Limiting propulsion of ionic microswimmers

Catalytic Janus swimmers self-propel in electrolyte solutions, thanks to inhomogeneous release of active ions from their surface. Here, we consider the experimentally relevant cases of particles, which eject only one type of ions (referred to as swimmers of type I) or equal fluxes of cations and anions (termed swimmers of type II). Our main focus is on the impact of passive ions of the added salt on the self-propulsion. In the limit of a thin electrostatic diffuse layer, we derive a nonlinear outer solution for the electric field and concentrations of active and passive ionic species. We show that both the maximum ion flux and propulsion velocity are constrained for swimmers of type I, but they remain unaffected for particles of type II.

Automated summary

Catalytic Janus swimmers can propel themselves in electrolyte solutions by releasing active ions from their surface. We investigated the effect of passive ions from added salt on the self-propulsion of two types of swimmers: those that release only one type of ion (type I) and those that release equal amounts of cations and anions (type II). Our results showed that the maximum ion flux and propulsion velocity are constrained for type I swimmers, but remain unaffected for type II particles.