Mobile robots combine sensory information with mechanical actuation to move autonomously through complex environments and perform specific tasks (e.g., a robot vacuum cleaner). The miniaturization of such robots to the size of living cells (ca. 2-40 mm) is actively pursued for applications in biomedicine, materials science, and environmental sustainability. In pursuit of these “microrobots”, we seek to understand the many mechanisms underlying the self-propulsion of colloidal particles through viscous fluids. Building on this understanding, we seek to design active particles capable of autonomous behaviors such as navigation of structured environments. In this talk, I discuss two recent efforts – on Quincke oscillators and magnetic topotaxis, respectively – that highlight these complementary aims to understand and design active colloids. In part one, I explain how static electric fields drive the oscillatory motion of micron-scale particles commensurate with the thickness of a field-induced boundary layer in nonpolar electrolytes. In part two, I describe how spatially uniform, time-periodic magnetic fields can be designed to power and direct the migration of ferromagnetic spheres up local gradients in surface topography.
