Ion Adsorption at Surface Nanobubble Interface and Its Influence on Gas Transport

Abstract

Surface nanobubbles are nanoscopic gaseous domains that reside at solid–liquid interfaces and exhibit anomalous stability against diffusive dissolution. Despite similarities in size and composition to bulk nanobubbles, the physicochemical mechanisms governing their interfacial persistence remain incompletely understood. Here, molecular dynamics simulations employing the polarizable SWM4-NDP water model were used to investigate the effects of LiCl on the interfacial structure and transport properties of surface nanobubbles. Both Cl– and Li+ ions access the interfacial region; however, their behaviors differ markedly. Cl– ions exhibit subsurface enrichment and remain localized near the interface for extended periods, whereas Li+ ions largely retain their hydration shells and display only transient interfacial encounters. Residence time analysis confirms substantially longer interfacial lifetimes for Cl– than for Li+. Despite this ion specific interfacial affinity, electrolyte accumulation produces negligible changes in nitrogen gas transport across the interface. The potential of mean force for N2 permeation and the orientational ordering of interfacial water molecules remain essentially unchanged in the presence of ions. These findings demonstrate that although both ions access the interfacial region, only anions exhibit sustained interfacial affinity, yet this enrichment does not measurably influence gas transfer kinetics, pointing instead toward alternative mechanisms governing nanobubble stability.