Interactions Governing the Dispersion of Silver Nanoparticles in Ionic Liquids: A Combined All-Atom and Coarse-Grained Molecular Dynamics Study.

Stabilization of nanoparticle (NP) dispersions in ionic liquids (ILs) is essential for a range of applications including catalysis, solar power harvesting, and novel technologies like liquid mirrors for space telescopes. Stabilizing these dispersions is particularly challenging as the agglomerated state is thermodynamically more stable than the dispersed state, resulting in a natural tendency to aggregate. However, kinetic stabilization can be achieved by fine-tuning the molecular interactions within the IL and at the IL-NP interface. In this study, using all-atom and coarse-grained molecular dynamics simulations, we explore these interactions for 1-ethyl-3-methylimidazolium ethyl sulfate ([EMIM][ESO₄]) IL with silver (Ag) NPs. We show that the imidazolium ring of the cation and the sulfur headgroup of the anion adsorb preferentially on the NP surface forming solvation layers. In particular, the [EMIM] cation closer to the NPs is oriented parallel to the surface, while the [ESO₄] ions are oriented perpendicular, with the cation adsorbing slightly stronger than the anion. Additionally, we found that smaller NPs with a higher surface area-to-volume ratio slow down the translational motion of the ions. The predicted potential of mean force for aggregation explicitly highlighted the existence of the potential barrier. For example, the kinetic barrier of ∼ 60 kJ/mol was observed preventing the aggregation of 1.5 nm diameter AgNPs. These findings highlight dispersion characteristics, such as the interaction strength and the particle size, as tunable parameters for introducing kinetic barriers to agglomeration and stabilizing the dispersion. Such studies are crucial for tailoring ILs to specific applications, enabling precise exploration of their vast design space.