Crosslink-to-Entanglement Transition in Polymer Networks and Gels

Mechanical properties of polymer networks and gels are manifestations of the synergistic effect of crosslinks and entanglements. To elucidate the effect of crosslinks and entanglements on the network and gels elasticity, we use coarse grained molecular dynamics simulations of polymer networks and gels prepared by crosslinking bead-spring chains in a melt state by varying the degree of polymerization between crosslinks. For such networks and gels, we identify a transition from crosslink- to entanglement-controlled elasticity with increasing the degree of polymerization of network strands between crosslinks and the equilibrium gel’s swelling ratio. We show how specific features of this transition are related with changes in entanglement and structural shear moduli characterizing two different modes of network deformation. This crosslink-to-entanglement transition results in saturation of the shear modulus at small deformations and renormalization of the degree of polymerization of the effective network strands determining nonlinear elastic response in the strongly entangled networks and gels. The simulation results are compared with experimental data on the network and gel elasticity.