Directional Mobility and Adhesion of Water Drops on Patterned Superhydrophobic Surfaces

Directional mobility and controlled adhesion of water drops were obtained on superhydrophobic paper surfaces by generating high surface energy ink patterns using commercial desktop printing. By changing the curvature/shapes of the ink patterns, geometrical constraints were imposed on the movement of the three-phase liquid/solid/vapor contact line. With proper design of pattern shapes, the critical sliding angle of water drops was manipulated with respect to different directions. Adhesion tunability of water drops on superhydrophobic paper was established by design of chemical heterogeneity. Printing of 'checker' ink patterns with appropriate area fraction and feature dimensions allowed variation in the critical sliding angle of water drops. The manipulation of directional mobility and adhesion of water drops on superhydrophobic paper surfaces allows the design of novel components such as 2D flow paths, gates/diodes, junctions and drop size filters for emerging 2D paper-based microfluidics technology for biomedical diagnostic applications. (C) Koninklijke Brill NV, Leiden, 2011