Examining the Effects of Solvent Quality on Material Fracture in Double Network Hydrogels

Double network (DN) hydrogels consist of two interpenetrating polymer networks: a highly cross-linked, brittle first network and a loosely cross-linked, ductile second network. Owing to this architecture, DN hydrogels exhibit exceptional mechanical properties and have been used in a vast range of applications such as tissue engineering and soft robotics. Prior experimental works have shown that DN fracture can be modulated via solvent conditions; however, the underlying molecular determinants of crack propagation and fracture are poorly understood. In this talk, we will present our recent efforts in using coarse-grained molecular dynamics simulations to examine DN hydrogel fracture with varying solvent quality. Simulations show that increasing solvent quality results in increased fracture stress and bond breaking events in the first network. In good solvents, the first network chains are stretched and thus undergo greater bond scission, which leads to the formation of distinct banded structures upon fracture. We hypothesize that banded structures act as physical crosslinkers for the second network and thereby enhance fracture stress. Overall, our simulations demonstrate that solvent quality can serve as a desirable design variable for tuning DN hydrogel fracture mechanics.