Hetero-Aggregates as Particulate Emulsifiers and the Role of Surface Roughness

Particles adsorbed to the surface of emulsion droplets act as emulsifiers and stabilizers in so-called Pickering emulsions. Surface roughness has been proposed as one of the key parameters determining the particles' emulsifying properties, but some confusion persists about its true impact: although surface roughness reportedly lessens a particle's ability to stabilize emulsion droplets, weakly flocculated particles with their intrinsic aggregate roughness have been hailed as ideal Pickering emulsifiers. Here we report systematic studies on particles with tunable roughness. These particles consist of a micron-sized core decorated with oppositely charged polymer nanoparticles that can be dissolved by pH adjustment and adsorbed to the same core in the form of a smooth macromolecular film. Progressive dissolution of the adsorbed pH-responsive nanoparticles leads to continuous degrees of surface roughness while maintaining the same surface chemistry. We discuss the observed effect of varying particle roughness on wetting and emulsification properties.