Modeling dynamically heterogeneous coupled relaxations

Abstract

A model describing dynamically heterogeneous relaxation in complex coupled systems is presented. The model predicts the splitting of a high-temperature single Debye relaxation to a low-temperature bimodal relaxation. The bimodal process shows a crossover from a Debye-type relaxation to an approximately stretched-exponential relaxation. Some general features of relaxation in complex systems emerge from the predictions of the model, and a comparison of the model with experiments is reported.

Heterogeneous coupled dissipation modeling of volume and enthalpy recovery in glass systems

“…This means that the effective relaxation time, , increases with time [30]. According to the present model, the relaxation of a SLC is carried out through the cooperative-dissipation, i.e.…”

“…Thus, the energy in a region can be transferred to others where it is dissipated, and this process is called as cooperative-dissipation [29,30]; 3. A glass system is formed by SLCs and LLCs [16,17,20].…”

“…In the HCD model, it was considered that the deviated energy of the SLCs dissipated by the self-dissipation is small enough and can be omitted compared with that by the cooperative-dissipation, i.e. 2 [29,30].…”

“…A thorough description of the HCD model has been given elsewhere [29,30], so here only the most important aspects of the model will be presented. Based upon the continuous approximation, the energy of a glass system, ( , ) U T t , which is equal to the sum of kinetic and potential energies, can be written as …”

“…Recently we have proposed a heterogeneous coupled dissipation scenario of glass transition, abbreviated for the sake of convenience as HCD, that describes in a unified way the relaxation dynamics, the glass transition and physical aging of supercooled liquids [29,30]. The key point of this model is the coupled dissipation between the SLCs and the LLCs and, moreover, the parameters that condition the response of materials to perturbation fields are considered non-distributed quantities.…”