Toughening Elastomers with Sacrificial Bonds and Watching Them Break

Abstract

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.

Characterizing Large Strain Elasticity of Brittle Elastomeric Networks by Embedding Them in a Soft Extensible Matrix

“…The stiffening of the triple network is also well described for λ cor < 4. At higher elongation, the stress of the TN diverges however from the master curve suggesting a damage mechanism due to internal bond breakage [1] . which is not the focus of the present paper.…”

“…Given these restrictions, changing the monomer used to synthesize the stiff network appears to have a limited influence on the mechanical properties. The networks MA 1 , EA 1 and BA 1 have the same average molecular weight between crosslinks M x of 7500 g.mol -1 (from Table 4), but a number of repeat units N x between crosslinks which decreases with the molar mass of the monomer: N x = 86 for MA 1 , 76 for EA 1 and 59 for BA 1 .…”

“…In the absence of viscoelastic dissipation, the threshold fracture energy  0 of the elastomers is quantitatively explained by the sequential fracture of highly stretched elastic strands in the plane of the interface as the crack propagates. [1,5] To avoid this damage localization process leading to early fracture, it is possible to modify the network architecture to create additional energy dissipation mechanisms. Many strategies have been tried to increase the toughness of unfilled elastomers by network design.. [6] [7] [1,8] Our group has recently reported the successful design of multiple interpenetrating network elastomers through the sequential polymerization of acrylic monomers, in such a way that the network synthesized first becomes progressively isotropically stretched by the swelling while a second and third polymerization result in nearly unstretched and loosely crosslinked chains [1]] .…”

“…[1,5] To avoid this damage localization process leading to early fracture, it is possible to modify the network architecture to create additional energy dissipation mechanisms. Many strategies have been tried to increase the toughness of unfilled elastomers by network design.. [6] [7] [1,8] Our group has recently reported the successful design of multiple interpenetrating network elastomers through the sequential polymerization of acrylic monomers, in such a way that the network synthesized first becomes progressively isotropically stretched by the swelling while a second and third polymerization result in nearly unstretched and loosely crosslinked chains [1]] . When the elastomer is highly stretched or broken, the prestretched network chains break in the bulk of the elastomer well before the unstretched ones, significantly delaying the nucleation and propagation of a macroscopic crack.…”

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AbstractWe recently reported the general design and properties of new multiple network elastomers with an exceptional combination of stiffness, toughness and elasticity [1] .

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