Particles At Liquid Interfaces: Effects of Particle Charge and Their Consequences for Particle-Stabilized Emulsions

It has been known for more than a century that colloidal particles with the "right" wetting properties can stabilize emulsions, much like surfactants or amphiphilic polymers do. Today, particle-stabilized emulsions (so-called Pickering emulsions) play an important role in many industrial applications, but our fundamental understanding of the connection between particle properties and emulsion characteristics is still surprisingly poor. We can, for example, prepare an emulsion by mixing equal amounts of an oil phase and an aqueous particle dispersion; but even with complete knowledge of both liquids and all particle properties, current theory fails to predict reliably the stability and even the type (w/o or o/w) of the emulsion formed.

This presentation will discuss electrostatic sources of such difficulties and propose several steps toward an improved theoretical description and better practical control of emulsion properties. In particular, we will address the role of electrostatic interactions between a particle and a liquid interface before and after particle adsorption, and show that widely neglected image charge effects can prevent particle adsorption and emulsion stabilization altogether. For the case of successful particle adsorption, the particle's contact angle with the interface is found to be influenced strongly by the particle charge in ways that are not usually accounted for, but have important consequences for the long term stability of Pickering emulsions.