(color online) Droplets on substrates of different radii showing curvature selectivity through direct liquid flow. (a) The movement of a droplet of r_S = 15 between two spherical colloids (R = 10 and R = 30). The snapshots, from left to right, correspond to the time steps of 0, 400, 800, 1200, 1500, and 2000. (b) The movement of a droplet between a flat substrate and a spherical colloid with a radius of R = 30. The snapshots correspond to the time steps of 0, 500, 1000, 1500, 1800, and 2400. (c) The movement of a droplet between a flat substrate and a spherical cavity with a radius of R = 40. The snapshots correspond to the time steps of 0, 200, 900, 1500, 1700, and 2200. In the figure, the solid surfaces have a wettability of θ_Y = π/3.