James Gilchrist, associate professor of chemical engineering, watches Cheerios converge in a bowl of milk. The oats attract each other to reduce the milk’s surface energy, a phenomenon called the “Cheerios effect” that explains other examples of self-assembly. Something similar — “the coffee ring effect” — occurs when a drop of coffee dries into a ring instead of a spot.
Gilchrist observes these effects at the nanoscale where arrays of nanoparticles self-assemble. He and Prof. Nelson Tansu of electrical and computer engineering are trying to learn how minute particles deposit themselves into optical coatings. Their work has led to development of LEDs that are three times brighter.
Gilchrist also collaborates with Profs. Xuanhong Cheng of materials science and engineering and Mark Snyder of chemical engineering to fabricate membranes for improving separation devices that monitor HIV infection as well as molecular separations of high-value chemicals produced by biorefineries.
Snyder and Gilchrist have formed a company to develop nanoscale coatings and dye-support anodes to enhance dye-sensitized solar cells (DSSCs). Reversing the engineering of the LED project (engineers want to get light out of LEDs but into solar cells), they are flipping the microlens array inside the solar cell device and using dye molecules instead of silicon to absorb light. Solar cells with internal microlenses have proven to be 30 percent more efficient.
A $1.1 million NSF grant is helping Gilchrist and his colleagues develop two processes that enable commercial scale-up of these products. Both utilize roll-to-roll technology, similar to high-speed newspaper printing, to produce monolayer particle coatings that self-assemble into well-ordered arrays as they are being deposited.
With Snyder and Prof. Jeetain Mittal of chemical engineering, Gilchrist is studying fundamental deposition and developing numerical models, respectively. Process development is done with Versatilis, a Vermont company that manufactures advanced electronics for solar, lighting, display and related markets.
“In the 1980s,” says Gilchrist, “scientists began to understand the underlying physics of particle interaction and deposition. “Today, we are learning to manipulate fluid properties to control the process more efficiently, which can lead to high-rate precision commercial processes. We hope these processes become the benchmark for others.”