The Unusual Properties of Nanobubbles

Abstract

Nanobubbles are nanoscale bubble swarms with several peculiar properties that have been demonstrated to have a widespread application in the engineering and medical sectors. Surface nanobubbles are bubbles that are confned on a solid surface, whereas bulk nanobubbles are bubbles that are dispersed in the bulk liquid. Bulk nanobubbles have gained more attention in recent years owing to their long-term stability. Despite the several overwhelming applications, the fundamental research questions, for instance, driving force for nanobubble nucleation, interfacial properties in the presence of nanobubble, bubble dynamics under ultrasound and oscillating pressure feld, diferentiating nanobubbles and nanoparticles, etc. are still unanswered The present work aims to fll the gap in the literature and thus delineates to understand the nanobubble nucleation during salting-out efect, nanobubble dynamics under oscillating pressure felds, the efect of nanobubbles on Ray-Jones efect, etc. Based on the refractive index calculation, the excess dissolved gas does defnitely nucleate in the form of nanobubbles during the salting-out process. As a result, we intend to present evidence of nanobubbles that were supported by the freezing and thawing process. Based on Mie theory calculations, a novel approach for estimating the refractive index of nanobubbles is presented. When the salt concentration increases, so does the diferential in solubility, and bubble number density exhibits a positive correlation with the salt concentration . The infuence of an oscillating pressure feld on nanobubble dynamics during salting-out efects has been extensively discussed. The refractive index calculation and the electrical conductivity confrmed the evidence for the gas-fled nanobubbles. The screening of the electric double layer decreases the surface potential of the nanobubbles depending on the valency of the salt. Therefore, the equilibrium size of nanobubbles was observed to be higher in the presence of salts. The mean diameter of nanobubbles exhibits the inverse dependence on the surface potential. Our experimental fndings agree well with the theoretical prediction based on the mechanical stability model. Altogether, this thesis presents a novel mechanical stability model for nanobubbles which has been constructed by considering the ion cloud pressure, and it is shown to be twice the electrostatic pressure. The present nanobubble stability model not only predicts the existence of stable nanobubbles but is also in line with the experimental results obtained in this work. We also aim to explore further the surface tension of the salt solution that exhibits minima in the low salt concentration regime, which is widely known as the Jones-Ray efect. The nanobubble may be one of the contributing factors to the Jones-Ray efects. The size of the nanobubbles in the low salt regime is smaller than that in the high salt concentration regime, and therefore, the activity of the nanobubbles is expected more in the low salt concentration regime. In a further study, the coupling efect of nanobubbles and nanoparticles determines the refractive index and behavior of the suspension, concluding the existence of bulk nanobubbles.