Underwater Acoustic Camouflage by Wettability Transition on Laser Textured Superhydrophobic Metasurfaces

• Published in: Advanced materials interfaces Vol. 11; no. 24
• Main Authors: Mezzapesa, Francesco P., Gaudiuso, Caterina, Volpe, Annalisa, Ancona, Antonio, Mauro, Salvatore, Buogo, Silvano
• Format: Journal Article
• Language: English
• Published: Weinheim John Wiley & Sons, Inc 01.08.2024; Wiley-VCH
• Subjects: Acoustic attenuation; Acoustic waves; Acoustics; Broadband; Hydrophobic surfaces; Hydrophobicity; Laser beam texturing; Lasers; Liquid-solid interfaces; Metastable state; Sound fields; Spectral sensitivity; Submerging; superhydrophobicity; surface functionalization; Time dependence; ultrafast laser texturing; Ultrasonic imaging; Underwater acoustics; Wave attenuation; Wettability; wettability transition
• ISSN: 2196-7350; 2196-7350
• DOI: 10.1002/admi.202400124

The superhydrophobicity of submerged surfaces typically pertains to the trapped air film at the liquid–solid interface, subject to wettability transitions from a Cassie–Baxter state to more unstable states that gradually collapse to high retention regimes, which are energetically more favorable. In this work, the dynamic evolution of those transient metastable states is correlated to the underwater acoustic performance of laser textured superhydrophobic surfaces, resolving the dependence of the ultrasound spectral response with the immersion time to capture the genuine contribution of the hierarchical subwavelength morphology, regardless of the air layer effects. Acoustic wave attenuation of the incident ultrasound energy is extensively quantified in transmission, accounting for instantaneous broadband sound blocking (>30 dB) within the spectral range 0.5–1.5 MHz. As a result of the air layer detachment with the immersion time, transmission coefficients increase accordingly, while acoustic fields in reflection unexpectedly evolve toward stealthiness and naïve acoustic camouflage, mostly ascribable to dissipative mechanisms at air layer interfaces. The intrinsic decay of the air layer effect is tentatively determined at different frequencies, since quantitative understanding of the transient lifetime governing underwater surface wettability is critical to design stable superhydrophobic character of laser induced subwavelength metastructures on the most promising acoustic materials – from eco‐friendly natural to artificial. Unconventional functionalities of laser induced multi‐scale hierarchical metasurfaces are demonstrated to gain control over the acoustic response of submersed lightweight materials. Specifically, fs‐laser textured metastructures on the surface of aluminum foils are investigated to artificially induce superhydrophobicity and infer how any wettability transition (i.e. time‐varying wetting states) may affect their ultrasound performance in water.