Secondary Johari–Goldstein relaxation in linear polymer melts represented by a simple bead-necklace model

Molecular dynamics simulations of linear polymer melts represented using simple bead-necklace models showed for the first time a distinct separation between primary α- and secondary Johari–Goldstein β-processes. The split is observed only for models where the bead diameter is much larger than the bond length connecting the beads. The overlap of neighboring (along the chain) beads results in a mismatch between local intramolecular correlations and intermolecular packing (cage size), which leads to two processes in segmental relaxation characterized by torsional autocorrelation function. The observed β-process shows all characteristics and correlations expected for the true Johari–Goldstein process.