Visualization of Isolated Poly(2-vinylpyridine)-<i>b</i><i>lock</i>-Polyisoprene Chains Adhered to Isolated Palladium Nanoparticles

Abstract

Isolated polymer chains adhered to isolated metal nanoparticles were directly visualized and characterized by atomic force microscopy (AFM) in order to gain insight into the stabilizing mechanism of the nanoparticles and their potential surface activities. For this purpose, nanoscaled Pd particles adhered and stabilized by poly(2-vinylpyridine)-block-polyisoprene (P2VP-b-PI), designated as Pd-(P2VP-b-PI), were prepared by reducing Pd2+ ions with 1-propanol at 85 °C for 45 h in a dilute solution of P2VP-b-PI and palladium acetylacetonate in benzene as a solvent and 1-propanol as a reducing agent. Thus, prepared Pd-(P2VP-b-PI) were purified to remove free P2VP-b-PI and unreacted salt, dissolved into a very dilute benzene solution containing ∼10-5 wt % of the particles, and transferred onto mica surface by dipping a sheet of mica into the solution. The surface of the sheet was further washed gently with a few drops (∼0.1 mL/drop) of the benzene to obtain isolated Pd-(P2VP-b-PI) on the surface and observed by AFM with a tapping mode. The AFM images show isolated Pd-(P2VP-b-PI) with an average diameter of Pd particles of 8 nm and one to three adhered P2VP-b-PI chains. It was also revealed that only a part of segments of the chains adhered to the particles so that the particles had still a large surface area free from the polymers, and the adhered polymers had subchains free from the particles, thus stabilizing against coalescence of the particles due to entropic repulsion.