Explore the fascinating world of liquid-liquid-solid interactions as researchers uncover the intricate dance of viscous and surface tension forces at the contact line. Discover how these findings challenge traditional models and open new doors for understanding fluid dynamics.
On the Breaking of a Liquid-Liquid Contact Line
The archetypal image of a liquid-gas moving contact line on a solid surface in motion, which many of us are likely to have already seen at some point, is as follows: a raindrop being driven around by the wind as it slowly inches along the surface of a glass windshield. The bimodal interaction has been thoroughly investigated and provides insight into the trade-off between viscous forces and surface effects.
Enter a team of researchers from the Indian Institute of Technology Hyderabad, who describe just such a situation: the motions of a contact line produced at the interface between two immiscible liquids and a solid. This new frontier provides a new direction for fluid mechanics and suggests a method of imposing boundary conditions that cannot be mathematically defined.
Unraveling the Mysteries of Liquid–Liquid–Solid Interaction
So the researchers designed a neat experiment to test this idea in an actual system. They set up a rectangular tank containing two layers of liquid – sugar water below and silicone oil above it — both of which have densities close to one another but different by nearly a factor of 1,000 in viscosity. The researchers were able to slide a glass slide vertically, at the turn of the tank, to form a moving contact line.
By using a method that follows small particles added to the liquids and lit with laser light, the researchers could map for the first time both sides of the liquid-liquid interface surrounding them while they moved the glass slide. What followed was just as puzzling: the flow velocities began to drop off quickly at a small distance from the contact line, and the liquid interface appeared to slide over the top of a sliding glass slide rather than be pinned there — resolving that seeming “singularity” in models of solvent to which observes must apply a no-slip boundary condition for the moving wall.
Conclusion
These results can be useful in addressing theoretical models of contact line dynamics and providing benchmarks for numerical simulations of liquid-liquid interfaces with this low viscosity difference. This work unveils the rich dance between forces that happens at the liquid-liquid-solid interface, offering new opportunities for flushing out a more detailed picture of fluid dynamics and its applications in engineering and biology alike.
