Size dependent motion of nanodroplets on chemical steps

Nanodroplets on chemically structured substrates move under the action of disjoining pressure induced forces. A detailed analysis of them shows that, even in the absence of long-ranged lateral variations of the effective interface potential, already the fact that due to their small size nanodroplets do not sample the disjoining pressure at all distances from the substrate can lead to droplet motion toward the less wettable part of the substrate, i.e., in the direction opposite to the one expected on the basis of macroscopic wettability considerations.