Janus Spherical Robot With Multiple Wettabilities for Droplet/ Bubble Manipulation

Abstract

The flexible manipulation and directional transport of fluids, including droplets and bubbles, are foundational to numerous applications. Fluid manipulation based on external field stimulation and fixed structures has a wide range of applications in both natural and artificial materials, such as water collection, water electrolysis, droplet energy collection, medical diagnosis, etc. However, droplets and bubbles exhibit opposite wettability, and the inherent opposition between hydrophilicity and hydrophobicity presents a significant challenge in developing a manipulation system capable of manipulating both droplets and bubbles. Here, inspired by multiple natural organisms, a magnetic-actuated Janus spherical robot with switchable wettability as the driving core of droplets or bubbles, and a solid-like slippery surface as the manipulation platform is proposed, which achieves the dual programmable manipulation of droplets and bubbles. Furthermore, the Janus robot can achieve the transition from superhydrophobic to superhydrophilic within 8 min under UV light. It is noteworthy that the Janus robot demonstrates superior capabilities in the transport speed and carrier volume of liquid droplets (bubbles), which can reach 18 (13) cm s⁻¹ and 800 (500) µL, respectively. This strategy provides a novel and reliable method for the automated manipulation of droplets and bubbles and broadens their applications.