Role of entanglements and bond scission in high strain-rate deformation of polymer gels

A key factor that limits the practical implementation of polymer gels is low gel toughness. Here, we present coarse-grained molecular dynamics simulations of the effects of solvent molecular weight on the toughness of entangled and non-entangled polymer gels in the ballistic impact regime. Our results demonstrate that higher molecular weight solvents enhance gel toughness, and that mechanical properties including strength and toughness can be influenced by bond scission. Further, we find a remarkable two-step gel fracture mechanism on the molecular level: network chains undergo scission first (and well before fracture), followed by scission of solvent chains. For strain rates greater than inverse relaxation time of the solvent, long, highly entangled solvent chains provide fracture resistance even after the network chains break by effectively increasing the number of chains that must be broken as a crack propagates.