Voids, or empty spaces, exist inside matter in any respect scales, from the astronomical to the microscopic. In a brand new study, researchers used high-powered microscopy and mathematical theory to unveil nanoscale voids in three dimensions. This advancement is poised to enhance the performance of many materials used in the house and within the chemical, energy and medical industries — particularly in the world of filtration.
Magnification of common filters used in the house shows that, while they appear like a solid piece of fabric with uniform holes, they are literally composed of thousands and thousands of randomly oriented tiny voids that allow small particles to go through. In some industrial applications, like water and solvent filtration, paper-thin membranes make up the barriers that separate fluids and particles.
“The materials science community has been aware of those randomly oriented nanoscale voids inside filter membranes for some time,” said Falon Kalutantirige, a University of Illinois Urbana-Champaign graduate student. “The issue was that the complex structure of the membrane as a complete — which looks like nanoscale mountain ranges when magnified — was blocking our view of the void spaces. Because we couldn’t see them, we couldn’t fully understand how they affected filtration properties. We knew that if we could discover a strategy to see them, we could then work out how they work and ultimately improve filter membrane performance.”
The study, directed by Illinois materials science and engineering professor Qian Chen and University of Wisconsin-Madison professor Ying Li, is the primary to integrate materials science and a mathematical concept called graph theory to assist image and map out the random placement of those voids inside filtration materials. The findings are published within the journal Nature Communications.
Constructing on a previous study that used laboratory models, the researchers said the brand new study focuses on much more complex membranes utilized in industrial applications.
“The surfaces of the membranes we studied on this work look flat to the naked eye, but once we zoomed in using transmission electron microscopy, electron tomography and atomic force microscopy, we could observe these voids nestled inside these nanoscale mountainous landscapes that we call crumples,” said Kalutantirige, the study’s first creator.
Nonetheless, the team needed a method to measure and map these features to construct a quantitative predictive model and gain a more holistic picture of the membrane surfaces.
“Mapping and measuring alone will work for materials with a daily or periodic structure, making it mathematically easy to scale up our models and predict how structural properties will influence the fabric’s performance,” Chen said. “However the irregularity we observed in our study pushed us to make use of graph theory, which supplies us a mathematical strategy to describe this heterogeneous and messy — but practical — material.”
Graph theory helped the team finally gain a more holistic understanding of the filter membrane structure, which led them to find a powerful correlation between the unique physical and mechanical properties of random empty space and improved filtration performance.
“Our method is a really universal technique for describing materials,” Kalutantirige said. “Many things we use in on a regular basis life and science are usually not product of materials composed of repetitive uniform structures. So, the fantastic thing about the strategy, I feel, is that we are able to capture the ‘regularness’ of irregular structures.”
The team said that this advancement will improve the effectiveness of many next-generation porous materials, akin to polymers utilized in drug delivery.
“The title of this study hints on the concept of ‘beyond nothingness,’ and by that, we mean that these empty, void spaces are really necessary relating to developing one of the best filtration membranes,” Chen said. “This work is barely possible with our wonderful team of collaborators. Xiao Su helped us with the membrane performance testing. Emad Tajkhorshid, Charles Schroeder and Jeffrey Moore worked with us on the synthesis and evaluation of the polymer systems.”
