A curious thing happens when wine is swirled around in a glass: a film coats the walls and the wine starts to climb as surface tension pulls the fluid together into droplets. Droplet-surface interactions depend on both the liquid and the surface, and mechanical engineer Alidad Amirfazli is looking at ways to measure their properties to help improve everything from medications to cooling systems.
Amirfazli is a researcher at the Vision: Science to Applications (VISTA) program at York University. He is taking advantage of smartphone cameras as a visual way to measure key information about surface tension.
“The product that we’ve been able to take to the market with the help of VISTA is a smartphone-based surface tensiometry system,” says Amirfazli.
“It is a system that by taking an image of a droplet, it allows (us) to get two different properties for a liquid. One is its surface tension, the second part of it is a measurement of contact angle.”
The first property, surface tension, describes a liquid’s tendency to act cohesively at its surface like a skin. It’s the reason why you can fill a glass a little bit past the top, and it will bulge past the rim and stay together without overflowing.
The second property, contact angle, measures how a liquid droplet behaves when it is in contact with a surface, and it’s a measure of whether the liquid tends to bead up or to spread out.
Understanding these interactions and being able to manipulate them has lots of applications. It can help make better paint formulations that spread evenly over a surface, or soaps that can remove more grease as they clean. Researchers might need to understand how pharmaceuticals that are delivered as pills interact with the stomach after they dissolve there, or how a repellent coating helps liquids bead away.
It could even help designers make smarter cooling systems by understanding how liquids spread over heat exchanging devices.
By taking advantage of commonly available devices like smartphones, Amirfazli is making these important measurements more accessible and energy efficient than the equipment used in most labs today.
No matter how curious a droplet-surface interaction may seem at first, a better understanding of their properties helps explain and predict behaviour so that we can design better products.
