Ion adsorption stabilizes bulk nanobubbles

The mechanism leading to the extraordinary stability of bulk nanobubbles in aqueous solutions remains an outstanding problem in soft matter, modern surface science, and physical chemistry science. In this work, the stability of bulk nanobubbles in electrolyte solutions under different pH levels and ionic strengths is studied. Nanobubbles are generated via the technique of ultrasonic cavitation, and character-ized for size, number concentration and zeta potential under ambient conditions. Experimental results show that nanobubbles can survive in both acidic and basic solutions with pH values far away from the isoelectric point. We attribute the enhanced stability with increasing acidity or alkalinity of the aque-ous solutions to the effective accumulation of net charges, regardless of their sign. The kinetic stability of the nanobubbles in various aqueous solutions is evaluated within the classic DLVO framework. Further, by combining a modified Poisson-Boltzmann equation with a modified Langmuir adsorption model, we describe a simple model that captures the influence of ion species and bulk concentration and reproduce the dependence of the nanobubble's surface potential on pH. We also discuss the apparent contradiction between quantitative calculation by ion stabilization model and experimental results. This essentially requires insight into the structure and dynamics of interfacial water on the atomic-scale. (c) 2021 Elsevier Inc. All rights reserved.

Automated summary

This study investigates the stability of bulk nanobubbles in electrolyte solutions under different pH levels and ionic strengths, demonstrating their survival in acidic and basic solutions due to effective accumulation of net charges. The kinetic stability of nanobubbles in various aqueous solutions is evaluated within the classic DLVO framework, and a model capturing the influence of ion species and bulk concentration on the nanobubble's surface potential is described. Discussions on the contradiction between quantitative calculation and experimental results highlight the need for insights into the atomic-scale structure and dynamics of interfacial water.