Structure of microparticles and nanoparticles in solid-stabilized emulsions

Emulsions of oil and water stabilized by adsorbed solid particles are known as solid-stabilized emulsions (often referred to as Pickering emulsions). Using confocal microscopy and environmental transmission electron microscopy, we have studied the self-assembly of colloidal-sized polystyrene particles and alkanethiol-capped silver nanopaticles in Pickering emulsions. Colloidal samples of monodisperse size, when exposed to the emulsion at low concentrations, were found to form small patches with local hexagonal order; these crystalline domains were separated by other particle-free domains. Polystyrene particles with different sizes (1 micron and 4 microns) and different wettability could simultaneously segregate to the emulsion interface and form mixtures on it. In contrast to microparticles that form monolayers, the dodecanethiol-capped silver nanoparticles of 1-5 nm form randomly distributed multilayers at the Pickering emulsion interface, with an interparticle distance varying from close contact to approximately 25 nm. Our work offers the first direct observation of nanoparticles in a liquid medium using the environmental transmission electron microscope (E-TEM).