(257g) Dumbbell Particles As a New Type of Colloidal Emulsifier for Phase Transfer Delivery

The surface activity of colloidal particles have been recognized for a long time. However, the stabilization energy of isotropic particles at liquid-liquid interfaces sensitively depends on the contact angle of the particle at the interface. Therefore, Janus particles where the interfacial properties on two sides of the particles are very different have attracted much attention recently. Here, we develop a new type of Janus “structural emulsifier", i.e., polystyrene dumbbell particles, that possess different crosslinking densities in two lobes. They are initially hydrophilic and dispersible in water, but one of the lobes can be swollen gradually by oil (e.g., toluene) so that they become surface active upon contact with oil. By encapsulating molecules (e.g., dye and catalyst) into the uncrosslinked lobe of the polystyrene dimers, we further demonstrate that those dumbbell particles can be used for the delivery of active agents from water to oil phase in a controllable manner. The successful delivery is proved by subsequent catalytic reaction in the oil phase. Several advantages of this new type of emulsifier and delivery vehicle include: (1) the particles will only release materials when they are located at the interface. No leaking in water phase is observed at the initial stage, since the active molecules are constrained inside the polymeric particles; (2) compared with the isotropic particles, the surface properties of the dumbbell particles can be tuned on both lobes. For example, we can further coat one lobe with platinum so that they become self-propelling motors in hydrogen peroxide solutions; (3) the initial dispersity of the particles in water also ensure their high stability even with high salt concentrations. Therefore, our particles could be potentially used for colloidal surfactants in food industry, drug delivery, and enhanced oil recovery.