Droplets as force gauges on hydrophobic surfaces

Hydrophobic and superhydrophobic interactions can be characterized by measuring forces between drops and surfaces using force gauges that range from optical fibers to atomic force microscopy cantilevers. Here, we propose and implement an alternative methodology in which a nearly spherical drop itself serves as a force gauge. By obtaining dynamic contact angles, force constants of biological structures, and the force of adhesion on nonwettable surfaces, we demonstrate the robustness, wide applicability, and simplicity (neither profile fitting nor knowledge of the contact angle or area are required) of this technique.