The stability and geometrical characteristics of solid-liquid interfacial nanobubbles in complex aqueous solution environments

Abstract

Interface nanobubbles (INBs) have potential applications in various fields, and their existence has been adequately demonstrated. However, the stability and geometric morphology of INBs in complex solution environments remain less clear. In this study, we investigated the stability and geometrical characteristics of INBs exposed to various solution environments both in situ and statistically. We find that INBs in a 40 vol% ethanol-water solution exhibits a decrease in width but an increase in height and contact angle (from the gas side). In cationic, anionic, and nonionic surfactant solutions, the height of INBs tends to increase, accompanied by a reduction in width, resulting in an increase in the contact angle. The observed increase in height may be attributed to the expansion of INBs, which is likely caused by a reduction in surface tension. This suggests that the gas-liquid interface of INBs remains unsaturated by organic moieties in both pure water and solutions of low surfactant concentrations. The increase in contact angle when INBs are exposed to solutions with a lower liquid-gas interfacial tension is contrary to expectations, which may be caused by the increased solid-gas interfacial tension. However, in different concentrations of NaCl solution, the INBs remain stable with minimal changes in their geometrical parameters. Furthermore, the experimental results demonstrate that INBs exhibit strong stability under lateral shear force and strong vertical pressure. The findings of this study contribute to a deeper understanding of the INBs and provide theoretical support for applications related to INBs.