Strain Engineering of Wave-like Nanofibers for Dynamically Switchable Adhesive/Repulsive Surfaces

Engineering surfaces that enable the dynamic tuning of their wetting state is critical to many applications including integrated microfluidics systems, flexible electronics, and smart fabrics. Despite extensive progress, most of the switchable surfaces reported are based on ordered structures that suffer from poor scalability and high fabrication costs. Here, a robust and facile bottom-up approach is demonstrated that allows for the dynamical and reversible switching between lotus leaf (repulsive) and rose petal (adhesive) states by strain engineering of wave-like nanofiber layers. Interestingly, it is found that the controlled switching between these two distinctive states is sensitive to the shape of the nanofibers. Moreover, it is observed that the structural integrity of the nanofibers is fully preserved during multicycle dynamic switching. The application of these optimal structures is showcased as mechanical hands demonstrating the capture of water microdroplets and their subsequent release in a well-controlled manner. It is envisioned that this low-cost and highly scalable surface texture is a powerful platform for the design of portable microfluidics systems, and the fabrication of large-scale devices for ambient humidity harvesting and water purification.