(296f) Measuring Contact-Line Mobility Using Drop Resonance

Contact-line mobility characterizes how fast a liquid can coat a solid support. During rapid movement of liquid across a solid, the contact angle changes dynamically in response to changes in contact line speed. Mobility captures this far-from-equilibrium behavior. For sufficiently rapid movement of thin liquids in contact with low-hysteresis supports, motions are largely inviscid. In this regime, surface tension and liquid inertia compete to influence the interface shape near the three-phase contact line. We use a mechanical oscillator to induce resonance in a supported liquid drop and resolve contact line motions using high-speed imaging. The mobility parameter is then extracted from measurements of contact line displacement, contact line speed and contact angle. The introduced procedure enables the resonant-drop dynamical goniometer (RDG) and recovers the traditional contact-angle versus contact-line speed diagram as a limiting case. Advantages of the RDG are summarized.