Metallic Nanoparticles from Single Polyelectrolyte Molecules
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Metallic Nanoparticles from Single Polyelectrolyte Molecules Ganna Gorodyska, Anton Kiriy, Sergiy Minko, and Manfred Stamm Institut für Polymerforschung Dresden, Hohe Strasse 6, 01069 Dresden, Germany ABSTRACT Here we report on the metallization of poly(2-vinylpyridine) (P2VP) by coordination with palladium acetate (PA) followed by reduction with dimethylamine borane (DAB) to metallic palladium. The morphology of the resulting products deposited on a flat surface was analyzed with AFM. If P2VP, PA and DAB are mixed together, the Pd clusters up to 30 nm in diameter are obtained. A two step synthetic procedure was examined. The initially prepared complex P2VPH-1/2(PdCl4) was deposited on Si-wafer and then reduced, leading to the Pd clusters with a narrow size distribution (3 nm height by 100 nm length). Alternately, a step-by-step procedure was used wherein P2VP single molecules were deposited on Si wafers from very dilute acidic aqueous solutions then placed in PA solution and finally reduced with DAB, resulting in the 1.55 nm in the diameter wire-shaped Pd nanoparticles with the length of about 350 nm. INTRODUCTION Metal particles with dimensions of the order of nanometers are of great interest due to their unique electrical [1], optical [2], magnetic [3], and catalytic [4] properties. The stabilization of nanoparticles (NP) to prevent them from aggregation is one of essential research tasks. Several routes to solve this problem using surfactants or diblock copolymers [5,6] have recently been developed. Near spherical metal NP which are incorporated in block copolymer micelles or in a polymer matrix were obtained using these methods. Design of NP with a more complicated and definite shape is a considerably more difficult problem. The template synthesis [7] involves the deposition of metals into the particular shaped host material (usually inside a porous matrix, e.g. carbon nanotubes or rod-like micelles) and is considered to be one of the most important methods of the NP fabrication. Recently, DNA has been successfully used as a biotemplate [8] for the fabrication of metallic nanowires from single molecules. The synthesis is based on a twostep procedure which involves binding of metals (Pd or Ag) to DNA followed by their chemical reduction. The procedure results in 20-100 nm in the diameter metallic wires, which are, however, much larger than the 2 nm assumed for the diameter of a single DNA molecule. The vacuum evaporation method was used to deposit gold on single extended DNA strands to produce wires < 10 nm in width and with lengths up to 60 nm. On the other hand, polymer chemistry offers a fascinating world of different architectures and structures of molecular entities: ranging from stars, rods to branched, hyper-branched or Hshaped polymer molecules nearly of all possible architectures. It would be a challenging task to utilize those structures for the generation of nanoparticles, which then could serve specific tasks controlled by topology. This concept might be a route to a nanomachine consisting of a singl
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