Molecular Dynamics Study of Ions at Surface Nanobubble Interface: Adsorption Without Gas Retention

Surface nanobubbles are nanoscale gaseous domains anchored at solid–liquid interfaces, notable for their unexpected stability against dissolution. Although they share size and composition with bulk nanobubbles, the mechanisms underlying their persistence at interfaces appear distinct. In this study, we employ molecular dynamics simulations with the polarizable SWM4-NDP water model to examine the role of ions at the nanobubble interface. Our simulations reveal a preferential enrichment of Cl− ions at the interface, while Li+ ions remain fully hydrated and largely excluded. Residence time analysis confirms this asymmetry, showing prolonged interfacial retention for Cl− relative to Li+. Interestingly, the transport of gas molecules across the interface remains largely unaffected by local ion density, and the potential of mean force profiles for nitrogen permeation as well as the orientational structure of interfacial water are nearly unchanged in the presence of ions. Together, these results indicate that while anions can accumulate at the nanobubble interface, their presence does not significantly influence gas transfer processes. This points toward stabilization pathways that extend beyond purely electrostatic effects, highlighting the importance of alternative mechanisms in sustaining surface nanobubbles.