Aerophilic surfaces immersed underwater trap films of air known as plastrons. Plastrons have typically been considered impractical for underwater engineering applications due to their metastable performance. Here, we describe aerophilic titanium alloy (Ti) surfaces with extended plastron lifetimes that are conserved for months underwater. Long-term stability is achieved by the formation of highly rough hierarchically structured surfaces via electrochemical anodization combined with a low-surface-energy coating produced by a fluorinated surfactant. Aerophilic Ti surfaces drastically reduce blood adhesion and, when submerged in water, prevent adhesion of bacteria and marine organisms such as barnacles and mussels. Overall, we demonstrate a general strategy to achieve the long-term stability of plastrons on aerophilic surfaces for previously unattainable underwater applications.
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We thank A. Marmur for fruitful discussions on the plastron stability of Ti-APhS. A.B.T. thanks N. Vogel and J. Harrer for help with AFM measurements and E. Alkhateeb for help with X-ray diffraction measurements. A.B.T. thanks F. Krause from Keyence Deutschland GmbH for providing a laser confocal microscope for surface roughness measurements. W.H.G. and A.B.T. are indebted to L. Nicholson (Master of Arts) for proofreading the manuscript. We acknowledge the provision of facilities and technical support by Aalto University at OtaNano’s Nanomicroscopy Center (Aalto-NMC). A.B.T., P.S., W.H.G. and B.F. thank the Deutsche Forschungsgemeinschaft (DFG; SCHM 1597/38-1 and FA 336/13-1) for their financial support. A.B.T. acknowledges the Emerging Talents Initiative (ETI) of the Friedrich-Alexander-Universität Erlangen-Nürnberg (grant agreement number 5500102). This work was funded in part by grants from the German Science Foundation (DFG; FA 336-12/1, TRR-SFB 225 Projects A01 and C02). J.V.I.T. acknowledges funding from the Academy of Finland Center of Excellence Program (2022–2029) in Life-Inspired Hybrid Materials (LIBER), project number 346112. M. Backholm acknowledges postdoctoral funding from the Academy of Finland (grant agreement number 309237). M. Bruns, B.K., H.A.N., M.L., Z.M.C., J.V.I.T. and R.H.A.R. acknowledge funding from the Academy of Finland Center of Excellence Program (2022–2029) in Life-Inspired Hybrid Materials (LIBER, project number 346109). S.S. acknowledges funding from the Office of Naval Research, US Department of Defense (grant N00014-17-1-2153). S.K. and J.A. acknowledge funding from the Office of Naval Research, US Department of Defense (grants N00014-15-1-2323 and N00014-17-1-2913) and the Department of Energy (award DE-SC0005247).
The authors declare no competing interests.
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Supplementary Figs. 1–16, Tables 1 and 2 and Materials and Methods.
Spreading of water drops on the as-anodized (super-hydrophilic) Ti surface.
Adhesion of water droplets to Ti-APhS. The substrate tilt angle is ~0 degrees.
Measurements of the adhesive force on Ti-APhS using MFS.
Dynamic characteristics of air bubbles on Ti-APhS after 78 days of continuous immersion underwater.
Wetting properties of Ti-APhS before and after 14 and 67 days underwater at 0.5 m depth. The substrate tilt angle is 10 degrees.
Hot-water and cold-water jet impinging Ti-APhS. Jet pressure, 70 psi. An equivalent impinging mass is 900 grams.
Plastron stability under bending and twisting of Ti-APhS underwater.
WCA hysteresis before and after sand abrasion by 0.8 mm yttria-stabilized zirconia beads.
Affinity and CA hysteresis of blood to Ti-APhS.
Blood droplet on Ti-APhS removed by paper wipe.
Blood affinity to bare Ti immersed for 1 s, and Ti-APhS immersed 99 times at 1 s each.
Bare Ti and Ti-APhS in 1.5 M NaOH aqueous electrolyte under an applied potential of 10 V.
Blood droplets roll off bare Ti and off Ti-APhS immersed 99 times in the container with blood.
Water affinity, WCA hysteresis and blood affinity to aluminium SHS.
Sliding time window analysis of the bare Ti sample, super-hydrophilic Ti sample and Ti-APhS exposed to E. coli.
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Tesler, A.B., Kolle, S., Prado, L.H. et al. Long-term stability of aerophilic metallic surfaces underwater. Nat. Mater. (2023). https://doi.org/10.1038/s41563-023-01670-6