The dynamics of chemically propelled dimer motors on a pinning substrate

The dynamics of self-propelled micro-motors, in a thin fluid film containing an attractive substrate, is investigated by means of a particle-based simulation. A chemically powered sphere dimer, consisting of a catalytic and a noncatalytic sphere, may be captured by a trap on the substrate and consequently rotates around the trap center. A pair of trapped dimers spontaneously forms various configurations, including anti-parallel aligned doublets and head-to-tail rotating doublets. Small traps randomly distributed on the substrate are capable of pinning the dimers. The diffusion coefficient decreases with increasing pinning force or the pinning density, and it falls quickly at a certain critical pinning force beyond which the dimer motor is pinned completely. It is found that the pin array on the substrate gives rise to the formation of clusters of dimers and the underlying mechanism is discussed.