Fracture of model end-linked networks

Abstract

Advances in polymer chemistry over the last decade have enabled the synthesis of molecularly precise polymer networks that exhibit homogeneous structure. These precise polymer gels create the opportunity to establish true multiscale, molecular to macroscopic, relationships that define their elastic and failure properties. In this work, a theory of network fracture that accounts for loop defects is developed by drawing on recent advances in network elasticity. This loop-modified Lake–Thomas theory is tested against both molecular dynamics (MD) simulations and experimental fracture measurements on model gels, and good agreement between theory, which does not use an enhancement factor, and measurement is observed. Insight into the local and global contributions to energy dissipated during network failure and their relation to the bond dissociation energy is also provided. These findings enable a priori estimates of fracture energy in swollen gels where chain scission becomes an important failure mechanism.

Linking cavitation and fracture to molecular scale structural damage of model networks

“…This is the same synthetic approach employed recently to demonstrate a strong connection between molecular structure and both E and G c . 16 reported in the ESI. † The experimental notch test data presented in this work is taken from a previous publication.…”

“…[25][26][27] The structure of these gels, including the fraction of loop defects, has been characterized and reported separately. 16,20,[28][29][30][31] Since the network structure of these endlinked gels is well-defined, N can be calculated from the input length of the PEG chains 16,31 and not inferred from measurements of E as is typically done for networks that have ill-defined structure. 26,32,33 3 Tuning the elastofracture length Probing the cavitation to fracture transition in NIC requires the ability to rationally tune G c /E relative to the needle radius R. This presents a particular challenge as G c and E are materials properties that lack a deterministic link at the continuum level.…”

“…where U is the energy released per monomer segment. 16,34 Combining these two models and assuming that f = f o (ESI †) gives,…”

Bond strength regime dictates stress relaxation behavior

“…Given this, it is possible to design reconfigurable networks with the same stress relaxation times, but various moduli and presumably other properties such as gel fracture energy. 48 These findings inform reconfigurable network design by elucidating the relation between molecular parameters and material properties.…”

Cone cracks in tissue-mimicking hydrogels during hypodermic needle insertion: the role of water content

“…It is difficult to separate the elastic energy released upon fracture. 47 Neglecting the friction, the strain energy is G c À G th and this can be seen reducing with increasing water content. As the cone cracks keep growing the stress beneath the indenter keeps increasing.…”