Shape Variations and Control in Self-Assembled Metal Nanoclusters
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Shape Variations and Control in Self-Assembled Metal Nanoclusters M. Zubrisa, M. Solimandoa,b, E. P. Goldbergb, S. Reichc, and R. Tannenbauma* a
School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA; bDepartment of Materials Science and Engineering, University of Florida, Gainesville, FL 32611, USA; cDepartment of Materials and Interfaces, Weizmann Institute of Science, Rehovot 76100, ISRAEL ABSTRACT The selective interaction of metal clusters with various polymers constitutes the basis for the self-assembly approach to the synthesis of organic-inorganic hybrid materials, that leads to the control of particle size, geometry and dispersion gradient. Metal particles were synthesized by the thermal decomposition of an organometallic precursor, in this case, iron pentacarbonyl, in the presence of a polymer matrix. Under the conditions utilized for these reactions, the aggregation of the metallic clusters competed with the interactions between the growing metal fragments and the polymer matrix. The dominance of one reaction route as compared to the other, ultimately determined the equilibrium particle shape, size and distribution for each metal-polymer system. In this work, we attempted to analyze the formation of iron oxide nanoclusters in several structurallydistinct polymers, and developed a general mechanistic view to explain the characteristics of the polymer-metal oxide hybrid materials that were obtained. INTRODUCTION Self–assembly represents a key approach to hierarchical ordering through length scales, where material properties at the molecular level determine the structure at the nanoscale, which further determines material characteristics at the mesoscale [1]. This results in unique materials properties, which cannot be achieved in disordered, or partially disordered systems. Such an approach has been applied to the synthesis of organicinorganic nanocomposite structures, whereby metallic particles have been selectively incorporated into polymer matrices, and in turn, the polymer moiety has effectively controlled the size and shape of the particles. The ability to control particle size, size distribution, morphology, geometry and dispersion, directly translates to an ability to control the material properties of the polymer-metal nano-cluster composites [2-4]. Some studies have shown that metal nano-cluster formation is, indeed, sensitive to the presence of polymers during the synthesis process [5-7]. For example, Tang et al. [8] have shown that the size distribution of copper clusters formed in a polymer matrix host was narrow, centered on clusters of order 10 nm, while Pitcher et al. [9] produced novel morphologies of lead-sulfide in polyethylineoxide. Tannenbaum [10], Rotstein et al. [11] and Rotstein and Tannenbaum [12] have shown that both the mechanism of metal cluster formation and the equilibrium cluster size and cluster size distribution is a direct function of polymer concentration in the immediate environment of the cluster-forming process. Howe
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