Spatial Control of Condensate Droplets on Superhydrophobic Surfaces

Super-bi-philic surfaces have been fabricated and characterized using environmental scanning electron microscopy (ESEM) to demonstrate spatial control of microscale droplets during condensation. The surfaces are composed of biotemplated nickel nanostructures based on the self assembly and metalization of the Tobacco mosaic virus. They are then functionalized using vapor-phase deposition of trichlorosilane, and lithographically patterned to create engineered nucleation sites. The resulting surfaces are primarily superhydrophobic (θ ≈ 170°) with arrays of superhydrophilic islands (θ ≈ 0°) with diameters of 3 μm and center-to-center pitches varying from 10 – 50 μm. During condensation the superhydrophilic islands promote nucleation resulting in spatial control of the condensate, which forms into ordered rectangular arrays (a,b). This spatial control has been shown to produce efficient jumping-mode condensation for pitches greater than 15 μm, as well as promote multi-droplet events (c). Additionally, super-bi-philic surfaces have been shown to delay the transition to a flooded state at high supersaturations, as compared to superhydrophobic designs.