Peculiar things happen at the boundaries between liquids and solids.
At the interface between neatly ordered solid molecules and the more chaotic constituents of a liquid is a region where the rules that govern each individual substance don’t strictly apply.
A better understanding of how molecules behave at interfaces could help engineers solve a whole host of problems for the modern world. For example, interfaces are important for batteries, solar cells and many other energy storage and generation devices.
“Starting with the basic questions about why something happens at the molecular level often leads to something surprising or interesting that we can follow through to design or create materials,” says Matt Gebbie, who joined the University of Wisconsin-Madison in December 2019 as an assistant professor of chemical and biological engineering.
Gebbie plans to initially focus his research at UW-Madison on interfaces where the fluid component carries a charge—so-called electrolytes. These types of junctions are widely found in our devices and in our environment, including inside fuel cells, batteries and even the sticky slime that adheres barnacles to boats.
Ionic liquids are electrolytes that are made entirely out of charged ions and “are an especially interesting type of electrolyte, because there’s a tremendous diversity of different structures we can design to make materials with unique properties,” says Gebbie.
One example use for ionic liquids is in electrocatalytic devices that use renewable electricity to drive the conversion of carbon dioxide into fuels and chemicals. Another application is as a replacement for the corrosive acids and flammable liquids inside batteries. The stability of ionic liquids could all but eliminate the risk of catastrophic flame-outs.
During his PhD studies at the University of California, Santa Barbara, Gebbie explored ionic liquids through a physics-focused lens. His research took him down some unexpected channels, including a side-project studying how marine mussels stick to rock surfaces in harsh saltwater environments.
Gebbie also helped overturn some long-held assumptions about the very nature of interfaces involving ionic liquids. His measurements revealed that the interfacial transition zone formed at the boundaries between charged surfaces and ionic liquids can be roughly 10 times thicker than researchers previously thought.
“That result was one of the things that got me super excited about the impact of science,” says Gebbie. “I could see how experiments we did in the small seaside town of Santa Barbara spawned discussions all over the world.”
After completing his PhD in 2016, Gebbie pursued a postdoctoral fellowship at Stanford University. There, he worked toward developing new tools and materials to study interfaces with exquisite sensitivity.
And his tools hinged on a material that many people find exquisite: diamond.
Lab-grown diamonds sometimes contain irregularities known as color-center defects. And while the imperfections might ruin an engagement ring, diamonds with color-center defects can be incorporated into advanced sensors, as well as quantum computers, thanks to their unique optical properties.
Before Gebbie could get started on creating diamond-based sensors, however, he needed to answer another basic question.
“We really had to understand, at the most basic level, why you can grow diamond in the first place,” says Gebbie.
Growing diamonds in the lab involves subjecting a feed gas to intensely powerful microwaves to yield a hot reactive plasma. It’s a high-temperature process, yet the first few steps of lab-grown diamond formation share surprising commonalities with a common low-temperature phenomenon: freezing water.
Those similarities occur in the first few moments of a diamond’s growth—a process called nucleation. And contrary to prior hypotheses, diamond nucleation doesn’t happen all at once; instead, nucleation occurs in multiple steps, similar to recent proposals for how ice crystals form.
That insight will allow Gebbie’s colleagues at Stanford to design and grow diamonds with specific color-center defects, tailored for use in quantum computers and sensors. But while diamonds might be forever, postdoctoral fellowships come to an end, and now, Gebbie’s research at UW-Madison will come full circle, with an initial focus on interfaces involving ionic liquids.
Some of the first questions Gebbie will be asking involve how the structures and dynamics of interfaces control chemical properties. And those insights will be important for tuning interfaces for use in energy storage or electrically driven chemical reactions.
He’s open to exploring other questions and materials, too, however, as he grows his lab and begins mentoring students.
“One of the cool things about being a faculty member is training students to ask important questions, and to pursue research that makes an impact,” he says.