Why do some drops of water stick to material surfaces while others don’t?

Young graduate student examines water droplets on material surfaces

Image: College of Engineering

Researchers in the College of Engineering at Texas A&M University are trying to understand why some water droplets adhere to material surfaces while others don’t.

Their research has applications in many industries, and the team hopes their findings have the potential to be applied to a variety of scenarios to improve the efficiency, safety and effectiveness of industrial machines and equipment.

“The underlying principle we are seeking to study with this is very commonplace and yet very complex,” said Sungyon Lee, an assistant professor in the Department of Mechanical Engineering. “On a rainy day, you can just look out the window and see the water droplets and wonder, ‘Why do some of the droplets run down the window and others don’t?’ We are studying ways to answer this fundamental concept because of the applications it can have elsewhere.”

Lee explains that this common phenomenon has applications in industries like transportation, oil and gas, engineering construction, color ink jet printing and many others. For example, a key challenge that faces aircraft engineers is that because of the altitude and speed at which aircraft operate, water droplets that remain on the wings during flight are able to freeze over on the wing and endanger the craft. Lee’s research can provide a better fundamental understanding of why droplets may still adhere to an aircraft wing in those conditions and allow designers and engineers to create the wings in such a way that the droplets will no longer stick, making the plane safer.

“It isn’t an easy question to answer,” Lee said “But if we take this scenario with a bunch of droplets on a wing surface and now you have wind pushing those droplets, it becomes even more complicated as the forces and factors that cause these phenomena are increased. It turns out that predicting that threshold between what makes a droplet stick and what makes it run off a surface is not trivial at all, so there are a lot of fundamental questions we can ask even in a simple scenario.”

Lee co-authored an article, “Droplet Depinning in a Wake,” which was published as a rapid communication in the journal Physical Review Fluids.

The research is part of a project funded by the National Science Foundation and is being co-investigated by Edward White, associate department head and associate professor in the Department of Aerospace Engineering.

More at the College of Engineering