Investigation of the Affine Model for the Network Chains by Molecular Dynamics Simulation

ABSTRACT Molecular dynamics simulations were conducted to investigate the relationship between microstructural changes and macroscopic deformations in rubber materials. Coarse‐grained (CG) models of isoprene rubber (IR) with varying crosslink densities (CD) were constructed, and uniaxial tensile stretching was simulated. The positions of effective crosslink points, together with the magnitudes and orientations of the end‐to‐end vectors of selected chains under stretching, were analyzed and compared with their affine counterparts. The results reveal significant deviations between the simulations and the predictions of the affine model. These deviations depend on orientation: along the stretching direction, they are larger than those in the lateral directions for the positions of crosslinkers and the end‐to‐end distances, though not for the chain orientations. In general, the deviations—except for the orientation of the end‐to‐end vectors—decrease with increasing crosslink density and increase with stretching. Moreover, the deviation of an individual chain calculated in an instantaneous state differs significantly from that averaged over many equilibrium states, whereas the deviations averaged over the entire system are weakly affected by the averaging over states. Overall, the findings demonstrate that the deformation of individual chains in a network does not strictly conform to the affine model, either in magnitude or in orientation, providing important insights for constitutive modeling and mechanical property analysis.