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Liquid Crystals - Beyond Color Generation

Liquid crystals, common in electronic displays, have been found to exhibit remarkable properties beyond color generation. Research by the Osuji lab at the University of Pennsylvania revealed that under specific conditions, these molecules form complex networked structures of filaments and flattened discs, capable of transporting materials similar to biological systems. Phase separating liquids typically form spherical droplets, driven by surface minimization. This work demonstrates that the alignment of liquid crystals within these droplets can deform fluid interfaces, driving the formation of more complex architectures and emergent active dynamics. This discovery, published in PNAS, may lead to self-assembling materials and new cellular activity models.

The capabilities of digital artificial neural networks grow rapidly with their size. Unfortunately, so do the time and energy required to train them. By contrast, brains function rapidly and power-efficiently at scale because their analog constituent parts (neurons) update their connections without knowing what all the other neurons are doing; in other words, they update using local rules. Recently introduced analog electronic contrastive local learning networks (CLLNs) share this important property. However, unlike brains and artificial neural networks, their capabilities were limited and could not grow with size because they are linear. Here, we experimentally demonstrate that nonlinearity enhances machine-learning capabilities in an analog CLLN, establishing a paradigm for scalable learning systems.

Mark Licurse, the LRSM Director of Education & Outreach, has been awarded the prestigious Hatfield Award for Excellence in Teaching in the Lecturer and Practice Professor Track. The award recognizes Licurse’s outstanding ability to effectively communicate complex concepts, innovate in undergraduate instruction, and inspire students to excel in engineering and science.

An alumnus himself, Licurse earned his B.S.E and Ph.D. in Materials Science and Engineering from Penn in 2006 and 2013, respectively. The Hatfield Award further cements his role as an exceptional educator.

The annual Postdoctoral Speaker Award sponsored by the American Physical Society’s Topical Group on Statistical and Nonlinear Physics (GSNP) was won by Sam Dillavou, for his talk on “The Ensemble Peels the Onion: Emergent Learning Via Sequential Error Mode Reduction.” Sam’s work is part of IRG1 on Learning Metamaterials, in the lab of Doug Durian in collaboration with Andrea Liu and Mark Miskin.

Dr. Ashley Wallace, the LRSM Associate Director of Diversity & Student Engagement, coordinated the second iteration of Diversity Equity Engagement at Penn in STEM (DEEPenn STEM) weekend that took place in person October 6-8, 2023.   Aiming to diversify graduate-level programs and the global workforce through methodical recruitment and retention efforts, DEEPenn STEM was created specifically for those with limited access to resources and guidance for pursuing advanced degrees in the STEM fields.  It was designed to serve as an integral part of the STEM pathway for students to pursue summer research experiences (ex: REUs) at Penn and successfully transition into graduate school and/or STEM careers.  Not only showcasing the interdisciplinary nature of STEM-related graduate research at Penn, the event also addressed the unspoken rules and questions for prospective graduate students, providing participants with a “roadmap” to be successful in graduate school and related endeavors. Following a highly successful inaugural program in 2022, the program saw significant growth in expanding to 5 schools (Schools of Arts & Sciences, Engineering & Applied Science, Medicine, Nursing, and Veterinary Medicine), showcasing an even greater variety of pathways in STEM that Penn has to offer.  Sixty-nine (69) undergraduate students from universities and colleges across the USA participated in the 3-day program.  Key highlights include: keynote address delivered by Penn’s esteemed Provost Dr. John L. Jackson, dessert reception hosted by Dr. Valarie Swain-Cade McCoullum (Vice Provost for Student Engagement), remarks by Deans of each school, faculty research talks, instructional workshops, panel discussions, poster presentations, and a number of opportunities to network with current Penn faculty, staff, graduate students, and postdoctoral fellows.  The LRSM co-sponsored the event and supported the attendance of 5 students from our Partnership for Research and Education in Materials, with the University of Puerto Rico.

The Laboratory for Research on the Structure of Matter (LRSM) has secured an $18 million renewal grant from the National Science Foundation (NSF). The LRSM has been funded by the NSF for half a century, with the laboratory’s distinguished status as an NSF-Materials Research Science and Engineering Center (MRSEC) since its establishment in 1994. The generous infusion of $18 million is poised to fortify LRSM’s ongoing mission of conducting groundbreaking interdisciplinary research and fostering innovation. With this support, LRSM is well-positioned to drive forward its two new Interdisciplinary Research Groups (IRGs), focusing on the development of innovative materials capable of adapting to their surroundings and external stimuli, as well as the creation of tissue-like synthetic biomaterials constructed from cellular building blocks. These initiatives promise to open new frontiers in materials science, further solidifying LRSM’s standing as a beacon of pioneering research in the field.

We are sorry to report the passing of Dr. Gilbert J. Sloan on May 25, 2023. He was 94 years old and still a volunteer in the LRSM for ~15 years. Gil retired from DuPont in 1994, having started with the company in the Central Research Department in 1953, after a successful career, first as a senior research scientist and later as Manager of Analytical Services. In 1972-3 he spent a sabbatical year as a visiting scientist at University College, Wales with Prof. Sir John Meurig Thomas, former director of the Royal Institution and Chair of Chemistry at Cambridge University.

Philly Materials Day, a day-long science and engineering festival, returned to an in-person program this year on Saturday, February 11, 2023. More than 85 volunteers from 15 different LRSM-affiliated research groups combined forces with Drexel’s Materials Science and Engineering department to run a series of hands-on demonstrations for more than 600 attendees (K-12 students and their families).

Charles J. McMahon, Professor Emeritus in the Department of Materials Science and Engineering, passed away on December 10, 2022, at the age of 89. Dr. McMahon earned a bachelor’s degree in Metallurgical Engineering in 1955 from the University of Pennsylvania and returned in 1963 for a postdoctoral fellowship in the newly formed Department of Metallurgy and Materials Science (now the Department of Materials Science and Engineering). He joined the faculty of that department, where he remained throughout his career. In addition, he was a member of the LRSM community and a valued participant in ARPA- and NSF-MRL block grants.

Dr. Ashley Wallace, the LRSM Assistant Director of Education and Outreach, coordinated the inaugural Diversity Equity Engagement at Penn in STEM (DEEPenn STEM) weekend that took place in person October 7-9, 2022. In an effort to address low representation of certain groups in science, technology, engineering and mathematics (STEM), DEEPenn STEM provided prospective graduate students from historically marginalized and traditionally underrepresented backgrounds with the resources to be successful in graduate school and related endeavors. Aiming to diversify graduate-level programs and the global workforce through methodical recruitment and retention efforts, DEEPenn STEM was created to serve as an integral part of the STEM pathway for students to pursue summer research experiences (ex: REUs) at Penn and successfully transition into graduate school and/or STEM careers.

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After a 2 1/2 year hiatus, the LRSM restarted its Science Café’s in Wilmington Delaware, with a presentation by Ottman Tertuliano on August 23rd. “Breaking Bones at the Nanoscale to Heal Them,” was quite a relatable topic with the, predominantly, older audience who were all too familiar with bone issues and repair. Ottman entertained, and enlightened those in attendance for 40 minutes, followed by questions from the captivated audience.

The LRSM Science Café’s began back in 2010, in collaboration with the PBS Nova series “Making Stuff” and had been going strong until February of 2020, when it, like many other in-person events, was paused during the pandemic.  Many of the talks have been captured over the years and can be streamed from our video archives page, including this month’s talk.

The 48^th meeting of the North American Thermal Analysis Society (NATAS) Conference met at Case Western Reserve University August 1-5, 2022.  A special session was held entitled the “Andrew McGhie Honorary” organized by Janis Matisons from Intertape Polymer Group.  McGhie has been a longstanding leader in NATAS, and his contributions to thermal analysis was rewarded by the Mettler Award in Thermal Analysis in 2011.  In 1992, McGhie was also awarded the NATAS Outstanding Service Award and became a NATAS Fellow in 1989. He is also a Past President of NATAS (2007).

If you squeeze very gently, no toothpaste comes out of the tube. Increase the force a bit and the toothpaste suddenly begins to flow. This transition from “no-flow” to “flow” is called yielding, and it is a ubiquitous feature of disordered materials (e.g., dense particle suspensions, foams & emulsions, and metallic glasses). A study led by Larry Galloway, a graduate student in Paulo Arratia’s lab, and Max (X.) Ma, a MRSEC alum from Arjun Yodh’s lab, provides new insights on how the evolution of the material micro-structure, quantified using the concept of excess entropy, can be used to predict this yielding transition in disordered materials. To do so, the team employed novel experimental methods (Galloway, Keim, Ma, Arratia, Jerolmack, and Yodh), numerical simulations (Teich, Graham, Kammer, Arratia, Jerolmack), and theory (Galloway, Celia Reina). The team found that the quantity excess entropy can be used to characterize the sample microstructure, as well as to develop a phenomenological model that captures flow quite well in both experiments and simulations in cyclically sheared dense colloidal systems. In particular, the team finds that the inception of flow (i.e., yielding) is marked by the material loss of memory.

Nature Physics article

Se-Um Kim, a postdoctoral researcher in Shu Yang’s lab, together with fellow postdocs, Young-Joo Lee and Dae Seok Kim, and graduate students Jiaqi Liu and Haihuan Wang, have developed a new photonic display platform via pneumatic inflation of thin membranes made from the main-chain chiral nematic liquid crystalline elastomers (MCLCEs), where the liquid crystal mesogens are arranged in a helix. By taking advantage of the large elasticity anisotropy and large Poisson’s ratio (> 0.5), the researchers geometrically program the size and the layout of the encapsulated air channels to achieve broadband color shift from near-infrared to ultraviolet wavelengths with less than 20 % strain perpendicular to the helical axis of MCLCEs. Each channel could be individually addressed as a color “pixel” to match with surroundings or to display 7-segment digits. It overcomes physical constraints in traditional photonic crystals made from isotropic materials. The large degree-of-freedom in the layout of the pixels and the air channels, together with unique mechanochromic performance of MCLCEs offers new insights to create new biomimetic, highly responsive and complex photonic devices with relatively simple operations.

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