Molecular Simulationof Effects of Network Structureon Fracture Behavior of Gels Synthesized by Radical Polymerization

The synthesis of high-strength gels with many entanglements by radical polymerization with high monomer and low cross-linker concentrations has recently been reported by several groups. In order to elucidate the toughening mechanism of such high-strength gels, the fracture behavior of gels synthesized by radical polymerization is studied by a coarse-grained molecular dynamics simulation. The simulation results qualitatively reproduce the reported experimental results; the gels formed with high monomer and low cross-linker concentrations have a small number of elastically effective chains due to cross-linking, but many polymer entanglements, and exhibit high toughness without sacrificing the shear modulus. In the tough gels, the structural changes that suppress the orientation of the polymer chains in the elongation direction and stress concentration are confirmed. Analysis of the relationship between network structure and fracture behavior reveals that the chain length between cross-linking points and the number of entanglements are important for the toughness of the gels.