Solving friction problems could save U.S. millions of dollars

Saving millions of dollars in energy costs. Preventing blood clots. Extending the life of concrete. These are some of the potential applications of Michael Nosonovsky’s research into friction and wetting. The professor of mechanical engineering makes these topics interesting even to the neophyte.

When you ask Nosonovsky why we should care about friction, for example, he may mention the 2010 recall of 7.5 million Toyota cars that cost the company about $4.4 billion. The problem was that the pedal could get stuck in the accelerator position when the driver removed his foot. One possible reason for the flawed design? Toyota engineers may have modeled friction improperly.

“The classical model for the theory of friction has existed for a long time, but it doesn’t fully account for dynamic effects,” says Nosonovsky. “That’s why new fundamental theories are also highly relevant for applied work.”

Nosonovsky has been fascinated by friction, the resistance that results from one surface moving over another, for more than 20 years. An estimated 10 to 20 percent of energy in developed countries is spent on overcoming it, and a more careful application of tribology—the science of friction, wear and lubrication—might save us millions of dollars.

But much progress has been made already. Two decades of car engine research have produced advanced surface texturing technology for reducing engine friction, Nosonovsky says—even though the goal of a frictionless car engine may remain elusive.

The second focus of Nosonovsky’s research is wetting, which describes the physical and chemical interactions between liquids and surface roughness. This includes the design of omniphobic surfaces that repel not only water, but also various types of oils.

“Due to its non-polar molecules, oil has greater surface energy than water and it’s much more difficult to design surfaces that repel organic liquids, compared to making hydrophobic surfaces that push off water,” Nosonovsky explains. “But inspiration from nature has been very helpful for developing biomimetic liquid-repellant surfaces.”

A frequently cited natural example is the lotus effect, which refers to the self-cleaning properties of the lotus flower’s leaves. Thanks to wax-coated nanostructures on the surface of these leaves, dirt particles are conveniently picked up by water droplets.

Omniphobic surfaces are of interest for many diverse fields Nosonovsky has worked on with collaborators. In medicine, they help prevent blood from clotting in vessels that contain a catheter or stent. In the construction business, superhydrophobic concrete extends the lifespan of structures and pavements by reducing water penetration, the main cause of concrete deterioration over time.

In another project, Nosonovsky has designed corrosion-resistant coatings for the inside surface of metallic water pipes—a project of particular interest for a freshwater hub like Milwaukee. He also studies how vibrations from acoustic devices can separate solids from liquids or control liquid flow.

“Mathematically, high-frequency acoustic vibrations, which are structured across time, are similar to micro-scale surface roughness, which has a spatial structure,” Nosonovsky explains. “That’s why we can use vibrations, instead of chemicals, to control certain properties of pipes, ships and other freshwater applications.”