Mapping coalescence of micron-sized drops and bubbles

Area of Science:

• Fluid dynamics
• Colloid science
• Interfacial phenomena

Background:

• Precise control of drop/bubble collision stability is vital for emulsion formulation, solvent extraction, and multiphase microfluidics.
• Existing models often lack detailed mapping of conditions influencing coalescence under combined colloidal and hydrodynamic forces.

Purpose of the Study:

• To numerically map the conditions governing micron-sized drop/bubble coalescence.
• To investigate the interplay of colloidal forces, Brownian motion, and low Reynolds number hydrodynamics on collision stability.
• To identify parameters that stabilize or destabilize collisions.

Main Methods:

• Utilized a validated numerical model to simulate drop/bubble collisions.
• Analyzed the influence of equilibrium surface forces and film thickness on collision outcomes.
• Investigated hydrodynamic effects, including interaction velocity and drop deformation.
• Determined conditions leading to instability upon separation due to negative hydrodynamic pressure.

Main Results:

• Accurate prediction of collision outcomes is possible when hydrodynamic effects are negligible by understanding equilibrium surface force variations.
• Hydrodynamic effects can stabilize collisions that are unstable at equilibrium.
• Negative hydrodynamic pressure can cause collisions to become unstable upon separation.
• Scaling analyses are insufficient for constant force collisions where timescales are comparable.

Conclusions:

• Detailed understanding of surface forces and hydrodynamics is key to predicting and controlling drop/bubble collision stability.
• The study provides a framework for optimizing processes reliant on precise control of interfacial phenomena.
• Initial conditions are critical for predicting collision outcomes in certain dynamic regimes.