Topological Structure and Mechanics of Glassy Polymer Networks

The influence of chain-level network architecture (i.e., topology) on the mechanics of polymer networks is explored with coarse-grained molecular simulations and graph-theoretic concepts. A modified Watts-Strogatz model is used to control the graph properties of the networks, and the corresponding physical properties are studied with simulations. The topology of dynamically-cured networks is compared with the modified Watts-Strogatz model, and found to agree surprisingly well: the dynamically-assembled topologies were intermediate between lattice and random topologies, due to the restriction of finite chain length. Further, the linear and nonlinear stress response, bond breaking, and non-affine displacements of glassy networks are analyzed as a function topological disorder. The architecture strongly affects the flow stress, onset of chain scission, and ultimate stress, while the modulus and yield point are unchanged. Internal restrictions imposed by topological disorder alter the chain-level dynamics in the flow regime, and the degree of coordinated chain failure at the ultimate stress. The properties are sensitive to even incremental changes to topology, so the overall network architecture, beyond simple defects, is predicted to be a meaningful physical parameter for mechanics.