Real-time control of uni-directional liquid spreading on a half-cone nanoshell array

Half-cone nanoshell arrays, fabricated by a simple and efficient colloidal lithography method, enable uni-directional liquid spreading on their hydrophilic asymmetric nanostructured surface. The preferred direction of the liquid flow is reversed when the surface is made hydrophobic. Accordingly, poly(N-isopropyl-acrylamide) is polymerized onto the surface for in-site controlling the transition of liquid spreading direction via its temperature dependent hydrophobicity. Furthermore, we also explain theoretically, that the spreading direction on hexagonal nanocone arrays is independent of the lattice orientation and only depends on the slanting direction. The insights gained from this work offer new opportunities for smart microfluidics, water harvesting and making use of other wetting conditions on demand.