Elastomers are widely used because of their large-strain reversible deformability. Most unfilled elastomers suffer from a poor mechanical strength, which limits their use. Using sacrificial bonds, we show how brittle, unfilled elastomers can be strongly reinforced in stiffness and toughness (up to 4 megapascals and 9 kilojoules per square meter) by introducing a variable proportion of isotropically prestretched chains that can break and dissipate energy before the material fails. Chemoluminescent cross-linking molecules, which emit light as they break, map in real time where and when many of these internal bonds break ahead of a propagating crack. The simple methodology that we use to introduce sacrificial bonds, combined with the mapping of where bonds break, has the potential to stimulate the development of new classes of unfilled tough elastomers and better molecular models of the fracture of soft materials.

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A simple model is proposed to predict the fiber diameter in electrospinning. We show that the terminal diameter is determined by the kinetics of the jet elongation—under the influence of the electric and viscous forces—and the solvent evaporation. Numerical and simple scaling analyses are performed, predicting the fiber diameter to scale as a power 1/3 of viscosity and 2/3 of polymer solution throughput divided by electrical current. Model predictions show a good agreement to our own electrospinning experiments on polyamide-6 solutions as well as to the data available in the literature.

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