Multi-scale analysis of the effect of surfactants on bubble properties

The effect of surfactants on bubble properties was examined in turbulent conditions. A multi-scale analysis was accomplished with the primary aim to identify the relationship between the size-scale determined surface properties leading to the decrease in bubble size. The adsorption of the surfactants triggers chain reactions acting along different size-scales: it diminishes the tension at the air-liquid interface and increases its surface elasticity (micro/nano-scale; 10⁻¹⁰ to 10⁻⁵ m) leading to modified coalescence and breakup properties and lower bubble rise velocity (meso-scale; 10⁻⁵ to 10⁻² m) that finally result a smaller bubble size (macro-scale; >10⁻² m). The weakly surface-active DF200 and Pentanol cause a different change in the dynamic properties of the air-liquid interface compared to the strongly surface-active DF250 and PPG leading to differences in size-scale properties and eventually in bubble size. The main result of this work is a comprehensive picture of the dynamics of surface-active molecules affecting bubble size in the presence of random momentum transfer.