Tuning structure and mobility of solvation shells surrounding tracer additives

TL;DR

This study uses molecular dynamics and theoretical modeling to explore how modifying tracer-solvent interactions influences local solvent mobility and structure, revealing effects at different tracer concentrations.

Contribution

It demonstrates how tailored tracer-solvent interactions can enhance or suppress solvent mobility depending on tracer proximity and concentration.

Findings

Soft repulsive interactions increase solvent mobility at infinite dilution.

Proximity of multiple tracers can suppress solvent dynamics despite similar interactions.

Modified interactions can either enhance or hinder local solvation structure.

Abstract

Molecular dynamics simulations and a stochastic Fokker-Planck equation based approach are used to illuminate how position-dependent solvent mobility near one or more tracer particle(s) is affected when tracer-solvent interactions are rationally modified to affect corresponding solvation structure. For tracers in a dense hard-sphere fluid, we compare two types of tracer-solvent interactions: (1) a hard-sphere-like interaction; and (2) a soft repulsion extending beyond the hard core designed via statistical mechanical theory to enhance tracer mobility at infinite dilution by suppressing coordination-shell structure (Carmer et al., Soft Matter 8 (2011)). For the latter case, we show that the mobility of surrounding solvent particles is also increased by addition of the soft repulsive interaction, which helps to rationalize the mechanism underlying the tracer's enhanced diffusivity. However, if multiple tracer surfaces are in closer proximity (as at higher tracer concentrations), similar interactions that disrupt local solvation structure instead suppress the position-dependent solvent dynamics.