Scalable fabrication of microtextured hydrophobic surfaces via two-step wet etching of aluminum templates for air-layer-induced friction and drag reduction

초록

Microtextured hydrophobic surfaces can significantly reduce interfacial friction and hydrodynamic drag by trapping stable air pockets (Cassie-Baxter state) between surface features and the liquid. In this study, we present a low-cost and scalable method to fabricate microtextured polydimethylsiloxane (PDMS) surfaces via replication of aluminum molds produced by a simple two-step wet etching process, consisting of anisotropic etching followed by isotropic etching. The resulting PDMS surfaces exhibited irregular microstructures with surface roughness ranging from 4.3 to 5.1 & micro;m, high apparent contact angles up to 136.7 degrees, and air-pocket coverage of up to 30.5%, enabling stable interfacial slip. Friction and drag characteristics were systematically evaluated using a custom dual-beam leaf flexure system and a rotating propeller setup. Compared with smooth PDMS, the microtextured surfaces achieved up to 70% reduction in friction at the solid-solid interface, 32% reduction at the solid-liquid interface, and 20% reduction in underwater drag. The drag-reduction performance remained stable over 120 h of continuous operation. These results demonstrate that microtextured surfaces reduce hydrodynamic resistance through air-layer-induced slip and delayed flow separation, providing a practical strategy for scalable drag-reducing surfaces.

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