Selecting the swimming mechanisms of colloidal particles: bubble propulsion versus self-diffusiophoresis.

Bubble propulsion and self-diffusiophoresis are two common mechanisms that can drive autonomous motion of microparticles in hydrogen peroxide. Although microtubular particles, when coated with platinum in their interior concave surfaces, can propel due to the formation and release of bubbles from one end, the convex Janus particles usually do not generate any visible bubble. They move primarily due to the self-diffusiophoresis. Coincidentally, the platinum films on those particles were typically coated by physical evaporation. In this paper, we use a simple chemical deposition method to make platinum-polystyrene Janus dimers. Surprisingly, those particles are propelled by periodic growth and collapse of bubbles on the platinum-coated lobes. We find that both high catalytic activity and rough surface are necessary to change the propulsion mode from self-diffusiophoresis to bubble propulsion. Our Janus dimers, with combined geometric and interfacial anisotropy, also exhibit distinctive motions at the respective stages of bubble growth and collapse, which differ by 5-6 orders of magnitude in time. Our study not only provides insight into the link between self-diffusiophoresis and bubble propulsion but also reveals the intriguing impacts of the combined geometric and interfacial anisotropy on self-propulsion of particles.