(471j) Directed Assembly of Highly Hydrophilic and Highly Hydrophobic Particles for Stabilizing Emulsions
Particles that are partially wettable in two immiscible liquids are usually required to form stable emulsions. Here, we begin with completely hydrophilic and highly hydrophobic particles that do not, by themselves, form emulsions. When these particles are suspended in aqueous and organic phases respectively, and the two suspensions mixed, attractive Van der Waals forces between these types of particles cause them to assemble physically into entities that are partially wettable in both phases. These entities are very effective at stabilizing emulsions. Particle type as well as choice of liquids are all important for creating the physically assembled particulate entities that stabilize emulsions. We use hydrophobic fumed silica particles and either carbon black or iron oxide particles as their hydrophilic counterparts to form stable toluene-in-water and water-in-toluene emulsions. This provides a new route for generating emulsions without any processing steps to make particles partially wettable for this purpose. It can be used as a platform for the development of new materials with particles bearing different physical and chemical properties assembling at oil-water interfaces to stabilize one immiscible liquid in another.