One-Step Fabrication of Flexible Bioinspired Superomniphobic Surfaces

Fabrication of Flexible and Re-entrant Liquid-Superrepellent Surface Using Proximity and PNIPAM-Assisted Soft Lithography

The nature-inspired flexible and re-entrant liquid-superrepellent surface has attracted significant attention due to its excellent superomniphobic performance against low-surface-tension liquids. Although conventional photolithography and molding methods offer the advantage of large-area manufacturing, they often involve multiple double-sided alignment and exposure steps, resulting in complex procedures with long processing cycles. In this study, we proposed a straightforward single-exposure ultraviolet proximity lithography method for re-entrant liquid-superrepellent surface fabrication using a photomask with a coaxial circular aperture and ring. A theoretical calculation model for the three-dimensional light intensity distribution in proximity lithography was developed for the prediction of feature sizes for both singly and doubly re-entrant microstructures. Soft lithography techniques, which rely on surface modification and the modulation of the transfer material's flexibility, efficiently optimized the fabrication of flexible re-entrant molds and patterns. By incorporating nanoclay-modified poly(N-isopropylacrylamide) (PNIPAM) into the molding process, we fabricated a three-layer hierarchical structure featuring micrometer-scale wrinkles, re-entrant microstructures, and nanoscale fluorinated silica particles, significantly enhancing the surface's robustness and pressure resistance. The resulting large-area flexible and re-entrant liquid-superrepellent surface demonstrated excellent superomniphobic self-cleaning performance and satisfactory optical transparency, as evidenced by reflection and transmission experiments, showcasing its potential applications in self-cleaning, membrane distillation, and digital microfluidics.

Design of highly robust super-liquid-repellent surfaces that can resist high-velocity impact of low-surface-tension liquids

Super-liquid-repellent surfaces capable of preventing wetting with various liquids have tremendous application. However, high liquid repellency relies on surface texturing to minimize the solid-liquid interfacial contact, which generally results in impaired interface robustness and pressure resistance. Consequently, the surface tends to undergo a Cassie-Baxter to Wenzel wetting transition and loses liquid repellency under high-velocity liquid impact, especially for low-surface-tension liquids. Here, surface design through combining the nanoscale effect and doubly reentrant structure is demonstrated to solve the above challenge. By utilizing a facile colloidal lithography process, robust liquid repellent surfaces featuring nanoscale doubly reentrant (NDR) structures are constructed. The nanoscale features ensure sufficient triple contact line density at a low solid-liquid contact fraction to enhance the capillary force for liquid suspension. In conjunction with the doubly reentrant topography that maximizes the upward component of capillary force, such NDR surfaces enable an extremely robust solid-liquid-gas composite interface. As a result, the prepared NDR surface maintain excellent repellency upon high-velocity impact of various liquids, including ethylene glycol drops with a Weber number (We) above 306 and ethanol drops with a We of 57. The above findings can help the development of super-liquid-repellent surfaces applicable to harsh conditions of high-velocity liquid impact or high hydrostatic pressure.

Enhanced Anti-Wetting Methods of Hydrophobic Membrane for Membrane Distillation

Increasing issues of hydrophobic membrane wetting occur in the membrane distillation (MD) process, stimulating the research on enhanced anti-wetting methods for membrane materials. In recent years, surface structural construction (i.e., constructing reentrant-like structures), surface chemical modification (i.e., coating organofluorides), and their combination have significantly improved the anti-wetting properties of the hydrophobic membranes. Besides, these methods change the MD performance (i.e., increased/decreased vapor flux and increased salt rejection). This review first introduces the characterization parameters of wettability and the fundamental principles of membrane surface wetting. Then it summarizes the enhanced anti-wetting methods, the related principles, and most importantly, the anti-wetting properties of the resultant membranes. Next, the MD performance of hydrophobic membranes prepared by different enhanced anti-wetting methods is discussed in desalinating different feeds. Finally, facile and reproducible strategies are aspired for the robust MD membrane in the future.