Water-Mediated Stability of Ionic Liquids Confined in Aqueous Droplets: Molecular Dynamics Insights with Atmospheric Parallels

TL;DR

This study uses simulations to explore how ionic liquids stabilize water bubbles, with implications for atmospheric processes like cloud formation.

Contribution

The study reveals water-mediated stabilization mechanisms in ionic liquid–water systems with parallels to atmospheric phenomena.

Findings

Protic ILs stabilize water bubbles more effectively than aprotic ILs due to hydrogen bonding.

Ionic insertion at bubble interfaces increases volume by up to 36% at high concentrations.

Molecular descriptors like HB lifetimes and energy trends offer insights for environmental models.

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 (E
C/E
LJ) trends, density symmetry)
provide transferable parameters for more realistic representations
of water uptake and activation in environmental models.

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