Simultaneous Detection and Repair of Wetting Defects in Superhydrophobic Coatings via Cassie–Wenzel Transitions of Liquid Marbles

Abstract

Superhydrophobic materials that prevent unwanted liquid adhesion can easily lose this property because of limited mechanical durability despite topological/chemical control and/or robust material selection. Here, long-lasting superhydrophobic coatings with a system to effectively detect and repair damaged areas with "liquid marble," a droplet covered with hydrophobic nanoparticles, are reported. The particles prevent direct contact between the droplet and the substrate (Cassie state). However, they can adhere to the nonsuperhydrophobic damaged area in response to the substrate wettability via an external force or an increase in liquid volume via penetration of the outer nanoparticle layer (Wenzel state). This Cassie-Wenzel transition thus induces self-assembly of the nanoparticles onto the non-superhydrophobic area in response to the wettability, restoring superhydrophobicity.

Liquid Marble Patchwork on Super‐Repellent Surface

“…However, the interparticle distance increases with decreasing packing density, and the inner liquid starts to interact with the outer environment at the critical value. [10,34] Whether the inner liquid interacts or not is determined by the maximum interparticle distance D max exceeding a critical value D c : [34] θ θ θ ( ) ( )…”

“…[34] However, on the hydrophilic surface, the state switch is not reversible as the transition from the capillary to the funicular state is irreversible (Figure 2B). [10] These different scenarios depend on which state is stable when the particle is adhered to or wetting the surface. This is quantified by comparing the adhesion energy between the inner droplet and the surface (ΔE wet ) [34] with ΔE adh .…”

“…LMs behave as non-wetting soft solids and roll-off solid/liquid surfaces without undesirable adhesion losses. This concept is attracting enormous attention owing to the potential applications of these types of materials, such as droplet fluidics, [7,8] sensor platforms, [9] healing agents, [10,11] biosystems, [12][13][14] and chemical reactors. [15,16] Based on these demands, efforts have been made to design functional LMs using various stimuli-responsive hydrophobic particles, [17] including those responsive to UV-vis light, [18,19] magnetic fields, [20][21][22] temperature, [23] ultrasound, [24] and pressure.…”

Facile optimization of hierarchical topography and chemistry on magnetically active graphene oxide nanosheets

“…which are otherwise impossible to achieve with the same liquid wettability embedded on macro-scale objects. [22][23][24][25][26][27][28][29][30][31][32] In the past, superhydrophobicity was achieved on microparticles by associating a low surface energy coating through weak chemical bonding/interactions-including metal-thiol bonding, hydrogen bonding, ionic interactions, etc. These weak interactions and bondings are less likely to be sustained in practically relevant, diverse and harsh scenarios (i.e., extremes of pH, salinity, etc.).…”

Self‐Supplying Liquidity Oil‐Adsorbed Slippery Smooth Surface for Both Liquid and Solid Repellency

“…as optical scattering, low mechanical durability (easily worn), limited wettability, poor tolerance against extremely conditions, and limited self-healing ability, due to the rough surface as the typical bottleneck. [18,19] In response to the above demands, liquid-infused surfaces (LISs) inspired by the pitcher plant (Nepenthes) have been developed. [20,21] The first LIS was reported by Wong et al, who developed a slippery liquid-infused porous surface (SLIPS) that forms a stable lubricant interface between the solid and the target liquid by locking a hydrophobic liquid layer (LL) into a porous base layer (BL).…”