Abstract- The fracture and fatigue of soft materials are tightly coupled to the topology of polymer networks. Achieving control over this topology and identifying the relation between topology and fracture/fatigue resistance are central to advancing the design of soft materials. In this talk, I will first review the importance of entanglement in the design of the elastic and fracture properties of polymer networks. Next, I will introduce two approaches that can engineer entanglements by mechanically and kinetically intervening in radical polymerization. Finally, I will discuss the molecular understanding of fracture-resistance dynamics in polymer networks. Specifically, I will show that UV light intensity influences entanglement formation in photopolymerized polymer networks. I will also discuss how applying mechanical stimuli via focused ultrasound during polymerization can control topology beyond thermodynamic equilibrium. These approaches are demonstrated using highly entangled hydrogels, which show significant differences in elastic and fracture properties due to the engineered polymer network topology. When a polymer topology is given, the toughness of polymer networks can be understood in terms of molecular structure. Through controlled material synthesis and the quantification of fracture resistance, we advance understanding of the time dependence of toughness in organogel and the fatigue threshold of LDPE thermosets. Our work expands the accessible design space for polymer network topology and offers new routes to tune mechanical response and fracture behavior in soft materials with molecular understanding.
Bio- Junsoo Kim is an assistant professor of Mechanical Engineering at Northwestern University. He earned his Ph.D. in the Material Science and Mechanical Engineering department at Harvard University in 2022, followed by postdoctoral training at Harvard University. Before joining Harvard in 2017, he was a researcher at Electronics Telecommunications Research Institute. He earned his M.S. in 2013 and B.S. in 2011 at Seoul National University. He has co-authored about 40 papers in peer-reviewed journals such as Science, Nature, Advanced Materials, etc, and has contributed to the field of mechanics of soft materials. He is selected as a Kavli Frontiers of Science Fellow by the National Academy of Sciences and Scialog Fellow by the Research Corporation for Science Advancement, and received the 9th Hanwha Non-Tenure Faculty Award from Hanwha Group and Haythornthwaite Foundation Research Initiation Grant.
Andrew Liguori
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