Evaporation of droplets on strongly and weakly pinning surfaces and dynamics of the triple line

Evaporation of water droplets deposited on metal and polymer substrates was studied. The evaporated droplet demonstrates different behavior on weakly pinning (polymer) and strongly pinning (metallic) surfaces. When deposited on polymer surfaces, the evaporated droplet is featured by stick-slip sliding, whereas on strong-pinning metallic surfaces it does not show such kind of motion and demonstrates the giant contact-angle hysteresis. Stick-slip motion of droplets is described satisfactorily by the Shanahan-Sefiane model relating this kind of motion to surmounting potential barriers caused by the pinning of the triple (three-phase) line. The experimentally established "stick" times coincide with the values predicted by the Shanahan-Sefiane theory. The values of potential barriers are reported. The notion of the equilibrium contact angle is refined.