Durable Super-repellent Surfaces: From Solid-Liquid Interaction to Applications

A super-repellent surface is a type of liquid-repellency material that allows for various liquid drops to bead up, roll off, or even bounce back. Known for its ability to remain dry, perform self-cleaning, and have a low adhesion, a super-repellent surface presents great advantages in a number of applications. These include antifogging, anti-icing, oil/water separation, and fluid drag reduction. To fend off the liquids or drops, super-repellent surfaces combine the merits of surface chemistry and physical structure. By taking advantage of a low surface energy to prevent liquid from spreading, the super-repellent surfaces utilize the micronano structure to provide a framework that confines the solid-liquid interactions. Compared to beading up the drop of water, the repellence of liquid with low surface tension requires the subtle design of surface structure to resist the wetting of liquids. However, the inherent instabilities of the fragile micronano structure of super-repellent surfaces and solid-liquid interactions further make the fabrication of super-repellent surfaces complex to withstand dynamic environments (friction or wear) during application. In addition, the transparency and thermal stability of super-repellent surfaces are also the restrictive factors in some special application scenarios. To solve these challenges, durable super-repellent surfaces that can repel various liquids, possess robust mechanical and thermal stability, and show high transparency have been explored extensively in recent years. In this Account, we systematically review our recent efforts to promote the super-repellent surfaces for real-world applications. Super-repellent surfaces that exhibit excellent resistance to various liquids, including liquids with low surface tension or high viscosity, were subtly designed and fabricated in some manner. Considering the stability of the wetting state at the solid-liquid interface, we established an evaluation system that includes highly curved surfaces and high Laplace-pressure conditions. To further perfect the wetting mechanism at the solid-liquid interactions, the dynamic wettability of super-repellent surfaces regulated by surface charge enrichment that was generated from solid-liquid interface separation was investigated. To resolve the bottleneck problem of the mechanical stability of super-repellent surfaces in real-world applications, a new decoupling material design mechanism was proposed, with a nanostructure that maintains water repellency and a microstructure providing durability. On the basis of the performance of the liquid-repellency, transparency, and mechanical and thermal stability of the super-repellent surfaces, a series of applications were demonstrated, such as microsphere synthesis, drop transportation and manipulation, and self-cleaning solar panels. Finally, a concise summary of this Account, including challenges and opportunities in super-repellent materials, has been provided. This research provides important guidance on solid-liquid interactions for the design of functional super-repellent surfaces and plays an important role in promoting large-scale industrial applications.