# Slip length dependent propulsion speed of catalytic colloidal swimmers near walls

## TL;DR

This study experimentally demonstrates that the propulsion speed of catalytic colloidal swimmers near surfaces depends on the substrate's slip length, which influences their velocity through osmotic coupling effects.

## Contribution

It reveals a quantitative relationship between swimmer velocity and substrate slip length, highlighting the role of hydrodynamic slip in microswimmer propulsion.

## Key findings

- Swimmer velocity scales with contact angle and slip length.
- Velocity depends on osmotic coupling between swimmer and substrate.
- Hydrodynamic slip significantly affects catalytic swimmer propulsion.

## Abstract

Catalytic colloidal swimmers that propel due to self-generated fluid flows exhibit strong affinity for surfaces. We here report experimental measurements of significantly different velocities of such microswimmers in the vicinity of substrates made from different materials. We find that velocities scale with the solution contact angle $\theta$ on the substrate, which in turn relates to the associated hydrodynamic substrate slip length, as $V\propto(\cos\theta+1)^{-3/2}$. We show that such dependence can be attributed to osmotic coupling between swimmers and substrate. Our work points out that hydrodynamic slip at the wall, though often unconsidered, can significantly impact the self-propulsion of catalytic swimmers.