The phenomenon of bubble entrapment during capsule formation

Area of Science:

• Materials Science
• Fluid Dynamics
• Chemical Engineering

Background:

• Polymer capsules are synthesized via drop impact, a process sensitive to bubble entrapment.
• Entrapped air bubbles can compromise the structural integrity and quality of the resulting polymer capsules.

Purpose of the Study:

• To experimentally investigate the mechanism of air bubble entrapment during polymer capsule formation.
• To identify the key physical parameters governing bubble entrapment in this process.

Main Methods:

• Utilized high-speed imaging to capture the dynamics of viscous poly-anion drops impacting a poly-cation solution.
• Analyzed the impact crater morphology and bubble pinch-off dynamics across a range of impact Weber numbers.

Main Results:

• Bubble entrapment occurs due to the collapse of the impact crater over the submerged drop.
• The bubble pinch-off process is characterized as the thinning of a gas filament driven by fluid flow.
• Low Weber numbers (We) indicate a combined influence of surface tension and inertia, while high We regimes are inertia-dominated.

Conclusions:

• The transition in governing forces (surface tension vs. inertia) correlates with the critical cone angle observed in simpler drop impacts.
• Understanding bubble entrapment dynamics is crucial for controlling polymer capsule membrane quality.