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ILP Institute Insider

January 9, 2013

Sticky Science

Finding out what "sticks" to revolutionize processes all across the industrial spectrum.

Eric Markowsky

“I like to play with my food,” admits MIT School of Engineering Professor of Innovation Gareth McKinley.

Gareth McKinley
Professor of Teaching Innovation
MIT School of Engineering
He explains: “As you play with your food, you experience the resistance. You experience how hard it is to smear something on a surface, whether it be mayonnaise or peanut butter. You experience the force that’s required to cause a certain kind of flow, and that’s exactly the same thing that you experience in industry.”

In addition to being the Associate Department Head for Research in Mechanical Engineering, Professor McKinley is also the primary investigator of the Non-Newtonian Fluid Dynamics Research Group, exploring the governing mechanics of fluids that exhibit complex microstructures, like most polymers and many foodstuffs.

“We think about things that are sticky, we think about things that are slippery or slimy,” McKinley says, but while most people appreciate concepts like sticky, slippery, or slimy in an intuitive sense, he and his research group strive to translate that intuitive understanding into mathematical models to develop new engineering and manufacturing processes.

“The field of polymer science and technology is extremely large,” McKinley says. “Almost all of them are processed in the liquid state. Whether we think about fabrics that we buy or films that we might put on walls or other surfaces, they all contain polymers.”

How much force should an inkjet printer use to deposit a clear image on the page? How large a pump does it take to coat a large surface with paint? How quickly can a spinning machine pull out a fiber feed without snapping it? Questions like these guide the work of the Professor McKinley’s research group across a wide variety of applications, from commercial bread production to collecting naturally desalinated water out of desert air.

It’s What’s on the Surface that Counts

“We are also very interested in interfacial engineering,” McKinley says. “What I mean by that is controlling the properties of a fluid when it contacts a solid or even a vapor.” By engineering a surface or a surface coating to interact with the properties of fluids in specific ways, McKinley and his research associates can control what happens at the point of contact.

Take his group’s work on “Fog Harvesting” for example. The Saudi Arabian peninsula is a vast natural desert sitting right next to a large natural saltwater body. “The sun heats the ocean, the water leaves the ocean,” McKinley describes, “and it comes away typically without a large part of its salt or its impurities. If we can control how that water actually condenses on a surface and then collect that, then you can think about farming or harvesting that water, and that’s like a natural, thermally driven desalination process.”

Collecting water would mean designing surfaces that are very water-attractive. For other applications, surfaces that readily repel water and other materials might be preferable. “We’re particularly interested in trying to do this on glass on a transparent surface,” McKinley says, “so you can develop glass coatings that improve the amount of light that’s transmitted but also prevent fouling by sand or biological deposits.”

Such a coating could have a significant impact on the efficiency of solar cells. “You want your solar cells to operate year-round,” McKinley says. “You want them to let as much light through as possible, but you also don’t want them to get dirty, so you’d like them to clean themselves ideally.”

At a larger scale, it might be possible to treat oceangoing or airborne vessels with a similar coating to lower frictional drag. It’s an idea with roots in the natural world. “If you feel the surface of a dolphin,” McKinley says, “it tends to be coated in a protein gel or a mucus gel, and that mucus gel is non-fouling, it prevents things from growing on the surface, but also makes the surface slipperier or lower friction. We’re interested in taking some of those ideas and maybe making a friction reducing coating for large objects.”

At every scale, McKinley’s interests lie in understanding the essential physics of the interactions between fluids and their surroundings in order to find the potential hiding in plain sight on the surface of our world.

A Fluid Lab

The Fluid Mechanics Laboratory in the MIT Department of Mechanical Engineering, home to the Non-Newtonian Fluid Dynamics Group, is set up a little bit differently from many other labs. “It’s one large lab that’s shared by about six faculty,” McKinley explains. “That’s something that’s been a part of our tradition since Asher Shapiro was the head of Mechanical Engineering in the late 1960’s. He espoused the idea that it shouldn’t be an individual professor in an individual lab. We should learn from each other, and we should try and share equipment, share ideas, share theories, share experiments.”

An open format contributes to an ethic of collaboration that extends beyond the Institute. McKinley says he and his students are particularly interested in collaborating with industry to continue developing super hydrophobic coatings for photovoltaic applications. “We’ve developed this technology, but what we’re really looking for is industrial partners that can help us scale it up,” he says. “MIT’s extremely good at developing new science and new processes. Industry’s extremely good at figuring out how to do that on a reliable basis, and that’s what we’re really keen on working with companies through for.”

McKinley encourages active and ongoing collaborations with industry. “In my experience the kind of industrial collaboration that works best is one where you have an equal partner on the other side,” he says. “It’s really important that you have someone who’s interested in the research, who’s willing to help guide the research. In some sense, if you just send money you don’t get the full return of what you should get by coming to MIT.”

What should industry get for collaborating with MIT? According to McKinley, three things. “Just like in real estate you learn that there are three important things, location, location, location, I think working with people at MIT it’s all about students, students, students,” he says. “Every year we have a fantastic influx of new students both at the undergraduate level and the graduate level, and they’re all keen to do something that impacts the world.”