Synthesis of thermally stable Au-core/Pt-shell nanoparticles and their segregation behavior in diblock copolymer mixtures
We report a facile strategy for the preparation of sub-5 nm gold/platinum (Au-Pt) nanoparticles which are thermally stabilized by a crosslinked polymer shell. Diblock copolymer (PS-b-PI-SH) ligands on the Au nanoparticles were used to crosslink the vinyl functionalities on PI via hydrosilylation with 1,1,3,3-tetramethyldisiloxane in the presence of a platinum catalyst. The Pt catalyst was reduced on the Au nanoparticles during the hydrosilylation reaction resulting in the formation of a Pt-shell on the Au nanoparticle. The hydrosilylation reaction on the Au nanoparticles as well as their positioning in films of a poly(styrene-b-2-vinylpyridine) (PS-b-P2VP) block copolymer were thoroughly characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), UV-VIS spectroscopy, and X-ray photoelectron spectroscopy (XPS). Variables such as number of vinyl groups on PS-b-PI-SH ligands, the areal density of these ligands on the Au nanoparticle as well as the concentrations of the reactive species were varied systematically to obtain thermally stable nanoparticles. Au-Pt nanoparticles were stable in organic solvents up to 130 °C, and in polymer films at 190 °C for several days. This increased stability allowed the nanoparticles to be thermally annealed in films of PS-b-P2VP where their strong interfacial activity and localization were observed.