A theoretical multiscale approach for topology-based toughness design of network polymers

초록

Network-structured polymers enable high rigidity but suffer from premature fracture due to strain localization at densely crosslinked sites. This work establishes a multiscale framework to quantify toughness enhancement achieved through topological modification of epoxy thermosets using homogeneous and flexible toughening agent. Thermoset microstructures modeled using all-atom molecular dynamics simulations exhibited componentdependent asymmetric damage under tensile loading: hardener segments underwent early intramolecular distortion and scission, whereas the flexible toughener retained extensibility and delayed the covalent-bond rupture. Such component-specific behavior promotes more homogeneous pore nucleation within the network, preserving load-transfer pathways at large strains. Accordingly, epoxy networks with appropriately designed topologies exhibited fracture energies up to 20 times greater than neat epoxy while retaining network homogeneity. Such molecular-level properties were coupled to a finite element model to characterize the influence of continuum-level stress concentrations and crack initiation. It was found that the dissipation of externally applied strain energy is primarily determined by crack-tip blunting and substantial expansion of the plastic zone, thus identifying topological modulation of the microstructure as a key factor in enhancing toughness. The proposed theorical multiscale framework provides a mechanistic link from chain-level rearrangements to macroscopic crack resistance and offers quantitative design guidance for next-generation thermoset polymers that balance stiffness with effective toughness.

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