Explosive Marangoni Propulsion Allows Water Skaters and Robots to Traverse Fast Flows

Microvelia Water Skaters are well known for their limited limb-based propulsion, which constrains their ability to escape predators on water surface. Remarkably, when disturbed, these millimeter-sized insects release surfactants onto the water, creating a surface tension gradient that enables a faster escape than they can achieve by skating alone. Counterintuitively, these millimeter-sized insects inhabit and actively hunt trapped prey in fast flowing streams, where the flow speeds exceed their natural skating capabilities. Here, we experimentally show that Microvelia water skaters moving in rapid flows—beyond their limb-based propulsion limits— use rapid Marangoni propulsion burst, followed by limb-based strokes, to effectively move upstream. We present a proof-of-concept interfacial robot capable of propelling on moving flows, which employs rapid marangoni-driven propulsion to overcome intense currents. Our results can inform the design of interfacial micro-vehicles capable of effectively moving on streams by harnessing the Marangoni effect.