Mayonnaise is a prime example of an emulsion that consists of a water phase and an oil phase. Oil and vinegar are mixed to form countless droplets. Egg yolk is added as an emulsifier that coats the surface of the droplets, and thereby acts to stabilise them. Done correctly, a fine, creamy mixture is formed. If the oil is added too quickly (or at the wrong time), the mayonnaise congeals: the droplets aren't stable enough, they dissolve, and the phases separate.
So far materials researchers have had just as much trouble as amateur chefs have trying to make the perfect mayonnaise in producing controlled interfaces of droplets in two-phase mixtures with stabilisers or emulsifiers. These "reinforced" interfaces are important because they stabilise the droplets and ultimately the respective emulsion. Until now, researchers have not managed to successfully regulate either the extent of the particle coverage or the composition of the particles in the interfaces of such droplets.