An experimental study of flow patterns near a moving contact line

A contact line occurs at the intersection of a solid with two immiscible fluid phases, A and B. As a contact line moves, one fluid phase displaces the other fluid phase and consequently, flow patterns evolve in both the fluid phases. A moving contact line occurs in various applications like ink-jet printing, curtain coating, spray cooling, etc. and is thus of fundamental interest. Huh & Scriven developed a theoretical model in the viscous limit and reported three distinct flow fields in the two phases as a function of viscosity ratio and dynamic contact angle. The theory of Huh & Scriven(1971,JCIS) is incomplete since it results in a singularity at the contact line. Several models, either involving a precursor film or having slip at the contact line, have been proposed to alleviate the singularity. In particular, the slip-based model Kirkinis & Davis(JFM,2014) show a completely different flow field from that predicted by Huh & Scriven. Using careful experiments with different solid/fluid/fluid combinations, we present new PIV experiments with the aim of shedding new light on the flow fields in the vicinity of a moving contact line. These experiments complement the earlier experiments of Savelski et al.(1995,JCIS) and offer new insights into the physics of moving contact line.