Overdamped dynamics of liquid drop contact lines

The dynamics of how drops move across solid surfaces are not well understood. We measure the macroscopic shape — contact angle and drop width — of drops of pure solute as they are aspirated from carefully prepared surfaces. The dynamics depend on both the speed at which the drops are removed and on the length of time that they sit on the surface before aspiration. Inspired by solid-solid friction, we simulate contact line motion with overdamped dynamics and show that fitting for just two parameters, the damping coefficient and the equilibrium contact angle, allows us to capture the behavior observed in experiments. We explore the physical picture suggested by the parameters of the simulations.