Charged hydrophobic colloids at an oil-aqueous phase interface

Area of Science:

• Colloid and surface science
• Soft matter physics
• Interfacial phenomena

Background:

• Hydrophobic poly(methyl methacrylate) (PMMA) particles in high dielectric constant oils acquire significant charge.
• Image-charge effects at oil-water interfaces cause strong particle binding, despite minimal wetting by the aqueous phase.

Purpose of the Study:

• To investigate the behavior and interactions of charged colloidal particles at an oil-water interface.
• To isolate and study interactions solely due to particle surface charging in oil.
• To validate a simple image-charge model for interfacially bound particles.

Main Methods:

• Observation of individual colloidal particle behavior approaching an interface.
• Analysis of interactions between interfacially bound particles.
• Utilizing minimally wetted particles to isolate charging effects.

Main Results:

• Demonstrated strong binding of charged PMMA particles to the interface via image-charge effects.
• Isolated and studied inter-particle interactions arising purely from surface charge.
• Showed that particle charge (q) is the sole fitting parameter in a simple image-charge model.

Conclusions:

• Image-charge effects are dominant in binding hydrophobic colloidal particles to conducting aqueous interfaces.
• Interactions between these interfacially bound particles can be accurately described by a basic image-charge model.
• The particle charge is the critical parameter for understanding these interfacial interactions.