Formation of colloidosomes by adsorption of small charged oil droplets onto the surface of large oppositely charged oil droplets

This article describes the formation, stability and properties of oil-in-water emulsions consisting of large oil droplets with small oil droplets adsorbed to their surfaces. These “colloidosomes” were formed by mixing an oil-in-water emulsion containing relatively large anionic droplets (d32∼0.6 μm, β-lactoglobulin (β-Lg)–pectin coated, pH 4) with another oil-in-water emulsion containing relatively small cationic droplets (d32∼0.2 μm, β-Lg coated, pH 4). The ζ-potential, mean particle diameter and microstructure of the resulting composite emulsions were then measured. The ζ-potential of the particles went from negative (−30 mV) to positive (+25 mV) as the concentration of small cationic droplets was increased, indicating that they adsorbed to the surface of the large anionic droplets until they eventually saturated the surface. The composite emulsions were unstable to droplet aggregation at intermediate small droplet concentrations due to bridging flocculation and also at high small droplet concentrations possibly due to depletion flocculation. Nevertheless, relatively stable colloidosomes could be made over a range of small droplet concentrations, which consisted of large droplets surrounded by small droplets.