(106a) Self-Assembly of Nanoparticle Surfactants Harnessing Polymer Steric Interactions

Enhancing control over the assembly of nanoparticle building blocks is an area of great interest because ‘emergent’ properties arise that enable new applications in energy, imaging and medicine. Self-assembly has long been demonstrated a viable approach to drive button-up organization in amphiphilic systems including molecular surfactants and block-copolymers. In this talk, I will discuss progress made in our group towards the synthesis of nanoparticle surfactants that also self-assemble and cluster into ‘colloidal-molecules’ with controllable morphology. A scalable synthesis method was developed by tuning steric stabilization imparted by grafted polymers and short-ranged attractive interactions from molecular ligands. The phase behavior of nanoparticle surfactants has been explored and found to mimic, in certain aspects, the assembly of molecular surfactants. Cluster formation in these systems is analogous to micelle formation. Nanoparticle surfactants are also found to stabilize oil-water and air-water interfaces by adsorbing strongly and reducing the interfacial tension. The close arrangement of metallic particles in clusters and emulsions induce changes in optical absorption and local electric fields due to surface plasmon resonance. Specifically, near infrared (NIR) absorption is greatly enhanced in nano-Pickering emulsions. Small angle scattering (SAXS and SANS), optical spectroscopy, electron microscopy and dynamic light scattering are systematically utilized to decipher the influence of surface composition on the equilibrium structure of clusters in dispersion. We find that the cluster geometry is tuned by carefully controlling steric interactions of the absorbed polymer at the surface. This new assembly method is extremely simple, inexpensive, and general without requiring any specialized polymer chemistry. Self-assembly of surfactant nanoparticles represents a powerful platform to form diverse nanostructures and colloidal materials with novel properties.