Decoding a Material’s ‘Memory’

by Erica K. Brockmeier

A suspension of particles of different sizes during shearing experiments conducted in the lab of Paulo Arratia, with arrows indicating particle “flow” and trajectories. In a new study published in Nature Physics, researchers detail the relationship between a disordered material’s individual particle arrangement and how it reacts to external stressors. The study also found that these materials have “memory” that can be used to predict how and when they will flow. (Image: Arratia lab)

New research published in Nature Physics details the relationship between a disordered material’s individual particle arrangement and how it reacts to external stressors. The study also found that these materials have “memory” that can be used to predict how and when they will flow. The study was led by Larry Galloway, a Ph.D. student in the lab of Paulo Arratia, and Xiaoguang Ma, a former postdoc in the lab of Arjun Yodh, in collaboration with researchers in the labs of Douglas Jerolmack and Celia Reina.

A disordered material is randomly arranged at the particle-scale, e.g. atoms or grains, instead of being systematically distributed—think of a pile of sand instead of a neatly stacked brick wall. Researchers in the Arratia lab are studying this class of materials as part of Penn’s Materials Research Science & Engineering Center, where one of the program’s focuses is on understanding the organization and proliferation of particle-scale rearrangements in disordered, amorphous materials.

The key question in this study was whether one could observe the structure of a disordered material and have some indication as to how stable it is or when it might begin to break apart. This is known as the yield point, or when the material “flows” and begins to move in response to external forces. “For example, if you look at the grains of a sand castle and how they are arranged, can I tell you whether the wind can blow it over or if it has to be hit hard to fall over?” says Arratia. “We want to know, just by looking at the way the particles are arranged, if we can say anything about the way they’re going to flow or if they are going to flow at all.”

While it has been known that individual particle distribution influences yield point, or flow, in disordered materials, it has been challenging to study this phenomenon since the field lacks ways to “quantify” disorder in such materials. To address this challenge, the researchers collaborated with colleagues from across campus to combine expertise across the fields of experimentation, theory, and simulations.

Read the full story in Penn Today.

The authors are Larry Galloway, Erin Teich, Christoph Kammer, Ian Graham, Celia Reina, Douglas Jerolmack, Arjun Yodh, and Paulo Arratia from Penn; Xiaoguang Ma, previously a postdoc at Penn and now at the Southern University of Science and Technology in Shenzhen, China; and Nathan Keim, previously a postdoc at Penn and now at Pennsylvania State University.

Arjun Yodh is the James M. Skinner Professor of Science in the Department of Physics and Astronomy in Penn’s School of Arts & Sciences and a member of the Penn Bioengineering Graduate Group.

Paulo Arratia is a professor in the departments of Mechanical Engineering and Applied Mechanics and Chemical and Biomolecular Engineering in the School of Engineering and Applied Science at the University of Pennsylvania.

Douglas Jerolmack is a professor in the Department of Earth and Environmental Science in Penn’s School of Arts & Sciences and in the Department of Mechanical Engineering and Applied Mechanics at Penn Engineering.

Celia Reina is the William K. Gemmill Term Assistant Professor in the Department of Mechanical Engineering and Applied Mechanics at Penn Engineering.

New Grant Aims to Broaden Participation in Cutting-Edge Materials Research

University of Puerto Rico’s Edgardo Sánchez (left) and Penn graduate Zhiwei Liao working in the lab of Daeyeon Lee. Via the Advancing Device Innovation through Inclusive Research and Education program, researchers from Penn and the University of Puerto Rico will continue their materials science collaboration while supporting STEM career pathways for underrepresented groups. (Image credit: Felice Macera).

The National Science Foundation (NSF) has awarded grants to eight research teams to support partnerships that will increase diversity in cutting-edge materials research, education, and career development. One of those teams is Penn’s Laboratory for Research on the Structure of Matter (LRSM) and the University of Puerto Rico (UPR), whose long-running collaboration has now received an additional six years of support.

With the goal of supporting partnerships between minority-serving educational institutions and leading materials science research centers, NSF’s Partnership for Research & Education in Materials (PREM) program funds innovative research programs and provides institutional support to increase recruitment, retention, and graduation by underrepresented groups as well as providing underserved communities access to materials research and education.

‘Research at the frontier’

With this PREM award, known as the Advancing Device Innovation through Inclusive Research and Education (ADIIR) program, researchers from Penn and UPR’s Humacao and Cayey campuses will conduct research on the properties of novel carbon-based materials with unique properties, and will study the effects of surface modification in new classes of sensors, detectors, and purification devices.

Thanks to this collaboration of more than 20 years, both institutions have made significant scientific and educational progress aided by biannual symposia and regular pre-pandemic travel between both institutions before the pandemic, resulting in a rich portfolio of publications, conference presentations, patents, students trained, and outreach programs.

“Together we have been publishing good papers that have impact, and we’ve really cultivated a culture of collaboration and friendship between our institutions,” says Penn’s Arjun Yodh, former director of the LRSM. “Our goal is to carry out research at the frontier and, in the process, nurture promising students from Puerto Rico and Penn.”

Ivan Dmochowski, a chemistry professor at Penn who has been involved with PREM for several years, says that this program has helped his group connect with experts in Puerto Rico whose skills complement his group’s interests in protein engineering. Dmochowski has also hosted UPR faculty members and students in his lab and also travelled to Puerto Rico before the pandemic to participate in research symposia, seminars, and outreach events.

“I’ve had students who have benefitted from being a co-author on a paper or having a chance to mentor students, and the faculty we’ve interacted with are exceptional,” Dmochowski says. “There’s a lot of benefit for both me and my students, and I’ve enjoyed our interactions both personally and scientifically.”

Penn’s Daeyeon Lee, a chemical and biomolecular engineering professor who has been involved with PREM for several years, regularly hosts students and faculty from UPR while working on nanocarbon-based composite films for sensor applications. The success of this collaboration relies on unique materials made by researchers at UPR combined with a method for processing them into composite structures developed in Lee’s lab.

“What I really admire about people at PREM, both faculty and students, is their passion,” says Lee. “I think that’s had a really positive impact on my students and postdocs who got to interact with them because they got to see the passion that the students brought.”

Read the full story in Penn Today.

Daeyeon Lee is a professor and the Evan C Thompson Term Chair for Excellence in Teaching in the Department of Chemical and Biomolecular Engineering and a member of the Bioengineering Graduate Group in Penn’s School of Engineering and Applied Science.

Arjun Yodh is the James M. Skinner Professor of Science in the Department of Physics & Astronomy in Penn’s School of Arts & Sciences and a member of the Bioengineering Graduate Group in Penn’s School of Engineering and Applied Science.

Arjun Yodh Named 2021 Michael S. Feld Biophotonics Award Recipient by The Optical Society

Arjun Yodh, Ph.D.

The Department of Phsyics in the Penn School of Arts & Sciences has announced that Arjun Yodh, Professor in Physics and Astronomy and member of the Bioengineering Graduate Group, was awarded the 2021 Michael S. Biophotonics Award by the Optical Society (OSA):

“He was selected for his ‘pioneering research on optical sensing in scattering media, especially diffuse optical and correlation spectroscopy and tomography, and for advancing the field of biophotonics through mentorship.’

The award ‘recognizes innovative and influential contributions to the field of biophotonics, regardless of career stage.'”