Chemistry Seminar with Dr. Junsoo Kim from Northwestern University at 4:00pm

Abstract: Soft materials are used in emerging biomedical devices as well as high-volume applications such as tires. However, they break easily. The waste tires and their debris pollute the environment, and the low fracture resistance of soft materials makes their use in biomedical applications impractical. In this talk, I will discuss how the topology of polymer networks affects fracture properties such as toughness and fatigue resistance. Recently, we have shown that entanglements make polymer networks stiff, but not brittle. Thus, a polymer network in which entanglements outnumber crosslinks achieves both high modulus and toughness, overcoming long-standing modulus-toughness conflict. Such a topology enables high fatigue resistance, high strength, low friction, and high wear resistance. We have also shown that fatigue resistance can be further improved by deconcentrating the stress in the multiple length scales in particle-filled rubbers. The measured fatigue threshold is about 1,000 J/m2, which is a significant improvement given that the fatigue threshold of rubbers has been about 100 J/m2 since the first measurement in the 1960s.