Fig. 2.

Droplets move on flat surfaces with stiffness gradients. (A) Schematic diagram of flat chemically homogeneous substrates with gradients of stiffness. A flat layer of soft, silicone gel is deposited on a hard, lenticular array creating gradients in the thickness (or stiffness) of the gel. (B and C) Photographs of glycerol droplets after deposition with an atomizer. The dark horizontal bands are located at the thickest regions of the substrate. The spacing between the bands is 170 μm. B and C were taken 5 min and 5 h after application, respectively. (D) Probability density of final droplet locations from 13,300 droplets as a function of substrate thickness and drop radius. The dashed curve is the theoretical prediction for final position of moving droplets. (E) Size distribution of observed droplets.