Green and Flexible Superhydrophobic Surfaces for Friction and Drag Reduction Using "Pattern Elongated" Nanoimprinting

Superhydrophobic surfaces have attracted a lot of interest due to their usability in various fields such as antibacterial and self-cleaning surfaces, heat transfer applications, and hydrodynamic drag reduction. Despite their potential, fabricating such surfaces typically requires complex processes and costly equipment. Here, we introduce an ultrafast, simple, and environmentally friendly method for fabricating nanostructured superhydrophobic surfaces via thermal nanoimprinting using randomly nanostructured aluminum surfaces as masters. Reusable Al masters bearing ∼250 nm boehmite nanostructures are produced by immersing aluminum in boiling water. Then, a modified thermal imprinting step, termed "pattern elongated" nanoimprinting, is used to pattern flexible and inherently hydrophobic polyethylene foils. Thus, the replicated pattern is elongated during demolding, yielding highly dense, filamentary structures. As a result, superhydrophobic polyethylene foils, exhibiting high contact angles, low hysteresis, and reduced interfacial friction, as indicated by friction measurements, are fabricated. Furthermore, computational fluid dynamics simulations are performed for three cases in which such surfaces can be used (i.e., in a microchannel, in a rectangular channel, and over an open surface), showcasing significant reductions in pressure drop compared with untreated surfaces, highlighting their high potential for drag reduction in pressure-driven microfluidics and low-friction maritime applications.