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Using light to detect molecular forces, chemical bond scission and to understand fracture
Costantino Creton
Soft Matter Science and Engineering, ESPCI Paris, Université PSL, Paris, F
Recent advances in chemistry have made it possible to directly optically visualize forces on chemical bonds or even bond scission by using molecules that either emit light or become fluorescent when activated by the application of a force. Such chemical/optical, tools although experimentally challenging, can be invaluable to investigate how macroscopic forces translate into molecular forces and bond
scission. In this seminar after a brief introduction on the type of molecules and signal that can be obtained, we will focus on incorporation of the mechanophore into materials and how the optical signal can be reproducibly detected and quantified. Some examples on how this optical signal can be used to directly detect the macroscopic stress field or the damage to the material will be given. The
upscaling from the molecular scale to the macroscopic scale presents several challenges and experiments provide novel insight in both physics of polymers and the mechanics of fracture. We will discuss as an example the effect of temperature and rate on the fracture energy of elastomer and demonstrate that molecular bond breakage is far from limited to the interfacial plane and is highly sensitive to fracture conditions.