Super stable surface nanobubbles under chemical stimuli

Abstract

Surface nanobubbles in chemical environments significantly influence various industrial processes. In the chemical industry, oxygen scavengers are frequently added to deaerators and boilers to remove dissolved oxygen, improving thermal efficiency and protecting equipment. We hypothesised that oxygen scavengers could cause surface nanobubbles to vanish by consuming dissolved oxygen in the surrounding liquids. This study investigates the morphological changes of surface air nanobubbles in a solution containing an oxygen scavenger (sodium sulphite) by atomic force microscopy. Contrary to our hypothesis, the experiment showed that surface nanobubbles did not eventually dissolve upon exposure to the oxygen scavenger; instead, they grew. To explore the gas sources that flew into surface bubbles, we estimated the saturation level of dissolved nitrogen by simulating microbubble shrinking in the oxygen scavenger solutions with the Epstein-Plesset model. The estimated saturation level of dissolved nitrogen is ∼ 1.12, suggesting oxygen depletion creates an oversaturation of dissolved nitrogen. These findings provide crucial insights into the fundamental understanding of nanobubble stability and offer potential strategies for controlling surface nanobubbles in practical applications.