Hundreds of times thinner than a human hair, nanofibers can have a multitude of properties and applications, from biomedical engineering to water filtration to sensor technology. According to Margaret W. Frey, Fiber Science and Apparel Design, nanofibers are full of possibility. “We can vary their chemistry,” she says. “We can change the surface properties, their surface reactivity. We can make them conductive, piezoelectric.”
Frey specializes in making nanofibers and manipulating their properties. Then she finds interesting applications for them. Her group also experiments with coating cotton fabrics with nanofibers to transfer their unique properties to garments.
“The question I always ask myself is, who cares?” Frey says. “I can make this, but who cares? Then we collaborate with people all around campus and around the world to figure out where these nanofibers can make really interesting applications.”
What Nanofibers Can Do—from Fuel Cells to Filtration Systems
One of the advantages of nanofibers is that as the diameter of the fibers gets smaller and smaller, the surface-area to volume ratio goes up. “It all becomes surface,” Frey says. This makes nanofibers a tantalizing material for applications where compression is key—such as electronics or energy applications.
Frey and her students made nanofibers that could be an ideal material for smaller, more efficient electrodes. The group spun nanofibers from polyacrylonitrile, a polymer, and then manipulated them—burning everything off but the carbon and coating them with a conducting polymer.
With collaborators in Biological and Environmental Engineering, the team put the nanofibers into a fuel cell with special microbes that grow on the fibers. These microbes can digest pollutants from wastewater and create a current, transferring electrons to the nanofiber electrodes. Compared to the carbon cloth that’s currently available on the market, the nanofibers were able to conduct 38 percent more current with much less material.
“Eventually it means that you can make the fuel cells smaller,” Frey says. “One of the challenges here is to get enough of these cells that you can create some usable amount of current to actually power something.”
These nanofibers could bring researchers one step closer to being able to generate energy while filtering wastewater and to doing it more cheaply, as the efficiency of the nanofibers would bring costs down. “It was a first lab study that was quite promising and a good example of the kind of areas where this could be useful,” Frey says.
In other projects, Frey has manipulated the surfaces of nanofibers so they can filter pollutants from water themselves, attracting chemicals and pathogens as water passes through. In addition, she’s working on a quick process for electrospinning nanofibers from a very common polymer—the kind used in compostable cups—that can present biotin on the nanofiber surface. Biotin can then be used to capture specific proteins, a method which could be useful in blood tests or in the purification of liquids.
“There’s a whole lot of examples where we’ve made these different kinds of fibers and found different ways to functionalize them and use them to capture specific things, or interact with specific things, or release them with various stimuli, whether it’s temperature or pH,” Frey says.
Frey has worked extensively to make thermally responsive nanofibers—nanofibers that can become more or less absorbent at different temperatures. At a lower temperature, the materials in Frey’s lab absorb water or dye, and at a higher temperature, they can release it.
“This is a model for any application where we want to release a chemical with temperature at different rates,” Frey says.
Frey has taken the same polymers that make these nanofibers and applied them in a coating for cotton. “This changes the cotton from having its normal hydrophilic behavior to being more hydrophobic and allowing more water vapor to pass through,” she says. The Frey lab continues studies to tailor this change in the fabric’s behavior to happen around 32 degrees Celsius, or 90 degrees Fahrenheit. Once that temperature is reached, the cotton would ideally turn from being absorbent to being more water-repellant, wicking moisture away. This would be similar to fast-drying athletic garments currently available but without the shiny, clingy quality of polyester knits.
“Maybe we can get something that looks more like a cotton fabric but still has this comfort behavior,” Frey says. “It would potentially add a new material functionality and possibility be a different performance material than is currently available.”
In the course of their work, Frey’s group has developed new ways to see and study. For instance, they’ve made recent breakthroughs in studying cotton additives—the chemicals applied to our clothes. “Anything you buy that’s made of cotton has been treated so it will wrinkle less, but it’s not the greenest process,” Frey says.
“Anything you buy that’s made of cotton has been treated so it will wrinkle less, but it’s not the greenest process.”
Frey and her students wanted to see if they could apply a new, greener coating to cotton that would still have the same wrinkle-resistant effect, but they confronted a challenge. How would they confirm the chemical interactions on the surface of the cotton? Normally in molecular studies of cellulose (the molecule that makes up most of cotton), the cellulose is ground into a powder before nuclear magnetic resonance spectra (NMR) are measured. The grinding process also changes the structure of the cotton and additives.
“So my students just took the fabric and rolled it up and stuck it in the NMR tube,” Frey says. It worked. Frey’s students were able to measure both the chemical structure of the cellulose in the cotton, what crystalline form it was in, and also how the additives were attached to the cotton.
“You’re able to see that you’ve bonded these chemicals to the cotton, where on the molecule you’ve bonded them, and also whether it’s changed the cotton out of its native crystalline state,” Frey says. “It really provides information that we haven’t been able to get before.” Frey’s lab is conducting follow-up studies to explore the method and to use it to understand various reactions on the cotton’s surface.
What Industry Teaches
Frey earned her bachelor’s degree at Cornell, but before returning to Ithaca, she worked extensively in industry as well as obtained her PhD at North Carolina State University. Industry experience has allowed Frey to maintain a broad and relevant research program in academia.
“I was lucky in industry because I got to work with a really broad range of polymers, looking at processing them and characterizing them,” she says. “Natural polymers, synthetic polymers, and very high-performance and commodity polymers. I brought all of that experience with me.”
Frey’s time in industry also influenced the way she approaches teaching. “One example is when you’re working in industry, you’re almost always working in a team,” she says. “You’re working on projects where different people are taking different roles, all working toward the same goal. Whereas students sometimes feel reluctant to work in a team because they want control over their grade.”
Frey makes efforts in her courses to break that pattern—which is particularly appropriate in Fiber Science and Apparel Design, where students are interested in everything from industry management to fiber science to creative design. In her own work, Frey practices what she preaches, constantly seeking collaborations to extend the relevance of her work.
“At Cornell, there’s just this openness. People have a kind of freedom and the safety to try crazy things,” she says. “I think my favorite conversations are when I’m talking to a collaborator across campus, and we don’t understand a thing the other is saying—but we find one point of common ground where we can connect, and we have the confidence that it’s going to work.”