Molecular dynamics simulations on self-healing behavior of photo-polymerization network

Recently, a variety of reversible chemical bonds are incorporated into thermoset polymers to design stimuli-responsive materials. Light-triggered dynamic network is advantageous since it is simple, inexpensive and easy controlled. In this paper, the dynamic photo-responsive network structure with labile bonds and free ethylene dimethacrylate (EGDMA) molecules was constructed. Under the stimulus of UV light, the labile bonds homolytically cleaved and the network was separated into small sections. Then the EGDMA monomers linked these small sections together to form a new network with higher crosslink density. Such depolymerization and polymerization processes would result in the self-healing of materials. Therefore, molecular dynamics method was applied to simulate the interface self-healing process of this polyurethane material under light stimulation condition. The mechanical properties of the healed networks under uniaxial tension were examined. The results showed that self-healing occurs at the interface of materials due to the polymerization, and the mechanical properties of the healed materials are strengthened when compared to that of the fresh samples. Moreover, the effect of crosslinking agent on the self-healing was investigated. The best mechanical properties of healed sample are obtained when the crosslinking agent reacts exactly with the polyurethane network.