Pair entropy and universal viscosity scaling for molecular systems via molecular dynamics simulations

Abstract

The scaling between the excess entropy and transport coefficients of liquids is an interesting property found by Rosenfeld in atomistic simulations. Later, Dzugutov proposed to estimate the excess entropy on the basis of the pair entropy. That approach has been shown to work well for atomic liquids and rigid molecules, but there is a problem of pair entropy definition for molecular substances in general. In this work, we propose a new method of estimation of the pair contribution to the excess entropy for hydrocarbon liquids. We present the results on viscosity-pair entropy Rosenfeld scaling for linear alkanes and an aromatic compound in two different force fields, and compare the results with the available experimental and correlation data. We show that our method accounts for 75–90% of excess entropy changes in molecular liquid, comparable to the pair entropy contribution in atomic liquids. The universal nearly-univariate dependence of the scaled viscosity and pair entropy is observed for each compound at different temperatures, and the scaling is shown to be transferable between the force fields models.