4D printing of butterfly scale-inspired structures for wide-angle directional liquid transport

Abstract

Unidirectional liquid transport has been extensively explored for water/fog harvesting, electrochemical sensing, and desalination. However, current research mainly focuses on linear liquid transport (transport angle α = 0°), which exhibits hindered lateral liquid spreading and low unidirectional transport efficiency. Inspired by the wide-angle (0° < α < 180°) liquid transport on butterfly wings, this work successfully achieves linear (α = 0°), wide-angle, and even ultra-wide-angle (α = 180°) liquid transport by four-dimensional (4D) printing of butterfly scale-inspired re-entrant structures. These asymmetric re-entrant structures can achieve unidirectional liquid transport, and their layout can control the Laplace pressure in the forward (structure-tilting) and lateral directions to adjust the transport angle. Specifically, high transport efficiency and programmable forward/lateral transport paths are simultaneously achieved by the ultra-wide-angle transport, where liquid fills the lateral path before being transported forward. Moreover, the ultra-wide-angle transport is also validated in 3D space, which provides an innovative platform for advanced biochemical microreaction, large-area evaporation, and self-propelled oil-water separation.Agency for Science, Technology and Research (A*STAR)National Research Foundation (NRF)K.Z., X.L., and B.L. acknowledge the support of the National Research Foundation, Prime Minister's Office, Singapore under its Medium‐Sized Centre funding scheme through the Marine and Offshore Program. K.Z. and X.L. acknowledge the RIE2020 Industry Alignment Fund–Industry Collaboration Projects (IAF–ICP) Funding Initiative, as well as cash and in‐kind contribution from the industry partner, HP Inc., through the HP‐NTU Digital Manufacturing Corporate Lab. Z.G. acknowledge the support of the National Natural Science Foundation of China (52033002)