Fracture-resistant soft materials by topology engineering

Soft materials, also called elastomers and gels, are used in high-volume applications such as tires as well as in emerging biomedical devices. 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. We have shown that entanglements stiffen the polymer network but do not embrittle it. Consequently, a polymer network in which entanglements outnumber crosslinks achieves both high modulus and toughness, overcoming long-standing modulus-toughness conflict. This principle is based on the network structure, not chemistry, so it can be applied to various material systems and fabrication processes. Also, we have shown that the fatigue threshold of rubbers can be greatly improved by deconcentrating the stress at the crack tip by designing the molecular structure of 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.