Harish N. Dixit (IITH Hyderabad)

Moving Contact Lines: singularity, flow fields, hysteresis, and new insights from experiments

A moving contact line (MCL) forms when an interface between two immiscible fluids intersects a solid surface, a phenomenon encountered in everyday scenarios such as water drops sliding down a windowpane, spreading of paint on a dry wall, or ink-jet printing. What makes this problem fascinating is the singularity that arises at the moving contact line when the conventional no-slip boundary condition is applied to the moving solid. A significant portion of experimental work on MCL has primarily focused on elucidating the angle-versus-speed relationship, with limited attention paid to the flow patterns.

Following a concise introduction to this classical problem in fluid mechanics and the key outstanding questions to address, I will share my journey with this problem. The talk will discuss results from an experimental campaign involving a wide variety of fluid combinations, contact line speeds, and solid wettability. These experiments allow us to test theoretical models in unprecedented ways than ever before. A common strategy employed in theory to resolve the contact line singularity is to impose a slip near the MCL. Our experiments have found evidence for slip near a contact line, and these insights provide a pathway into how Nature resolves the singularity. I will also discuss some preliminary findings about the potential role of dynamic hysteresis in contact angles to alter flow fields.