Tuning structure and mobility of solvation shells surrounding tracer additives

Area of Science:

• Physical Chemistry
• Soft Matter Physics
• Computational Fluid Dynamics

Background:

• Understanding solvent dynamics around tracer particles is crucial for predicting fluid behavior.
• Tracer-solvent interactions significantly influence local solvation structure and particle mobility.
• Previous work suggests specific interactions can enhance tracer diffusion by altering solvation shells.

Purpose of the Study:

• To investigate how modifying tracer-solvent interactions affects position-dependent solvent mobility.
• To compare the effects of hard-sphere versus soft repulsive interactions on solvent dynamics.
• To elucidate the mechanisms behind enhanced tracer diffusivity and its concentration dependence.

Main Methods:

• Molecular dynamics (MD) simulations were employed to model particle interactions and dynamics.
• A stochastic Fokker-Planck equation based approach was used to analyze solvent mobility.
• Two distinct tracer-solvent interaction potentials were compared: hard-sphere and soft repulsion.

Main Results:

• A soft repulsive interaction, designed to suppress coordination shells, enhanced both tracer and solvent mobility at infinite dilution.
• This suppression of local solvation structure rationalizes the increased diffusivity of the tracer.
• At higher tracer concentrations, where surfaces are closer, these same interactions suppressed position-dependent solvent dynamics.

Conclusions:

• Tracer-solvent interaction design can controllably alter local solvent mobility.
• The impact of suppressed solvation structure on solvent dynamics is concentration-dependent.
• Understanding these effects is key for designing materials with tailored transport properties.