Secondary Johari-Gold stein 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 alpha- and secondary Johari-Goldstein beta-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 beta-process shows all characteristics and correlations expected for the true Johari-Goldstein process. (C) 2010 Elsevier B.V. All rights reserved.