Cofinement, entropy, and single-particle dynamics of equilibrium hard-sphere mixtures

TL;DR

This study investigates how confinement affects the relationship between entropy and particle dynamics in binary hard-sphere mixtures, revealing that certain entropy-based predictions remain valid under confinement, aiding understanding of confined fluid behavior.

Contribution

Introduces an efficient method to calculate partial molar excess entropies from transition-matrix Monte Carlo data and demonstrates the preservation of entropy-diffusivity relationships under confinement.

Findings

Self-diffusivities in confined fluids resemble bulk behavior at intermediate packing fractions.

Relationships between self-diffusivity and excess entropy are maintained under confinement.

Partial molar excess entropy can predict dynamical behaviors in confined fluids.

Abstract

We use discontinuous molecular dynamics and grand-canonical transition-matrix Monte Carlo simulations to explore how confinement between parallel hard walls modifies the relationships between packing fraction, self-diffusivity, partial molar excess entropy, and total excess entropy for binary hard-sphere mixtures. To accomplish this, we introduce an efficient algorithm to calculate partial molar excess entropies from the transition-matrix Monte Carlo simulation data. We find that the species-dependent self-diffusivities of confined fluids are very similar to those of the bulk mixture if compared at the same, appropriately defined, packing fraction up to intermediate values, but then deviate negatively from the bulk behavior at higher packing fractions. On the other hand, the relationships between self-diffusivity and partial molar excess entropy (or total excess entropy) observed in the bulk fluid are preserved under confinement even at relatively high packing fractions and for different mixture compositions. This suggests that the partial molar excess entropy, calculable from classical density functional theories of inhomogeneous fluids, can be used to predict some of the nontrivial dynamical behaviors of fluid mixtures in confined environments.