Droplet Size Distribution in Emulsions.

Area of Science:

• Colloid and Surface Science
• Fluid Dynamics
• Materials Science

Background:

• Droplet size in emulsions significantly impacts rheological properties and application performance.
• The mechanisms controlling droplet size during emulsification are not fully understood.
• Current emulsification methods often lack detailed mechanistic understanding.

Purpose of the Study:

• To investigate the average droplet size and size distribution during high-shear emulsification.
• To compare high-shear emulsification with theoretical models of turbulent emulsification.
• To determine the key dimensionless numbers governing droplet size in high-shear mixing.

Main Methods:

• Utilized a high-shear mixer to create model oil-in-water emulsions.
• Emulsions were stabilized using a surfactant.
• Analyzed droplet size distribution and mean droplet size.

Main Results:

• Droplet size distribution followed a log-normal pattern, attributed to repetitive random drop breakup.
• High-shear emulsification results differ from turbulent emulsification predictions (e.g., Kolmogorov-Hinze theory).
• Mean droplet size scaled with the capillary number, not the Reynolds number, indicating continuous phase viscosity is critical.

Conclusions:

• High-shear emulsification mechanisms are distinct from turbulent flow models.
• The capillary number is a more relevant scaling parameter than the Reynolds number for high-shear emulsification.
• Understanding these mechanisms is crucial for controlling emulsion properties in various applications.