3D printed multiscale superhydrophobic structures with promoted bounce behavior, environmental stability, and ultralong freezing delay

Minimizing liquid-solid interfacial contact is often preferred for various natural and engineering systems in the long-term servicing period, ranging from the heat regulating of biological survival to anti-corrosion or anti-icing of aeronautical facilities. However, natural and biomimetic surfaces bounce off water drops with a constant contact time (classical inertial-capillary limit), and lose their superhydrophobicity with increased contact areas from room to harsh conditions (i.e., cold and humid). Reducing the solid-liquid interfacial contact time and sustaining contact areas of a single structure remain daunting challenges under broad temperature and humidity conditions. Here, a novel hierarchical structure with multiscale confined air pockets (CAPs), which exhibit some exceptional and unexpected properties of superior superhydrophobicity and environmental/mechanical/chemical stability, is proposed and realized via 3D printing and selective phase etching. The interaction process is shortened with a reduced contact time with the significantly positive pressure supported by the CAPs. Benefiting from sustained contact areas and stabilized superhydrophobicity, supercooling or freezing delay for an ultralong time (∼354 min) can be achieved in the subzero temperature and highly humid atmosphere. The hierarchical design method is scalable to the mass production, applicable to complex geometries and metallurgically bonded between in-situ phases and substrate, which exhibits superior repellency, broad environmental stability, and freezing delay abilities; thus, it is a promising strategy in areas as diverse as energy transfer, engineering, chemistry, biotechnology, and materials science.