Slip and distance effects on the self-propulsion of catalytic microswimmers close to a wall

Catalytic microswimmers are typically found self-propelling parallel to substrates. Although experimental observations have so far hinted at non-negligible substrate effects on the swimmer velocity, a quantitative examination of the effect of the substrate is still lacking.
In this talk, we will present quantitative measurements of the effect of the substrate on the velocity of Pt-coated model microswimmers. We will show that under otherwise fixed conditions the velocity depends on the substrate wetting angle, which in turn relates to the associated hydrodynamic slip length of the substrate. We will further demonstrate that our hypothesis on slip dependent velocities is not only supported by qualitative and scaling arguments, but also by our measurements on swimmer-wall separation distance.
Our findings provide further understanding on the swimming behavior of synthetic microswimmers. Such understanding is desirable for future applications that may require microscopic devices to self-propel in liquid environments in confinement and along boundaries.