Photochemically Powered AgCl Janus Micromotors as\na Model System to Understand Ionic Self-Diffusiophoresis

Abstract

Micromotors are an\nemerging class of micromachines that could find\npotential applications in biomedicine, environmental remediation,\nand microscale self-assembly. Understanding their propulsion mechanisms\nholds the key to their future development. This is especially true\nfor a popular category of micromotors that are driven by asymmetric\nsurface photochemical reactions. Many of these micromotors release\nionic species and are propelled via a mechanism termed “ionic\nself-diffusiophoresis”. However, exactly how it operates remains\nvague. To address this fundamental yet important issue, we have developed\na dielectric-AgCl Janus micromotor that clearly moves away from the\nAgCl side when exposed to UV or strong visible light. Taking advantage\nof numerical simulations and acoustic levitation techniques, we have\nprovided tentative explanations for its speed decay over time as well\nas its directionality. In addition, photoactive AgCl micromotors demonstrate\ninteresting gravitactic behaviors that hint at three-dimensional transport\nor sensing applications. The current work presents a well-controlled\nand easily fabricated model system to understand chemically powered\nmicromotors, highlighting the usefulness of acoustic levitation for\nstudying active matter free from the effect of boundaries.