Pinch-off of bubbles in a polymer solution

Abstract

The formation of gas bubbles in a liquid occurs in various engineering processes, such as during foam generation or agitation and mixing in bubbly flows. A challenge in describing the initial formation of a gas bubble is due to the singular behavior at pinch-off. Past experiments in Newtonian fluids have shown that the minimum neck radius follows a power-law evolution shortly before the break-up. The exponent of the power-law depends on the viscosity of the surrounding Newtonian liquid, and ranges from 0.5 for low viscosity to 1 for large viscosity. However, bubble formation in a viscoelastic polymer solution remains unclear, and in particular, if the evolution is still captured by a power-law and how the exponent varies with the polymer concentration. In this study, we use high-speed imaging to analyze the bubble pinch-off in solutions of polymers. We characterize the time evolution of the neck radius when varying the polymer concentration and thus the characteristic relaxation time of the polymer chains, and describe the influence of viscoelasticity on the bubble pinch-off. Our results reveal that the presence of polymers does not influence the thinning until the latter stages, when their presence in sufficient concentration delays the pinch-off.