With the press of a button, researchers can use electric fields to assemble individual nanoscale particles into varying formations and ultimately alter their appearance. Penn State graduate students working in Professor of Chemistry Christine Keating’s lab are using this method to push the boundaries of nanoparticle science. Manipulating nanoscale particles using electric fields might just be the answer to creating revolutionary products to fix big problems.
One of these students, Nicole Famularo, explained how her research project was originally inspired by creating dynamic metamaterials, which are lab-made materials that have properties not generally found in natural materials. In this case, Famularo is working towards using nanoparticles to make a reconfigurable version of the invisibility cloaks demonstrated by collaborators in the lab of Douglas Werner, John L. and Genevieve H. McCain Chair Professor of Electrical Engineering. The idea is that this technology could be used, for example, to eliminate cross talk between antennas located in close proximity to one another. Albanie Hendrickson-Stives, another graduate student in the Keating lab, had the opportunity to chat with Famularo when she was a prospective graduate student. “I actually asked Nicole about the applications of her research and she told me about the antenna invisibility cloaking. I thought it was so cool, it got me interested in joining the lab,” she said.
Today, Hendrickson-Stives has worked with both microparticles and nanoparticles. By definition, microparticles can be as large as one millimeter and visible to the naked eye, however the largest nanoparticles are only one ten-thousandth of a millimeter in size. Like Famularo, Hendrickson-Stives also works with electric-field assemblies of particles. She is trying to create assemblies of particles with tunable optical properties, where she can manipulate fine changes in how the particles refract light by pairing them with solvents. This could lead to the development of precisely controllable sensors, lasers, and metamaterials.
So, what exactly are these nanosized particles? The physical properties of each nanoparticle are unique to the project’s end goal. Famularo’s research on cloaking signals uses particles with nanoscale stripes of gold of differing sizes and spacing, all encased in a porous silica shell that lets water diffuse freely. By varying the patterns, she can change the metallic and dielectric characteristics of the particles, which can alter how the particles respond to electric fields.
Hendrickson-Stives, on the other hand, focuses on visual manipulation and works with spherical particles made of acrylic glass in organic solvents because of how they interact differently with light. Changing the voltage and frequency of the electric field applied to the system alters how the particles assemble. Famularo notes the future possibility of working with Hendrickson-Stives on striped particle assemblies that could polarize light.
“An opal is a good example of the collective optical properties of an assembled group of particles because you can see many different diffracted colors of light from the glass particles,” said Hendrickson-Stives. “However, to see the individual particles, you’d have to use an optical or electron microscope.
Considering the tiny size of each particle and the instruments required to see them, it’s no big surprise that the field of nanoscience is on the frontier of research. However, both Famularo and Hendrickson-Stives noted that they weren’t exposed to the idea of working at the nanoscale until late in their academic careers.
“It’s a field that neither of us really learned about until grad school,” said Hendrickson-Stives.
Today, it’s common to find products at your everyday home goods or technology store that rely on nanoparticles being manipulated to produce varying colors. If you’ve recently walked by the television aisle, you’ve most likely seen QLED screens that use differing nanoparticle sizes to produce vibrant and changing colors. Famularo and Hendrickson-Stives also commented on their interest in how nanoparticles can potentially be used in other fields, such as nanomedicine, for radiation treatment and for understanding the effects of pollution in urban areas.
Both students noted that the research facilities and resources at Penn State played crucial roles in their decision to pursue a graduate degree at University Park, closely followed by the culture of support between advisers and graduate students. “Penn State has the multimillion-dollar Titan Krios microscope that can image samples at the atomic scale, and so few of these exist in the world,” recalled Famularo. “Knowing that the facilities were so cutting edge, I wanted to get to know more about the research at Penn State. Then I found out that Keating is part of the Center for Nanoscale Science where they get to do this cool research.”
The Center for Nanoscale Science is a Materials Research Science and Engineering Center (MRSEC), one of a network of centers located at academic institutions in the United States and supported by the National Science Foundation (see page 23). Students working in labs associated with the center have the chance to work collaboratively with peers in other colleges, who bring their own skill sets.
“It can be intimidating to talk to other scientists when you don’t know anything about what they study, but being able to collaborate on a day-to-day basis as part of the center makes it a lot easier to connect,” reflected Hendrickson-Stives.
Famularo added, “Our collaborators in electrical engineering have the computational and optical expertise that I don’t, and just by interacting with them I feel like I’m much less intimidated to think more about those fields.”
After graduation, Famularo is interested in working on nanomaterial coatings for space-bound crafts, while Hendrickson-Stives hopes to enter industry and create or improve on products that people can use every day.