How elasticity affects bubble pinch-off

TL;DR

This study investigates how viscoelastic properties influence bubble pinch-off dynamics, revealing differences from drop pinch-off and highlighting the role of polymer concentration and stresses.

Contribution

It demonstrates that bubble pinch-off in dilute polymer solutions lacks a thread due to weaker polymer stress divergence, contrasting with drop pinch-off.

Findings

No bubble thread in dilute solutions; appears only at high polymer concentrations.

Polymer stresses are singular but diverge weaker during bubble pinch-off.

Pinch-off dynamics are sensitive to needle size at high polymer concentrations.

Abstract

The pinch-off of bubbles in viscoelastic liquids is a fundamental process that has received little attention compared to viscoelastic drop pinch-off. While these processes exhibit qualitative similarities, the dynamics of the pinch-off process are significantly different. When a drop of a dilute polymer solution pinches off, a thread is known to develop that prevents breakup due the diverging polymer stresses. Conversely, our experiments reveal that this thread is absent for bubble pinch-off in dilute polymer solutions. We show that a thread becomes apparent only for high polymer concentrations, where the pinch-off dynamics become very sensitive to the size of the needle from which the bubble detaches. The experiments are complemented by numerical simulations and analytical modeling using the Oldroyd-B model, which capture the dilute regime. The model shows that polymer stresses are still singular during bubble pinch-off, but the divergence is much weaker as compared to drop pinch-off. This explains why, in contrast to droplets, viscoelastic bubble-threads do not appear for dilute suspensions but require large polymer concentrations