A Study of Flow Patterns Near Moving Contact Lines Over Hydrophobic Surfaces

Understanding the flow patterns emerging near the contact line is a primary concern of moving contact line dynamics. A contact line occurs at the intersection of a solid surface with an interface between two immiscible fluids. The moving contact line dynamics can be observed in several flow phenomena, including inkjet printing, spreading of drops across a surface, and tertiary oil recovery, among others. Displacement of the contact line over the solid surface generates flow patterns in both the fluid phases. Based on flow kinematics and boundary conditions (Huh and Scriven, JCIS, 1971; Cox, JFM, 1986), two distinct flow patterns, a rolling motion and a split-streamline motion, occur in one of the fluid phases and the problem is primarily governed by viscosity ratio, \(\lambda\) , and dynamic contact angle, \({\theta }_{d}\) . Most of the existing experimental studies are for obtuse contact angles, \({\theta }_{d}\) > \({90}^{\circ }\) with very low viscosity ratio, \(\lambda \ll 1\) and at very low \(Re\) (Chen et al., JFM, 1997). The present study aims to obtain flow patterns at low to moderate values of \(Re\) and with a relatively higher viscosity ratio using a combination of experiments and simulations. We also present a comparison of our results to existing analytical models.