Using a Molecular Stopwatch to Study Particle Uptake in Pickering Emulsions

Area of Science:

• Colloid and Surface Science
• Materials Chemistry

Background:

• Emulsion droplets with composite interfaces offer tunable properties.
• Controlling interfacial structure is key for advanced materials design.

Purpose of the Study:

• To investigate the formation of emulsion droplets with composite interfaces using colloidal PMMA particles and a pH-switchable lipid film (tetradecylammonium hydrogen phosphate, TAHP).
• To explore how varying particle size and aqueous pH influence interfacial structure and droplet size.
• To demonstrate the potential for rational design of tunable emulsion systems.

Main Methods:

• Combining colloidal PMMA particles with TAHP to form emulsion droplets.
• Tuning interfacial structure and droplet size by varying particle size and aqueous pH (pH 5, 7, and 9).
• Analyzing the relationship between particle adsorption rate, film assembly rate, and resulting droplet characteristics.

Main Results:

• At pH 5, rapid TAHP assembly yielded small droplets with a mixed interfacial structure, independent of particle volume fraction.
• At pH 7, slower TAHP assembly showed a systematic correlation between particle size and droplet size.
• At pH 9, TAHP was inactive, resulting in standard Pickering emulsions.
• At pH 5, interfacial particle density and droplet size were readily tunable.

Conclusions:

• The study demonstrates a method for creating emulsion droplets with tunable composite interfaces by controlling particle-adsorption and lipid-film assembly kinetics.
• Varying pH and particle size offers precise control over interfacial structure and droplet characteristics.
• This approach holds promise for the rational design of advanced capsules and emulsion droplets with tailored properties.