Contact line hysteresis and elastic depinning

We revisit the classic problem of contact line hysteresis with a new technique where we use the force transmitted to a flexible sheet being draped onto or peeled away from a liquid surface to precisely measure contact line dynamics over both short and long timescales. When driven in either the advancing or retreating direction, the contact line is first pinned to the sheet, and then beyond a threshold depins and slips with a small, but finite velocity. When the driving is halted, the contact line first relaxes rapidly with a speed that depends on the driving velocity, and then decays more slowly towards equilibrium. We compare our experimental results to the theory of elastic depinning transitions, which makes quantitative predictions for the many stages of interface dynamics.