(742d) Synthesis and Self-Assembly of Nanoparticle Surfactants

A simple method is presented for the synthesis of amphiphilic gold nanoparticle surfactants that self-assemble into clusters of controllable structure. The synthesis technique is based on the sequential functionalization of the surface with thiol terminated polyethylene glycol (PEG) to sterically stabilize particles in water and short alkane-thiols rendering the particles amphiphilic. The nanoparticle surfactants are surface active and form rafts at the air-water interface and stable nanoparticle clusters of controllable size and shape in dispersion. The clusters are also reminiscent of micelles formed from molecular surfactants with aggregation numbers that can be controlled via the modification of the grafting density of the polymer on the nanoparticle surface. The nanoparticle surfactants are also shown to be highly effective emulsifying agents due to their high adsorption energy at oil-water and air-water interfaces and they form stable colloidosomes that are stable against coalescence. Both the clusters and the colloidosomes that are formed from these particles exhibit tunable shifts in plasmon resonance and show enhanced near-infrared optical absorption. This makes them useful for a wide range of applications in medicine and energy.