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Authors Grzybowska, K. ; Grzybowski, A. ; Pawlus, S. ; Pionteck, J. ; Paluch, M.
Title Role of entropy in the thermodynamic evolution of the time scale of molecular dynamics near the glass transition
Date 15.06.2015
Number 44857
Abstract In this paper, we investigate how changes in the system entropy influence the characteristic time scale of the system molecular dynamics near the glass transition. Independently of any model of thermodynamic evolution of the time scale, against some previous suppositions, we show that the system entropy S is not sufficient to govern the time scale defined by structural relaxation time tau. In the density scaling regime, we argue that the decoupling between tau and S is a consequence of different values of the scaling exponents gamma and gamma(S) in the density scaling laws, tau = f (rho(gamma)/T) and S = h(rho(gamma S) / T), where rho and T denote density and temperature, respectively. It implies that the proper relation between t and S requires supplementing with a density factor, u(rho), i.e., tau = g(u(.rho w(S)). This meaningful finding additionally demonstrates that the density scaling idea can be successfully used to separate physically relevant contributions to the time scale of molecular dynamics near the glass transition. The relation reported by us between tau and S constitutes a general pattern based on nonconfigurational quantities for describing the thermodynamic evolution of the characteristic time scale of molecular dynamics near the glass transition in the density scaling regime, which is a promising alternative to the approaches based as the Adam-Gibbs model on the configurational entropy that is difficult to evaluate in the entire thermodynamic space. As an example, we revise the Avramov entropic model of the dependence t (T,rho), giving evidence that its entropic basis has to be extended by the density dependence of the maximal energy barrier for structural relaxation. We also discuss the excess entropy S-ex, the density scaling of which is found to mimic the density scaling of the total system entropy S.
Publisher Physical Review / E
Wikidata
Citation Physical Review / E 91 (2015) Article No. 062305
DOI https://doi.org/10.1103/PhysRevE.91.062305
Tags structural relaxation polyvinyl acetate) hydrostatic-pressure supercooled liquids forming liquids temperature volume model dependence viscosity

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