Dropwise condensation is a phenomenon of common occurrence in everyday life, the understanding and controlling of which is of great interest to applications ranging from technology to nature. Scalable superhydrophobic textures on metals are of direct relevance in improving phase change heat transport in realistic industrial applications. Here we reveal important facets of individual droplet growth rate and droplet departure during dropwise condensation on randomly structured hierarchical superhydrophobic aluminum textures, that is, surfaces with a microstructure consisting of irregular re-entrant microcavities and an overlaying nanostructure. We demonstrate that precoalescence droplet growth on such a surface can span a broad range of rates even when the condensation conditions are held constant. The fastest growth rates are observed to be more than 4 times faster as compared to the slowest growing droplets. We show that this variation in droplet growth on the hierarchical texture is primarily controlled by droplet growth dynamics on the nanostructure overlaying the microstructure and is caused by condensation-induced localized wetting nonuniformity on the nanostructure. We also show that the droplets nucleating and growing within the microcavities are able to spontaneously navigate the irregular microcavity geometry, climb the microtexture, and finally depart from the surface by coalescence-induced jumping. This self-navigation is realized by a synergistic combination of self-orienting Laplace pressure gradients induced within the droplet as it dislodges itself and moves through the texture, as well as multidroplet coalescence.

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...