Density scaling of the diffusion coefficient at various pressures in viscous liquids

TL;DR

This paper develops an analytical model based on thermodynamics and solid-state defect theory to describe how the diffusion coefficient in viscous liquids scales with density across various pressures, aligning with recent simulation results.

Contribution

It introduces a second-order polynomial function for density scaling of diffusion coefficients, directly linking parameters to the Gruneisen constant, and confirms the model with simulation data.

Findings

Density scaling diffusion isotherms collapse onto a master curve.

The model parameters are determined solely by the scaling exponent.

Results agree with recent computer simulations of Lennard-Jones liquids.

Abstract

Fundamental thermodynamics and an earlier elastic solid-state point defect model [P. Varotsos and K. Alexopoulos, Phys. Rev B 15, 4111 (1977); 18, 2683 (1978)] are employed to formulate an analytical second-order polynomial function describing the density scaling of the diffusion coefficient in viscous liquids. The function parameters are merely determined by the scaling exponent, which is directly connected with the Gruneisen constant. Density scaling diffusion coefficient isotherms obtained at different pressures collapse on a unique master curve, in agreement with recent computer simulation results of Lennard-Jones viscous liquids, [D. Coslovich and C.M. Roland, J. Phys. Chem. B 112, 1329 (2008)].