What tiny surfing robots teach us about surface tension — ScienceDaily


Spend an afternoon by a creek in the woods, and you’re likely to notice water striders — long-legged insects that dimple the surface of the water as they skate across. Or, dip one side of a toothpick in dish detergent before placing it in a bowl of water, and impress your grade schooler as the toothpick gently starts to move itself across the surface.

Both situations illustrate the concepts of surface tension and propulsion velocity. At Michigan Technological University, mechanical engineer Hassan Masoud and PhD student Saeed Jafari Kang have applied the lessons of the water strider and the soapy toothpick to develop an understanding of chemical manipulation of surface tension.

Their vehicle? Tiny surfing robots.

“During the past few decades, there have been many efforts to fabricate miniature robots, especially swimming robots,” said Masoud, an assistant professor in the mechanical engineering-engineering mechanics department. “Much less work has been done on tiny robots capable of surfing at the interface of water and air, what we call liquid interfaces, where very few robots are capable of propelling themselves.”

Beyond the obvious implications for future Lucasfilm droids designed for ocean planets (C-H2O), what are the practical applications of surfing robots?

“Understanding these mechanisms could help us understand colonization of bacteria in a body,” Masoud said. “The surfing robots could be used in biomedical applications for surgery. We are unraveling the potential of these systems.”

Hunting for Answers and the Marangoni Effect

During his doctoral studies and postdoc appointment, Masoud conducted research to understand the hydrodynamics of synthetic microrobots and the mechanisms by which they move through fluid. While helping a colleague with an experiment, Masoud made an observation he couldn’t explain. An aha! moment came shortly thereafter.

“During a conversation with a physicist, it occurred to me that what we had observed