Sitting in a restaurant, you reach for the ketchup bottle, eyeing the basket of fries in front of you. You give the bottle a shake, then a tap. For a moment, nothing happens \u2014 the ketchup clings stubbornly to the glass. Then, all at once, it lets go and rushes out, sometimes in a steady stream, sometimes in a messy surge that threatens to flood the basket.<\/p>\n
That awkward moment when ketchup stops behaving like a solid and suddenly starts flowing like a liquid is called\u00a0\u200b\u201cyielding.\u201d Scientists see the same kind of behavior in many everyday and advanced materials, from toothpaste, paints and concrete to 3D-printing inks and electrodes used in next-generation batteries<\/a>. Yet, what actually causes a material to hold its shape one moment and suddenly let go the next has been surprisingly hard to pin down, especially deep inside dense, opaque fluids where particle motion is difficult to see.<\/p>\n In a new study from researchers at the U.S. Department of Energy\u2019s (DOE) Argonne National Laboratory and the University of Chicago, scientists used powerful X-ray beams and sophisticated computing resources to track\u00a0\u200b\u201cketchup-like\u201d materials as they yielded and flowed. They found that tiny differences in how particles attract or repel each other can make a material flow smoothly, flow in uneven bands, or even stop flowing and turn solid again while under stress. The results could help engineers design better consumer products and more reliable manufacturing processes by precisely controlling when and how soft materials begin to flow.<\/p>\n \u201cYielding is the transition from solid-like behavior to liquid-like behavior,\u201d explained Argonne Assistant Physicist Hongrui He.\u00a0\u200b\u201cBy applying a force or stress, we are able to manipulate the state of matter. There is no perfectly solid or perfectly liquid material \u2014 everything is somewhere in between, and yielding is the shift from one to the other. Given enough time, even a mountain can behave like a very slow-moving fluid.\u201d<\/p>\n To study this transition, the team created two closely related materials, both made of tiny particles suspended in liquid. In one, the particles were prepared so they mostly repelled each other. In the other, the researchers added a salt solution that subtly altered the particles, so they were weakly attracted and tended to stick together.<\/p>\n At Argonne\u2019s\u00a0Center for Nanoscale Materials<\/a>, a\u00a0DOE\u00a0Office of Science user facility, the size, composition and surface charge of the samples were carefully characterized to ensure that any changes in flow behavior came from particle interactions rather than changes in the particles themselves.<\/p>\n When the samples were not under stress, they looked almost identical. The striking differences only appeared when the researchers applied force and watched how each material flowed.<\/p>\n \u201cWhen the particles repel each other, the material changes shape in a very even way,\u201d He said.\u00a0\u200b\u201cIt flows in a predictable way, without forming large weak spots inside.\u201d<\/p>\n The picture changed when the particles were made slightly attractive. In this case, the particles tended to clump together into dense regions, leaving behind pockets of empty space. Under stress, some parts of the material started to move while neighboring parts stayed stuck. The material split into\u00a0\u200b\u201cshear bands\u201d \u2014 regions that flowed at different speeds.<\/p>\n \u201cIn the attractive system, parts of the material are almost frozen while other parts are flowing,\u201d said Wei Chen, a chemist from Argonne and the University of Chicago.\u00a0\u200b\u201cThat leads to more complex behavior, such as delayed yielding and resolidification, which you do not see in simple fluids.\u201d<\/p>\n Delayed yielding occurs when a material resists flow for a while after a stress is applied and then suddenly begins to move. Resolidification is the opposite: the material flows for some time and then abruptly stops and behaves like a solid again, even though the applied stress has not changed. These effects help determine whether a material spreads smoothly in use or instead suddenly stiffens, leading to problems such as clogs in industrial processes.<\/p>\n To uncover what was happening inside the materials, the researchers combined standard rheology \u2014 measurements of how a material flows and changes under stress \u2014 with a technique called X-ray photon correlation spectroscopy (XPCS) at\u00a0beamline\u00a08-ID<\/a>\u00a0at the\u00a0Advanced Photon Source<\/a>, a\u00a0DOE\u00a0Office of Science user facility at Argonne. While rheology measurements revealed how the whole sample responded,\u00a0XPCS, which uses a very bright X-ray beam, allowed the team to track tiny fluctuations in scattered X-ray signals that revealed how groups of particles move over time.<\/p>\n \u201cThe unique aspect of our approach is that we can measure the motion of the small particles and the overall material response at the same time,\u201d Chen said.\u00a0\u200b\u201cThat allows us to directly connect microscopic dynamics to macroscopic behavior in real time.\u201d<\/p>\n Even with these tools, experiments alone cannot capture every detail of the particle motion. To fill in the picture, the team used computer simulations to model dense suspensions of many interacting particles under flow, making it possible to track the motion of individual particles. Simulations were performed on Bebop, a high performance computing cluster at Argonne\u2019s\u00a0Laboratory Computing Resource Center<\/a>.<\/p>\n \u201cIn experiments, the material is dense and opaque, so you can\u2019t track every single particle,\u201d said Heyi Liang, a research associate at Argonne and postdoctoral scholar at the University of Chicago.\u00a0\u200b\u201cWith simulation, you can. We built the simplest model that still captures the most important parts, including delayed yielding and resolidification. We then used it to understand what is happening at the boundaries between flowing and non\u2011flowing regions.\u201d<\/p>\n The simulations showed that weak junctions between shear bands \u2014 areas where particles are less well connected and have more room to move \u2014 play a key role. Under small stresses, these junctions hold, and the material creeps slowly. As stress continues, some junctions suddenly fail, allowing bands of particles to slip past each other, producing delayed yielding. As the system continues to evolve, new junctions form and lock the structure again, leading to resolidification.<\/p>\n By tying these microscopic events to measurable quantities from\u00a0XPCS\u00a0and rheology experiments, the team built a consistent picture that matched both experiment and simulation.<\/p>\n \u201cOur findings bridge the microscopic and macroscopic worlds of soft matter,\u201d said one of the study\u2019s coauthors, Juan de Pablo, New York University executive vice president for Global Science and Technology and executive dean of the Tandon School of Engineering.\u00a0\u200b\u201cBy directly visualizing how particles interact and reorganize as these materials yield, we can now connect nanoscale dynamics to large-scale mechanical behavior. This gives us a framework to design and tune the flow properties of soft materials with unprecedented precision.\u201d<\/p>\n The results of this research were published in the\u00a0Proceedings of the National Academy of Sciences<\/a>.<\/p>\n Other contributors to this work include Miaoqi Chu, Zhang Jiang and Suresh Narayanan from Argonne, and Matthew Tirrell from Argonne and the University of Chicago.<\/p>\n This study was funded by\u00a0DOE\u00a0Office of Science, Basic Energy Sciences.<\/p>\n \u00a0<\/p>\n Amber Rose\u00a0is a science writer and editor for Argonne specializing in coverage of chemical sciences and engineering, materials science, microelectronics and physics. She holds a master\u2019s degree in chemistry from the University of California San Diego. Rose joined Argonne in 2024 and has been a science writer for more than 3 years. She previously worked as a science writer for the University of Illinois Urbana-Champaign Grainger College of Engineering.<\/p>\n About Argonne\u2019s Center for Nanoscale Materials<\/p>\n The Center for Nanoscale Materials is one of the five\u00a0DOE\u00a0Nanoscale Science Research Centers, premier national user facilities for interdisciplinary research at the nanoscale supported by the\u00a0DOE\u00a0Office 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\u00a0DOE\u2019s Argonne, Brookhaven, Lawrence Berkeley, Oak Ridge, Sandia and Los Alamos National Laboratories. For more information about the\u00a0DOE\u00a0NSRCs, please visit\u00a0https:\/\/\u200bsci\u200bence\u200b.osti\u200b.gov\/\u200bU\u200bs\u200be\u200br\u200b-\u200bF\u200ba\u200bc\u200bi\u200bl\u200bi\u200bt\u200bi\u200be\u200bs\u200b\/\u200bU\u200bs\u200be\u200br\u200b-\u200bF\u200ba\u200bc\u200bi\u200bl\u200bi\u200bt\u200bi\u200be\u200bs\u200b-\u200ba\u200bt\u200b-\u200ba\u200b-\u200bG\u200blance<\/a>.<\/p>\n About the\u00a0Advanced Photon Source<\/p>\n The U. S. Department of Energy Office of Science\u2019s Advanced Photon Source (APS) at Argonne National Laboratory is one of the world\u2019s most productive X-ray light source facilities. The\u00a0APS\u00a0provides 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\u2019s economic, technological, and physical well-being. Each year, more than 5,000 researchers use the\u00a0APS\u00a0to 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.\u00a0APS\u00a0scientists 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\u00a0APS.<\/p>\n This research used resources of the Advanced Photon Source, a U.S.\u00a0DOE\u00a0Office of Science User Facility operated for the\u00a0DOE\u00a0Office of Science by Argonne National Laboratory under Contract No.\u00a0DE-AC02-06CH11357.<\/p>\n Argonne National Laboratory<\/a>\u00a0seeks 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\u00a0UChicago Argonne,\u00a0LLC<\/a>\u00a0for the\u00a0U.S. Department of Energy\u2019s Office of Science.<\/a><\/p>\n The U.S. Department of Energy\u2019s Office of Science\u00a0is 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\u00a0https:\/\/\u200bener\u200bgy\u200b.gov\/\u200bs\u200bc\u200bience<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"Sitting in a restaurant, you reach for the ketchup bottle, eyeing the basket of fries in front of…\n","protected":false},"author":2,"featured_media":424236,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7],"tags":[111,2055,139,69,147],"class_list":["post-424235","post","type-post","status-publish","format-standard","has-post-thumbnail","category-science","tag-new-zealand","tag-newswise","tag-newzealand","tag-nz","tag-science"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts\/424235","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/comments?post=424235"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts\/424235\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/media\/424236"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/media?parent=424235"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/categories?post=424235"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/tags?post=424235"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}