Metastable Underwater Superhydrophobicity

Abstract

Superhydrophobicity is generally considered to be a thermodynamically stable wetting state. The stability of the plastron (the thin air film separating the substrate from the water in the superhydrophobic state) was studied in underwater experiments. The plastron exhibited a rapid decay after a well defined onset time, which was found to be dependent on the immersion depth. The plastron decay is explained in terms of a model, which is based on confocal microscopy measurements. The limited underwater plastron stability explains the rarity of permanently submerged superhydrophobic surfaces in nature and limits their scope for commercial applications.

Combining the lotus leaf effect with artificial photosynthesis: regeneration of underwater superhydrophobicity of hierarchical ZnO/Si surfaces by solar water splitting

“…30 According to previous studies, the gas diffusion rates are strongly affected by physical (hydrostatic pressure and micro/nanostructures of the surface) and chemical (surface energy) factors. 26,31 Although several investigations have been performed to understand the mechanism controlling the stability of the underwater non-wetting property, few studies have explored regenerating a stable gas interlayer to restore the underwater superhydrophobicity. 32 Up to now, superhydrophobic surfaces have only been shown to repair or reconstruct themselves via thermal or photochemical post-treatments under atmospheric conditions that restore their surface structures.…”

“…30 According to previous studies, the gas diffusion rates are strongly affected by physical (hydrostatic pressure and micro/nanostructures of the surface) and chemical (surface energy) factors. 26,31 …”

“…[16][17][18][19][20][21][22][23][24][25] Practical applications of non-wetting surfaces, however, have been impeded by the limited stability of their underwater superhydrophobicity. [26][27][28] According to the Cassie-Baxter model, the presence of an air interlayer on the submerged surface causes the non-wetting behavior, and thus, the stability of underwater superhydrophobicity is determined by the lifetime of the air (or gas) interlayer captured by the superhydrophobic surface. 29 However, the gas interlayer is unstable due to diffusion of the gas into the water.…”

Robust Cassie State of Wetting in Transparent Superhydrophobic Coatings

“…In the Wenzel state, the surface is completely wetted and the droplet pins to the surface, whereas in the Cassie state, the droplet wets the surface partially and air pockets form between the surface and water droplet. 1−3 The Cassie state of wetting provides a large apparent water contact angle with low contact-angle hysteresis and results in a roll-off superhydrophobic surface, which is desired for practical applications such as self-cleaning windows and solar panels, 4−6 underwater drag reduction, 7,8 and anticorrosion coatings. 9 Various successful methods have been developed by mimicking well-known examples from nature (e.g., Lotus leaves and butterfly wings) to prepare artificial superhydrophobic surfaces with the Cassie state of wetting using lithographic methods, 10−12 sol−gel techniques, 4,9,13−15 phase separation in polymer blends, 16 electrospinning, 17,18 and others.…”

Advances in Bio-inspired Tribology for Engineering Applications

“…As discussed in the earlier section where lotus leaf presents similar implications with its microtextured surface being mimicked efficiently to act as a non-wetting structure [99][100][101]. Even with over a decade's worth of research into this, there are still major problems like high contact angle hysteresis with limited olephobicity [101], failure under pressure, and inability to self-heal when physically damaged accompanied by high fabrication costs, restricting their practical applications [102][103][104]. To overcome these hurdles, researchers have looked for new bio-inspired surface.…”