Self-Assembly of Metal Nanoclusters in Block Co-Polymers
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Self-Assembly of Metal Nanoclusters in Block Co-Polymers Erica H. Tadd1, John Bradley1, Eugene P. Goldberg2 and Rina Tannenbaum1* 1 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332. 2Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611. ABSTRACT This paper describes the formation of cobalt and iron metal nanoclusters in various polymeric domains. The size of the particles, their size distribution and their geometry is controlled by the extent of the interfacial interactions between the polymeric phase and the growing metal fragments. Iron oxide particles are shown to exhibit various geometries as a function of the polymer medium and the temperature at which they are formed. The selective phase separation and particle confinement of cobalt clusters in the presence of PS25300-b-PMMA25900 block co-polymer was achieved due to the different reactivities of the functional groups in the blocks towards the metal fragments. Transmission electron micrographs showed that cobalt clusters aggregated primarily in the poly(methyl methacrylate) block, while no cobalt nanoclusters were observed in the polystyrene block, thus creating a patterned distribution that coincided with the morphology of the block copolymer. INTRODUCTION Hierarchical materials are ordered on the molecular (10-100Å), nano (10nm100nm) and meso (1mm-10mm) scales. This unique level of organization leads to specialized material properties that significantly differ from those of less ordered phases. However, optimal performance requires a degree of control over domain size and distribution, on all length-scales, which is not easily obtainable with current synthetic methods. The development of a synthesis methodology to control the structure and properties of metallic nanocluster-polymeric composites requires detailed understanding of the interactions between the metal clusters and their polymeric environment, as well as the relationship between polymeric parameters and cluster formation. Although various studies have shown that polymers control cluster formation and properties [1-4], little is known regarding the details of this relationship. The large number of parameters (e.g. polymer molecular weight, chemistry and concentration) requires a systematic investigation. This paper describes the development of a versatile and controllable synthetic process for the formation of three-dimensional, self-assembled nanoparticle arrays in, and aided by, a polymeric medium. The development of appropriate synthetic and processing methods, which can produce finite, ordered domains with a given geometry, is a central theme in the design of hierarchical ordered structures [5-8]. EXPERIMENTAL METHOD The solution decomposition of Co2(CO)8 and Fe(CO)5 to metal nanoclusters was performed in a sealed three-neck round-bottomed reaction vessel that was first evacuated and then flushed with N2. A side neck was equipped with a thermometer, the middle neck with a reflux condenser, and the other neck
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