Superhydrophobicity vs. Ice Adhesion: The Quandary of Robust Icephobic Surface Design

Abstract

to spectacular rebound events of droplets upon impact [ 1,2 ] and ultra-low adhesion to water. [3][4][5][6][7][8][9] Unfortunately, depending on surface texture, superhydrophobic (nonwetting) properties can be lost either by water condensation in the texture [ 10 ] or drop impact beyond a texture-specifi c velocity (critical velocity), when rebound to sticky transition occurs. [ 11 ] In both cases, the micro-/nanocavities of the surface texture are fi lled with water transitioning the droplet from a non-wetted state, Cassie-Baxter, [ 12 ] to a wetted state, Wenzel [ 13 ] state. In this context, the challenge is to design robust superhydrophobic surfaces, which maintain water repellency at very high impact speeds, and that for application-relevant materials. A recent study [ 14 ] shows that both the surface texture and the contact angle play an important role in the droplet impact event. Moreover, experimental studies on multitier surface textures with nanoscale morphology reveal indeed the potential of such surfaces to resist rebound to sticky transition also at high impact speeds. [15][16][17][18] Recently, Checco et al. [ 17 ] presented a novel block copolymer based surface with well-defi ned nanotexture (feature size of ≈10 nm) resisting impalement up to 10 m s −1 with millimeter-sized water droplets. In another approach, carbon composite (carbon nanotube or graphene) and hydrophobic polymer-based superhydrophobic surfaces also exhibited high droplet meniscus impalement resistance up to impact speeds of 5 m s −1 . [ 15,17 ] However, the materials in these works were not application relevant metals and the relationship between ice adhesion and water repellency was not explored.Here, we target aluminium as a platform, an important material representing metals with respect to imparting superhydrophobic and icephobic properties, due to its frequent presence in a broad palette of engineering applications. [ 16 ] With the help of anodization, it is possible to generate and control surface texture and, in combination with surface chemistry, surface wettability. [19][20][21][22][23][24][25] Recently, Lai et al. [ 26 ] and Hu et al. [ 27 ] exploited anodization to fabricate nanotube-based superhydrophobic surfaces with extremely low water adhesion. With the same line of thought, employing anodization and followed by an acid etching process, we fabricated three surface types with nanotexture morphologies: Two consisting solely of a closely The mesoscale, multitier texture of the lotus leaf has served as an inspiration to fabricate surface designs with controllable superhydrophobic properties, targeting a broad range of applications. The choice of material for such designs is directly related to surface performance, in particular under adverse and realistic conditions. Due to its importance in many applications, here aluminium is employed as a material platform and identify key porous hierarchical textures, yielding extraordinary impalement-resistant behavior: Droplet repellency is demonstrated consistently for water imp...

Nanotextured Surfaces for Anti-Icing

“…The nf surface also showed a high impalement resistance, resisting jets with speeds of 11 m/s (~ 840), which is consistent with the previous study on the similar nanofiber structures [23]. Note that, the previous study [23] showed that similar nanofiber structures on a smooth aluminum surface can repel impact of 2-mm sized water drops up to ~3000. However, the surfaces were not tested with jet impact, which offers a more severe test of durability.…”

Mechanically Robust Transparent Anti‐Icing Coatings: Roles of Dispersion Status of Titanate Nanotubes

“…Anti-icing coatings are highly valued for preventing or alleviating adverse consequences of ice accretion on airplanes, marine structures, satellites, weapon systems, and energy-harvesting devices. In the past two decades, tremendous efforts have been devoted to the study of anti-icing performance of superhydrophobic coatings inspired by the lotus effect [1] and coatings are mechanically weak. An earlier study of transparent anti-icing coating was conducted by Kimura et al, [8] and one of their reported coatings was water-repellent and transparent.…”

Design, characterisation and performance evaluation of a Peltier-driven cryo-adhesive fixture for manufacturing operations

“…A more likely cause for the behaviour in Figure 14 is the current experimental setup which means that the load/force is not applied at the surface, but at a distance from the surface. As detailed by Maitra et al [38], this results in the simultaneous action of tensile and shear stresses, which can yield different results to those obtained when applying shear forces alone.…”

“…The fixture was carefully located to let the freelyhanging chain rest directly above the M6 hole in the specimens where the force would be applied. To apply ideal shear, the point of application of the force should be as close as possible to the workpiece/ice plate contact line [38], to avoid the introduction of tensile forces. Due to the nature of the experimental setup where the connection between the Instron and the workpiece was made using the chain, and the fact that the workpiece specimens were place at the centre of surface of much greater area, applying the shear force immediately at the ice plate surface was not possible.…”