Thermal Activation of Electrochemical Seed Surfaces for Selective and Tunable Hydrophobic Patterning.

Remarkable interfacial behaviors are observed in nature. Our efforts, directed toward replicating the structures, chemistries, and therefore functional properties of natural nonwetting surfaces, are competing with the result of billions of years of natural selection. The application of man-made surfaces is challenged by their poor longevity in aggressive environmental or applied service conditions. This study reports on a new approach for the creation of multiscale hierarchical surface patterns in metals, which exploits thermodynamic phenomena in advanced manufacturing processes. While hydrophobic coatings can be produced with relative ease by electrodeposition, these fractal-type structures tend to have poor structural integrity and hence are not durable. In this method, "seed surfaces" are directly written onto substrates by selective electrodeposition, after which they are irradiated by a large-area, pulsed electron beam to invoke a beading phenomenon, which is studied here. The length scale of these beads is shown to depend upon the melt time of the liquid metal. The created surfaces are shown to yield high water contact angles (145°) without subsequent chemical modification, and high adhesion properties reminiscent of the "rose petal" hydrophobic effect. The size and morphology and hence the hydrophobic effect of the surface beads generated are correlated with the thickness of the electrodeposited coating and hence the melt lifetime upon electron irradiation. This new rapid approach for tunable hydrophobic surface creation has applications for developing precision hydrophobic patterns and is insensitive to surface complexity.