Figure 2
Explaining the wetting-transition using local force balance model. (a) Schematic showing the base of a suspending droplet (left), top view of the droplet base (middle), and unit-cell configuration (right). The micropillar in zone A1 (unit cell) experiences larger downward force (FLaplace) than the peripheral micropillars (see Supplementary Fig. S-2) and hence used for defining the wetting-transition criteria. (b) Schematic (side-view) of a droplet curvature between two adjacent micropillars showing the downward Laplace pressure force and upward capillary forces, shown together (left), shown separately (middle & right). The Laplace pressure force also acts on the top of the micropillar (not shown) but cannot affect the wetting-transition phenomenon. (c) Shows the determination of the critical force per unit length (FPL) value experimentally. The water droplet started sliding down (depinning) along sidewalls of the inner micropillars when the FPL reached a critical value of 0.090 ± 0.005 N/m. The scale bar in (c) is 200 μm.
