Second-Level Microgroove Convexity is Critical for Air Plastron Restoration on Immersed Hierarchical Superhydrophobic Surfaces

Abstract

Air plastrons trapped on the surfaces of underwater superhydrophobic surfaces are critical for their function. Fibrillar morphologies offer a natural pathway, yet they are limited to a narrow range of liquid-surface systems and are vulnerable to pressure fluctuations that irreversibly destroy the air layer plastron. Inspired by the convexly grooved bases of water fern (Salvinia) leaves that support their fibrous outgrowths, we focus on the effect of such second-level grooved structures or microgrooves on the plastron restoration on immersed threedimensional (3D)-printed hierarchical surfaces. Elliptical, interconnected microgrooves are fabricated with varying surface curvatures to study the effect of their morphology. Immersion experiments reveal that the convex groove curvature stabilizes a seed gas layer (SGL) that facilitates plastron restoration for all immersed hydrophobic surfaces. Theoretical calculations and atomic-scale computations reveal that the SGL storage capacity that sets the SGL robustness follows from the liquid menisci adaption to the groove geometry and pressure, from micro-to nanoscales, and it can be further tuned using separated grooves. Our study highlights groove convexity as a key morphological feature for the design of second-level architectures for underwater air plastron restoration on hierarchical superhydrophobic surfaces.

Recent Advances in Superhydrophobic Materials Development for Maritime Applications

“…[92] Inspired by the convexly grooved bases of Salvinia leaves supporting eggbeater-shaped fibrillar outgrowths, Han et al conducted a comprehensive investigation into the impact of various parameters, such as groove surface curvatures and groove spacings and depths, on the seed gas layer robustness and restoration of their air plastron at the second level grooves. [93] The designs were realized using 3D projection micro-lithograph stereo exposure system (PμSL) and photosensitive resin as the printing material (Figure 5c). Through a combination of experimental testing, nanoscale computations, and theoretical analysis, the study revealed the crucial role of groove convexity in designing second level microstructures for stable gas layer and effective underwater air plastron restoration.…”

“…Reproduced with permission. [ 93 ] Copyright 2022, American Chemical Society. d) a fused filament fabrication (FFF)‐type 3D printing for creating magnetically controllable micro‐patterned wall arrays for droplet control.…”

“…c) a projection microstereolithography (PμSL) for fabricating cylindrical pillar shapes with convex groove curvature that facilitated plastron regeneration. Reproduced with permission [93]. Copyright 2022, American Chemical Society.…”

Recent progress in bio-inspired macrostructure array materials with special wettability—from surface engineering to functional applications

“…Apart from the above-mentioned applications, bio-inspired MAAMs-SW have demonstrated important applications in air retention under water [96,277,278], smart wettability [279][280][281][282], mechanical stability [98,283,284], and in other fields. Inspired by the long-term underwater air layer retention ability of S. molesta, Zhang et al [96] developed a 'top-constrained self-branching' method to fabricate a superhydrophobic four-branch macrostructure, which was embedded with hydrophilic microspheres (figures 28(a)-(c)).…”

The fabrication of robust and highly efficient oil–water separation filters via the high temperature sintering of silica micropower

“…Many studies have presented hierarchical or re-entrant structures to increase overall lifetime by prolonging the transition. 2,[11][12][13][14][15] Though materials design can slow the transition to a wetted state, the implementation of mechanisms to maintain or reintroduce air to the system ensures the longest plastron lifetime and thus the longest lifetime of properties. One way of achieving this is by using porous superhydrophobic materials and pneumatic air control.…”