Ladderlike Tapered Pillars Enabling Spontaneous and Consecutive Liquid Transport

Directional liquid transport has significant domestic and industrial applications. Tapered objects have theoretically and experimentally been demonstrated to have the ability to spontaneously transport liquids. However, the transporting distance is limited, and consecutively and spontaneously transporting liquids has always been a challenge. In this work we proposed to exploit ladderlike tapered pillars, which are inspired by relay races, to increase the transport distance. These pillars were designed using a developed numerical model and fabricated by a novel alternating etching and coating method followed by wettability enhancement. We demonstrated through experiments that the resulting pillars could consecutively and spontaneously transport a liquid droplet at an average velocity of 0.139 m/s with a maximum acceleration of 5 g. The optimum window of the tilt angle range (0°-25°), contact angle (50°), and the chemical modification time (5 min) were obtained. Such ladderlike tapered pillars are able to improve the water-collection efficiency. These results may provide a new and systematic way to design and fabricate materials and structures for directional liquid transport.