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Katelyn Kirchner, a doctoral candidate at Penn State, is on a research fellowship at Hokkaido University in Japan, where she works in a cleanroom to visualize the fluctuations in glass at the smallest possible scale. Credit: Courtesy Katelyn Kirchner.

From fiber optic cables to smartphones, glass is playing a major role in emerging technology. To learn more about how glass will shape future society, we spoke with Katelyn Kirchner, a doctoral candidate at Penn State, who is studying with John Mauro, Penn State’s Dorothy Pate Enright Professor of Materials Science and Engineering. Kirchner is lead author and Mauro corresponding author on a recent review article on the unique properties of glass published in the journal Chemical Reviews.

The article, which was published in print last month and co-authored with an international team of scientists, is the first comprehensive look at the spatial and temporal fluctuations of glass. It is a review of experimental, computational, and theoretical approaches to characterize and demonstrate the effects of various types of fluctuations on physical properties and processes, focusing primarily on commercially relevant oxide glasses.

Let’s start with the basics. What is glass?

That’s a wonderfully complicated question. The exact definition is something that is still being explored today. A glass is a non-equilibrium, non-crystalline state of matter that appears solid on a short time scale but continuously relaxes towards the liquid state. Let’s break that down a bit further. Glass is a nonequilibrium material, which means the atomic structure is not in it’s lowest energy, equilibrium configuration, which would be a liquid or crystal state. Consequently, all glasses have two options: to continuously relax toward the equilibrium liquid state or undergo a phase transition into the crystal state.

This relaxation to the liquid state is so slow that from the human observation time, glasses appear solid. Glass being non-crystalline means the atomic structure lacks a long-range pattern, which adds additional complications when trying to predict how the atoms will arrange. And there are many other scientific “non” words we could include to more accurately define “what is glass?” We understand glass by what it is not, but we do not yet fully understand what glass is. This complication makes it thrilling to be in the field of glass science, as there is so much left to explore.

Despite our lack of understanding of it, what are some of the ways the unique qualities of glass are being deployed in society today?

Think about all the ways we interact with glass in our daily lives, in areas like information technology, where glass is fundamental to displays, augmented reality, memory storage, and optical data transfer. Then there are areas like transportation and architecture, with vehicles and construction materials, or the energy sector with photovoltaics and next-generation batteries. You can even look to health care with pharmaceutical packaging, antimicrobial surfaces, and prescription lenses. The impact of glass on our world has been tremendous.

What are you currently working on?

Right now, I’m doing mostly experimental work trying to visualize the fluctuations in glass. By “fluctuations” I mean spatial fluctuations, how the properties vary in different regions of the glass, and I also mean temporal fluctuations, how the material changes over time.

One of the most fascinating things about glass is that these fluctuations (i.e., deviations) in the atomic structure directly impact the macroscopic properties. When I come back to Penn State from my research fellowship at Hokkaido University to complete my Ph.D. with Dr. Mauro, I will be working with the data I’m collecting now to develop a computational framework to better understanding how fluctuations in thin film glasses could be manipulated to achieve new-found property behaviors.  

What would be some of the potential applications for what you’re discovering?

Fiber optics is a good one, because if we understand fluctuations in glass, we can better understand, predict, and optimize how an optical signal moves through a cable. When you consider the long distances these signals travel, we’re talking about transoceanic communication, every small fluctuation has a big impact.

Each time the light signal hits the silica walls of the cable, the local properties of the glass are going to influence how that signal propagates through the rest of fiber, which impacts the quality of the signal transfer and overall cost of the infrastructure. A deep understanding of how the impact of fluctuations in glass has major potential to improve fiber optic technology, and this is just one example of a potential application.

What about the future? What new, future technology do you think will be facilitated by glass?

That’s the great part of this work. The possibilities are endless when we look toward applications of tomorrow for glass, such for the development and commercialization of non-lithium ion batteries, improved electronic memory storage devices, improved sustainable energy production, augmented reality interfaces, etc.

The purpose of materials research is to better understand the fundamental sciences so we can develop the next groundbreaking technologies, and I have no doubt glass will play an integral role in that future.

I remember as a kid my uncle, who was a metallurgist, showing me the images of the Hubble Space Telescope. He explained the engineering of the various materials used to facilitate the visualization of distant galaxies. Glass has allowed us to see beyond our own galaxy and explore the universe. It’s thrilling to think about all the future discoveries that will be made thanks to glass.

Other co-authors on the paper are Seong Kim, Karan Doss, Collin Wilkinson, Yongjian Yang, Rebecca Welch, and Matthew Mancini of Penn State; Daniel Cassar and Edgar Zanotto of Brazil’s Federal University of São Carlos; Madoka Ono of the Research Institute for Electronic Science at Hokkaido University; Mikkel Bødker and Morten Smedskjaer of Denmark’s Aalborg University; Shinji Kohara of Japan’s National Institute for Materials Science; and Longwen Tang and Mathieu Bauchy of the University of California at Los Angeles.

The Penn State work was funded in part by the National Science Foundation.