Enhanced mixing of binary droplets induced by capillary pressure

Area of Science:

• Fluid Dynamics
• Microfluidics
• Interfacial Science

Background:

• Droplet mixing is critical for microfluidic applications.
• Understanding internal mixing mechanisms in coalescing droplets is essential.

Purpose of the Study:

• To investigate the internal mixing mechanisms of two free droplets in an immiscible phase.
• To study the effects of varying interfacial tension differences and droplet sizes on droplet mixing.

Main Methods:

• Development of a novel experimental setup for studying droplet coalescence.
• Observation and analysis of jet flow and liquid bridge expansion during coalescence.
• Proposal of a Reynolds number to characterize vortex size and mixing degree.

Main Results:

• Interfacial energy drives jet flow and liquid bridge expansion.
• Increased interfacial tension difference enhances mixing by intensifying jet flow and slowing bridge expansion.
• Decreased droplet size initially increases jet velocity but weakens mixing due to rapid bridge expansion.

Conclusions:

• Interfacial tension and droplet size are key parameters controlling internal mixing in coalescing droplets.
• A proposed Reynolds number effectively characterizes mixing intensity.
• The study provides an effective approach for enhancing droplet mixing in microfluidic systems.