Polymer-Mediated Particle Coarsening within Hollow Silica Shell Nanoreactors

Inspired by the scanning probe block copolymer lithography process, hollow silica shells were loaded with polymer-metal ink mixtures and investigated as solution-based nanoreactors for the synthesis of gold nanoparticles. The incorporation of poly(ethylene oxide) (PEO) into these hollow silica nanoreactors (approximately 40 nm in size) and the use of a two-step reductive annealing process (first at 200 degrees C and then at 600 degrees C) results in a high yield (76%) of larger (-,6 nm) single nanoparticles; when the polymer is not used, smaller (-,3 nm) particles dominate, and the yield of single particles is only 6%. It was determined that particle coarsening mostly occurs in the temperature range where the polymer is present and not degraded (i.e., <400 degrees C for PEO), as indicted by correlative in situ scanning/transmission electron microscopy in a reductive gas-phase environment. Thus, polymer incorporation in this nanoreactor system, which is amenable to scale up, drives the complete conversion of nanoreactor contents without excessive metal loss, highlighting the impact of nanoreactor composition and structural design on particle synthesis.