Role of entropy in the thermodynamic evolution of the time scale of molecular dynamics near the glass transition

Abstract

In this Letter, 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 $\tau$ 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. As an example, we revise the Avramov entropic model of the dependence $\tau (T,\rho )$, 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 $S$.

References in corpus (21)

• "Isomorphs" in liquid state diagrams
• Pressure-energy correlations in liquids. IV. "Isomorphs" in liquid state diagrams
• Thermodynamical Scaling of the Glass Transition Dynamics
• Pressure-energy correlations in liquids. I. Results from computer simulations
• Thermodynamic interpretation of the scaling of the dynamics of supercooled liquids
• Pressure-energy correlations in liquids. II. Analysis and consequences
• Strong pressure-energy correlations in van der Waals liquids
• Thermodynamic scaling of diffusion in supercooled Lennard-Jones liquids
• Beyond power-law density scaling: Theory, Simulation, and Experiment
• Hidden scale invariance in molecular van der Waals liquids: A simulation study
• Density scaling as a property of strongly correlating viscous liquids
• Simplicity of condensed matter at its core: Generic definition of a Roskilde-simple system
• An equation for the description of volume and temperature dependences of the dynamics of supercooled liquids and polymer melts
• Thermodynamics of condensed matter with strong pressure-energy correlations
• Pressure-energy correlations and thermodynamic scaling in viscous Lennard-Jones liquids
• Generalizing Rosenfeld's excess-entropy scaling to predict long-time diffusivity in dense fluids of Brownian particles: From hard to ultrasoft interactions
• Estimating the density-scaling exponent of a monatomic liquid from its pair potential
• Scaling of Volumetric Data in Model Systems Based on the Lennard-Jones Potential
• Entropy Basis for the Thermodynamic Scaling of the Dynamics of OTP
• Activation Volume in the Density Scaling Regime: Equation of State and Its Test by Using Experimental and Simulation Data
• Dynamic heterogeneity of glass-forming liquids in the density scaling regime

Cited by in corpus (2)

• Studies of the Lennard-Jones fluid in 2, 3, and 4 dimensions highlight the need for a liquid-state 1/d expansion
• In search of invariants for viscous liquids in the density scaling regime: Investigations of dynamic and thermodynamic moduli