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  • Title: Fractional Coupling of Primary and Johari-Goldstein Relaxations in a Model Polymer.
    Author: Massa CA, Puosi F, Leporini D.
    Journal: Polymers (Basel); 2022 Dec 19; 14(24):. PubMed ID: 36559927.
    Abstract:
    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.
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