Hysteresis alters the flow near a moving contact line: evidence from experiments and simulation

A moving contact line is a region where the interface between two immiscible fluids intersects a moving solid surface. The theoretical study by Huh & Scriven [1] reported a stress singularity near a moving contact line. The stress singularity is primarily caused by the application of the no-slip boundary condition on the moving plate, which is directly in conflict with a moving contact line. Several models have been proposed to resolve this singularity. A popular choice is to relax the no-slip condition and allow a finite amount of slip in the vicinity of the moving contact line [2, 3]. The first goal of the present is to provide evidence for slip flow near a moving contact line using high-resolution PIV experiments. The experiments reveal the presence of variable slip in the vicinity of the moving contact line and no slip further away, thus offering a direct pathway for the resolution of the moving contact line paradox. The second goal of the study is to examine the effect of dynamic hysteresis on the flow field. In the absence of hysteresis, the flow field in experiments is found to be in excellent agreement with theory. But higher values of hysteresis can have a dramatic effect on the flow field. Hysteresis induces a high-frequency fluctuation at the contact line due to the localised ‘stick-slip’ motion. The effect of this fluctuation is investigated in the present study using experiments and numerical simulations.

[1] Huh, C. & Scriven, L. E., Hydrodynamic model of steady movement of a solid/liquid/fluid contact line. J. Coll. Int. Sci., 35(1), 85-101 (1971)

[2] Cox RG., The dynamics of the spreading of liquids on a solid surface. Part 1. Viscous flow, J. Fluid Mech., 168, 169-194, (1986)

[3] Kirkinis E, Davis SH, Moffatt vortices induced by the motion of a contact line. J. Fluid Mech.,746:R3 (2014)