Ability to track nanoscale flow in soft matter could prove pivotal discovery
Breakthrough in analysis method will boost studying soft matter for many applications
For roughly 70 years, Play-Doh has been entertaining children with its moldable, squishy form. This familiar substance belongs to a broader category known as soft matter, which includes some foods (such as mayonnaise), 3D printer gels, battery electrolytes and latex paint.
Scientists from the U.S. Department of Energy’s (DOE) Argonne National Laboratory and the Pritzker School of Molecular Engineering at the University of Chicago report a groundbreaking advance for better understanding and improving the flow properties of soft matter at the atomic level (nanoscale). This advance depends upon a state-of-the-art technique called X-ray photon correlation spectroscopy (XPCS).
“Soft matter is easily deformed,” explained Matthew Tirrell, a senior advisor and senior scientist at Argonne and an emeritus professor at the University of Chicago. “Its properties are highly responsive to outside stimuli, such as a force, temperature change or chemical reaction.”
Tirrell gave paint as an example. When paint is applied to walls, highly complex flows occur at the nanoscale, but when the brushing or rolling is stopped, one wants flow to stop so the paint does not drip down the wall.
“In a nutshell, we developed a new technique to characterize the complicated fluctuations that soft matter nanoparticles undergo while being subjected to something like an applied force or temperature change,” said graduate student and lead author HongRui He, who worked on this project as part of the Graduate Research Cooperative program. In this program, he is pursuing his Ph.D. at the University of Chicago while conducting his research at Argonne.
Until now, no one has been able to precisely determine the flow behavior and interactions of these nanoparticles over time and correlate them with the bulk flow properties. “Previous XPCS experiments required averaging collected data, which led to the loss of crucial information about the complex processes at the nanoscale,” noted Wei Chen, an Argonne chemist.
The team’s innovative method allows scientists to determine a key factor, the transport coefficient, based on XPCS data. This coefficient measures the flow in a material. Determining it is essential to understanding how soft matter moves and changes over time in response to an external stimulus.
To gain the needed XPCS data requires a special X-ray beam like that available at the Advanced Photon Source (APS), a DOE Office of Science user facility at Argonne. This beam is sensitive to any disorder in the material over time at the nanoscale.
The team tested their XPCS method with a complex soft material — a dense mixture of spherical charged particles in a salt solution. Shearing was the force applied to the material at beamline 8-ID-I of the APS. “Shearing occurs when you spread thick lotion on your hands and rub them together,” explained Suresh Narayanan, a physicist and group leader at the APS.
The shearing results provided valuable insights into the changing flow properties and deformities in this salt-containing mixture. At the start, three bands of nanoparticles formed: fast moving, slow moving and static. After 15 seconds, the fast-moving band vanished. About 40 seconds later, the three bands returned. These findings are beyond the reach of current analysis methods and mark a major leap forward for XPCS analysis relevant to many different types of soft matter.
“This XPCS development is very timely for future work due to the significant increase in beam brightness with the APS upgrade,” said Narayanan. “What’s more, it holds potential for studying natural phenomena, such as landslides, earthquakes and the growth of plaque in arteries. Understanding these fluctuations in flow at the nanoscale could help predict future changes on a larger scale.”
The in-progress upgrade to the APS includes a brand-new suite of beamlines at 8-ID dedicated to XPCS. The new beamlines will make use of the improved X-ray beam to enhance XPCS research going forward. New experiments are expected to begin at the upgraded APS later in 2024.
The team used the Center for Nanoscale Materials, another DOE Office of Science user facility at Argonne, to characterize the particles in the salt solution.
This research first appeared in PNAS. In addition to He, Tirrell, Chen and Narayanan, the Argonne and University of Chicago team included Heyi Liang, Miaoqi Chu, Zhang Jiang and Juan de Pablo.
The research was funded by the DOE Office of Basic Energy Sciences and the Laboratory Directed Research and Development program at Argonne.
About Argonne’s Center for Nanoscale Materials
The Center for Nanoscale Materials is one of the five DOE Nanoscale Science Research Centers, premier national user facilities for interdisciplinary research at the nanoscale supported by the DOE Office of Science. Together the NSRCs comprise a suite of complementary facilities that provide researchers with state-of-the-art capabilities to fabricate, process, characterize and model nanoscale materials, and constitute the largest infrastructure investment of the National Nanotechnology Initiative. The NSRCs are located at DOE’s Argonne, Brookhaven, Lawrence Berkeley, Oak Ridge, Sandia and Los Alamos National Laboratories. For more information about the DOE NSRCs, please visit https://science.osti.gov/User-Facilities/User-Facilities-at-a-Glance.
About the Advanced Photon Source
The U. S. Department of Energy Office of Science’s Advanced Photon Source (APS) at Argonne National Laboratory is one of the world’s most productive X-ray light source facilities. The APS provides high-brightness X-ray beams to a diverse community of researchers in materials science, chemistry, condensed matter physics, the life and environmental sciences, and applied research. These X-rays are ideally suited for explorations of materials and biological structures; elemental distribution; chemical, magnetic, electronic states; and a wide range of technologically important engineering systems from batteries to fuel injector sprays, all of which are the foundations of our nation’s economic, technological, and physical well-being. Each year, more than 5,000 researchers use the APS to produce over 2,000 publications detailing impactful discoveries, and solve more vital biological protein structures than users of any other X-ray light source research facility. APS scientists and engineers innovate technology that is at the heart of advancing accelerator and light-source operations. This includes the insertion devices that produce extreme-brightness X-rays prized by researchers, lenses that focus the X-rays down to a few nanometers, instrumentation that maximizes the way the X-rays interact with samples being studied, and software that gathers and manages the massive quantity of data resulting from discovery research at the APS.
This research used resources of the Advanced Photon Source, a U.S. DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.
Argonne National Laboratory seeks solutions to pressing national problems in science and technology by conducting leading-edge basic and applied research in virtually every scientific discipline. Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science.
The U.S. Department of Energy’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit https://energy.gov/science.