Creating High Yield Stress Particle-Laden Oil/Water Interfaces Using Charge Bidispersity

Area of Science:

• Colloid and Interface Science
• Materials Science
• Rheology

Background:

• Pickering emulsions are stabilized by particles at oil/water interfaces.
• Current methods often require high particle concentrations for effective stabilization.
• Interfacial viscoelasticity plays a role, but steric hindrance is typically dominant.

Purpose of the Study:

• To investigate if bidisperse (two-sized) charged particles can create high interfacial viscoelastic yield stresses at low concentrations (<50%).
• To evaluate the efficacy of bidisperse particle systems for Pickering emulsion stabilization.
• To compare the performance of bidisperse systems against monodisperse systems and theoretical models.

Main Methods:

• Interfacial rheology experiments were performed at oil/water interfaces.
• Visualization experiments were conducted using charged latex spheres (amidine, carboxylate, sulfate-coated).
• A model based on interparticle forces was developed and compared with experimental data.

Main Results:

• Bidisperse particle systems formed more networked interfacial structures compared to monodisperse systems.
• At <50% surface concentration, bidisperse interfaces exhibited viscoelastic moduli approximately one order of magnitude higher than monodisperse interfaces.
• Bidisperse interfaces showed measurable yield stresses (∼10⁻⁴ Pa·m), while monodisperse systems did not.
• The enhanced viscoelasticity was attributed to increased interparticle attraction, not microstructural changes.

Conclusions:

• Bidisperse particle systems can generate significant interfacial viscoelastic moduli and yield stresses at low particle surface concentrations.
• This approach offers a potential strategy for more efficient Pickering emulsion stabilization.
• The findings suggest fewer particles may be needed in future applications, reducing cost and environmental impact.