Water-mediated stability of ionic liquids confined in aqueous droplets: molecular dynamics insights with atmospheric parallels

Abstract

This study investigates the structural and volumetric effects of protic ([cho][gly]) and aprotic ([emim][BF4]) ionic liquids (ILs) on confined aqueous bubbles via molecular dynamics simulations. Pure water bubbles exhibit near-spherical symmetry and slight volumetric expansion (∼4%) with increasing temperature, consistent with thermal expansion. The introduction of ILs induces significantly larger volume increases (up to 36% at high ion concentrations) due to ionic insertion at bubble interfaces, which reorganizes the hydrogen bond (HB) network and expands the structure. Protic ILs show stronger stabilizing effects than aprotic ILs, attributed to cooperative HB formation with water and among ions. Dynamic analyses reveal that ILs maintain or increase HB numbers and lifetimes while raising rupture energy barriers, reinforcing bubble cohesion and thermal resilience. Despite volumetric changes, bubble morphology and water density symmetry remain intact, highlighting ILs as active structural stabilizers. Beyond nanoconfined IL−water systems, these water-mediated stabilization mechanisms parallel atmospheric processes in which hygroscopic growth, cloud condensation nuclei (CCN) activation, and particle lifetimes are governed by interfacial organization. The molecular descriptors established here (HB lifetimes, rupture free-energy (ΔG), Coulombic/Lennard−Jones interaction energy (EC/ELJ) trends, density symmetry) provide transferable parameters for more realistic representations of water uptake and activation in environmental models.