Self-Assembly of Amphiphilic Janus Particles at Oil/Water Interfaces

Recent experimental developments have led to a variety of easily scalable techniques for the synthesis of morphologically and chemically anisotropic polymer colloids. One such technique, seeded emulsion polymerization (SEP), has been used to produce a variety of amphiphilic polymer Janus particles for use as pH responsive solid surfactants. These studies have led to an understanding of the emulsification behavior of these colloids and factors controlling emulsion type and size. However, there has been less work focused on understanding the mechanism and factors governing the interfacial assembly of Janus particles. We investigated the interfacial behavior of these chemically and morphologically heterogeneous polymer colloids using pendant drop tensiometry. Systematic studies were performed as a function of colloid concentration, system pH, and colloid morphology. The interfacial behavior of these systems was found to be not only sensitive to their environmental conditions, but also to the type and degree of anisotropy. Our studies elucidate the way these anisotropic colloids adsorb to and assemble at the interface and re-arrange to maximize the reduction of the interfacial tension.