Particle-stabilized emulsions comprised of solid droplets.

Area of Science:

• Colloid and surface science
• Materials science
• Rheology

Background:

• Oil-in-water emulsions are crucial in various industries.
• Traditional stabilization using surfactants can lead to instability.
• Particulate stabilization offers an alternative approach for emulsion stability.

Purpose of the Study:

• To investigate the kinetic stabilization of oil-in-water emulsions using silica particles.
• To compare the stability of particulate-stabilized emulsions with surfactant-stabilized ones.
• To explore the behavior of these emulsions under shear stress, focusing on gelation dynamics.

Main Methods:

• Preparation of oil-in-water emulsions with paraffin crystals and colloidal silica.
• Assessment of quiescent stability over extended periods.
• Application of shear stress to probe stability under flow conditions.
• Determination of critical droplet mass fraction (phi*) for gelation transition.

Main Results:

• Silica-adsorbed emulsions demonstrated long-term quiescent stability (months), surpassing surfactant-only systems (hours).
• Shear stress induced partial coalescence and gelation in the emulsions.
• A critical droplet mass fraction (phi*) was identified, sharply dividing slow and rapid gelation.
• Gelation time transitioned from hours (phi < phi*) to near-instantaneous (phi > phi*).

Conclusions:

• Colloidal silica provides effective kinetic stabilization for oil-in-water emulsions, outperforming surfactants.
• Emulsion gelation under shear is a critical phenomenon dependent on droplet concentration.
• The identified critical droplet mass fraction offers a key parameter for controlling emulsion rheology and stability under flow.