Dissipation by oscillatory contact-lines*

Contact-line (CL) effects influence the extent of energy dissipation when a liquid moves across a solid support, as when a liquid undergoes rapid spreading. For sufficiently rapid spreading, inertia competes with capillarity to influence the interface shape near the support. A traditional approach to evaluate CL dissipation calculates the mechanical work associated with the deformed interface based on measurements local to the CL. These measurements are achievable with our set-up where we use resonant-mode plane-normal support oscillations to drive lateral contact-line motion of droplets in the inertial-capillary regime (Re high and Ca low). In contrast to the traditional approach, by tuning the driving frequency near resonance, we obtain the scaled peak height (amplification factor) and phase difference to yield a non-dimensional characterization of dissipation (damping ratio). This approach requires only the displacements of the drop peak and the driving platform as inputs, independent of measurements local to the CL. CL dissipation is isolated from other modes of dissipation and partitioning of dissipation between CL and bulk sources is discussed.