Why superhydrophobicity is crucial for a water-jumping microrobot? Experimental and theoretical investigations.

This study reported for the first time a novel microrobot that could continuously jump on the water surface without sinking, imitating the excellent aquatic locomotive behaviors of a water strider. The robot consisted of three supporting legs and two actuating legs made from superhydrophobic nickel foam and a driving system that included a miniature direct-current motor and a reduction gear unit. In spite of weighing 11 g, the microrobot jumped 14 cm high and 35 cm long at each leap. In order to better understand the jumping mechanism on the water surface, the variation of forces exerted on the supporting legs was carefully analyzed and calculated based on numerical models and computational simulations. Results demonstrated that superhydrophobicity was crucial for increasing the upward force of the supporting legs and reducing the energy consumption in the process of jumping. Although bionic microrobots mimicking the horizontal skating motions of aquatic insects have been fabricated in the past years, few studies reported a miniature robot capable of continuously jumping on the water surface as agile as a real water strider. Therefore, the present finding not only offers a possibility for vividly imitating and better understanding the amazing water-jumping capability of aquatic insects but also extends the application of porous and superhydrophobic materials to advanced robotic systems.