10:00–11:00 am
GCIS E123 929 E. 57th Street, Chicago, IL
Interfacial structure behind a moving contact line
When a flat spatula is quickly inserted into a honey jar, its moving surface drags a thin layer of air into the honey. We discovered that such a simple process produces a surprising, characteristic structure in the thickness of this air layer with multiple thin flat triangular structures separated by much thicker regions. This structure is ubiquitous, robust, and suggestive of a new fluid mechanical instability. We will show our precise measurements or the air gap as well as an analytic understanding of its features that differs from classical theory.
We also explored the reverse process, where a flat solid substrate is pulled out of a liquid bath. In that case, a liquid film is dragged up by the solid and a similar structure of thin and thick regions of liquid is observed. To quantify the absolute film thickness of this layer, we developed a new interferometric method, combined with maximum likelihood data fitting. The measurements show that both the thin and thick film thicknesses scale with the capillary number, Ca, which is a balance between viscous drag and surface tension forces.