail, the nature of their time-dependent motion has been less addressed.

Here, by studying in detail the time-dependent propagation of colloidal swimmers, we find remarkable power-law intermittency of the swimming velocity magnitude. This intermittency is robust across different swimmer types, and appears to be a generic property of the swimming mechanism itself. We model the swimmer motion by an interplay of active force, set by the chemical or fuel gradient, and hydrodynamic drag, set by the wetting properties of the substrate, which we assume to fluctuate due to surface heterogeneities and fluctuations in the particle's height above the substrate. We show that the model describes the power-law velocity distributions very well, allowing insight into the underlying mechanism. The generic feature behind the power-law distributions is highlighted by the collapse of all colloidal swimmer data in a single master curve. These results suggest that many more swimmers, whose active motion is driven by chemical or nutrient gradients near a wall, both synthetic and biological, exhibit similar robust intermittent motion, governed by the same fundamental principles.