Intrinsic atomic-level forces in polymer networks exhibiting non-gaussian effects: relationship with the limited chain extensibility

Abstract.

Intrinsic atomic-level forces for networks exhibiting non-Gaussian effects were evaluated during the integration of the equations of motion using the Verlet algorithm. The forces acting on the junction points of the cross-linking chains and the elastomeric chains of unimodal and bimodal network arrangements showed no apparent change as a consequence of the network variation. The forces acting on the short chains in a bimodal network cross-linked using sulfur atoms and relatively long polyquinone chains had much higher values than those in a unimodal network arrangement. Nevertheless, the intrinsic forces acting on the polyquinone atoms decreased dramatically as a result of the formation of bimodal networks. The presence of relatively long polyquinone chains in bimodal networks caused the short sulfur chains to stretch to their maximum extensibility and they can no longer increase their end-to-end separation by simple rotations about their skeletal bonds. Limited chain extensibility of the short chains resulting from the deformation of the bond angles and bond lengths led to much higher potential energies, as determined using the dynamic quenching technique. This resulted in the non-Gaussian effects known for bimodal networks and their subsequent anomalous mechanical properties. The dynamical behavior of the nuclei bending and torsional angles was also investigated for the unimodal and bimodal networks.