Particle-Filled Emulsion Drops Show Flow-Induced Partial Coalescence, but Only Transiently

Area of Science:

• Fluid Dynamics
• Materials Science
• Colloid Science

Background:

• Partial coalescence is a droplet merging process where droplets do not regain a spherical shape.
• Emulsions with high particle loading exhibit solid-like behavior, influencing droplet dynamics.

Purpose of the Study:

• To investigate shear flow-induced partial coalescence in particle-filled emulsions.
• To understand the role of internal particles in droplet shape evolution during coalescence.

Main Methods:

• Flow-visualization study of poly-(ethylene oxide) drops in polyisobutylene, filled with silica particles (>50 vol%).
• Application of varying shear rates to induce and observe partial coalescence and shape recovery.
• Analysis of droplet shape dynamics under different shear conditions and particle loadings.

Main Results:

• Particle-filled drops initially adopt nonspherical shapes and undergo partial coalescence into highly irregular forms under shear.
• The rate of reversion to a spherical shape increases with higher shear rates and drop loading.
• Drops can maintain irregular shapes for extended periods at low shear rates or low particle concentrations.

Conclusions:

• Partial coalescence in these emulsions is attributed to particle-induced solid-like behavior.
• The gradual reversion to sphericity is driven by viscous stress and particle rearrangements during collisions, rather than capillarity.
• The findings offer insights into the complex rheology and deformation of concentrated particle-laden emulsions.