Energy Dissipation due to Capillary Interactions: Hydrophobicity Maps in Force Microscopy

The energy dissipation process involved in the formation and rupture of a nanometer-sized capillary-condensed water bridge is theoretically analyzed. With the help of numerical simulations, the dissipation contrast in amplitude-modulated atomic force microscopy is shown to be a result of a nontrivial interplay between the energy dissipated in each rupture process and the bistable motion of the cantilever. In the repulsive high amplitude regime, the dissipated power is a function of the tip and sample contact angles being independent of the elastic properties of the system. Working in this regime, energy dissipation images in air can be regarded as surface hydrophobicity maps.