Fractional Coupling of Primary and Johari-Goldstein Relaxations in a Model Polymer

• Published in: Polymers Vol. 14; no. 24; p. 5560
• Main Authors: Massa, Carlo Andrea, Puosi, Francesco, Leporini, Dino
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 19.12.2022; MDPI
• Subjects: Analysis; Correlation; dynamic heterogeneity; Heterogeneity; Johari-Goldstein relaxation; Laws, regulations and rules; Molecular dynamics; molecular-dynamics simulation; Polymer industry; polymer melt; Polymers; Power law; Simulation; polymer melt; molecular-dynamics simulation; dynamic heterogeneity; Johari-Goldstein relaxation
• ISSN: 2073-4360; 2073-4360
• DOI: 10.3390/polym14245560

A polymer model exhibiting heterogeneous Johari−Goldstein (JG) secondary relaxation is studied by extensive molecular-dynamics simulations of states with different temperature and pressure. Time−temperature−pressure superposition of the primary (segmental) relaxation is evidenced. The time scales of the primary and the JG relaxations are found to be highly correlated according to a power law. The finding agrees with key predictions of the Coupling Model (CM) accounting for the decay in a correlation function due to the relaxation and diffusion of interacting systems. Nonetheless, the exponent of the power law, even if it is found in the range predicted by CM (0<ξ<1), deviates from the expected one. It is suggested that the deviation could depend on the particular relaxation process involved in the correlation function and the heterogeneity of the JG process.