Nanoengineered surfaces have received significant interest for the manipulation of liquids in microfluidic systems. In this work, we present three-dimensional nanostructures that can control liquid film thickness and the directionality of the liquid spreading. We fabricated silicon nanopillars ranging from 200 nm to 800 nm in diameter and heights of approximately 5 μm. In the presence of notches on the pillars, the liquid separates into multiple layers of liquid films. The thicknesses of the liquid layers subsequently increase as the film propagates, which is determined by the specific position and geometry of the notches. In the presence of asymmetric nanopillars, where the pillars have deflection angles ranging from 0–50 degrees, directional spreading of water droplets can be achieved. The liquid spreads only in the direction of the pillar deflection and becomes pinned on the opposite interface. We performed detailed measurements and developed models to predict the behavior based on pillar geometries. The insights gained from this work offer promise for enhanced control of liquids in microfluidic systems.

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