is the liquid-solid interfacial energy. For a millimetric-sized EGaIn droplet and by other groups. Far from the surface, the droplet experiences no force F = 0, but when the droplet contacts the C4 surface in air (Fig. ), we observe a sudden capillary snap-in force F snap = 1.6 ± 0.1 µN due to the surface tension of EGaIn. Since the surface tension of the EGaIn droplet is much larger than that of water, the formation of water capillary bridges due to water capillary condensation is not an important contributing factor to F snap (see also discussion on the effect of humidity in Supporting Figure ). Because the droplet makes a finite contact angle θ < 180 • on the surface, there is strong adhesion to the surface and a critical adhesion force F adh = 2.2 ± 0.1 µN is required to remove the droplet. We also observed a large hysteresis between the approach and retract curves, represented by the dashed and full lines, respectively, in Figures . We can quantify the amount of hysteresis by integrating the area between the approach and retract curves (shaded gray in Figure ).