Stability of ultra-fine bubbles against temperature, phase change, and shear stress

Abstract

Most previous studies concerning applications of ultra-fine bubbles have focused on their use at room temperature, and thus there has been little research into their stability at high and low temperatures and during phase changes. Additionally, external forces such as shear are expected to have an effect during application, but very few studies have examined the effects of shear, mainly because particle size distributions have traditionally been measured under static conditions after the generation of ultra-fine bubbles. Therefore, in this study, we measured the particle size distribution of ultra-fine bubbles under more application-like conditions by subjecting a mixture of ultra-fine bubbles to shearing, temperature changes, boiling, freezing, and thawing. We found that stability was maintained at temperatures up to 50 °C, but stability was lost at 60 °C and during boiling. Relative stability was maintained with respect to freeze-thaw and shear. We conclude by comparing these results to a case involving ultrasound irradiation.