Abstract
Transport coefficients, such as viscosity or diffusion coefficient, show significant dependence on density or temperature near the glass transition. Although several theories have been proposed for explaining this dynamical slowdown, the origin remains to date elusive. We apply here an excess-entropy scaling strategy using molecular dynamics computer simulations and find a quasiuniversal, almost composition-independent, relation for binary mixtures, extending eight orders of magnitude in viscosity or diffusion coefficient. Metallic alloys are also well captured by this relation. The excess-entropy scaling predicts a quasiuniversal breakdown of the Stokes-Einstein relation between viscosity and diffusion coefficient in the supercooled regime. Additionally, we find evidence that quasiuniversality extends beyond binary mixtures, and that the origin is difficult to explain using existing arguments for single-component quasiuniversality.
Highlights
Transport coefficients, such as viscosity or diffusion coefficient, show significant dependence on density or temperature near the glass transition
We find a plateau in the intermediate scattering function (ISF) extending over almost five decades with a stretching exponent β = 0.55 at the lowest temperature, i.e., the ISF is well fitted by the stretched exponential function exp1⁄2Àðt=ταÞβ, where τα is the α-relaxation time
We find that the fractional SE exponent for our most supercooled 2:1 Kob–Andersen binary Lennard–Jones (KA) data is ξ ≈ 0.73, which interestingly is the number found in simulations of the one-dimensional East model in dynamical facilitation[64]
Summary
Transport coefficients, such as viscosity or diffusion coefficient, show significant dependence on density or temperature near the glass transition. We apply here an excess-entropy scaling strategy using molecular dynamics computer simulations and find a quasiuniversal, almost composition-independent, relation for binary mixtures, extending eight orders of magnitude in viscosity or diffusion coefficient. Several theories have been proposed to explain this phenomenon, for instance: random first-order transition theory, entropy-controlled theories, dynamical facilitation, bond-orientational order, free-volume theories, elastic models, and more[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15] Despite these intriguing theories, a broadlyaccepted and universal picture of what controls the change in transport coefficients near the glass transition has not yet manifested itself, even for the simplest supercooled liquids. A review of R-simple liquids and their isomorphs is given in ref. 55
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