A small angle scattering study of dendrimer-copper sulfide nanocomposites

Dendrimers are a new class of three-dimensional, man-made molecules produce d by an unusual synthetic route which incorporates repetitive branching seq uences to create a unique novel architecture. Exceptional features of the d endritic architecture include a high degree of structural symmetry, a densi ty gradient displaying an intra-molecular minimum value and a well defined number of terminal groups which may be chemically different from the interi or. The combination of these features creates an environment within the den drimer molecule which facilitates trapping of guest species. Recently, dend ritic polymers have been used as soluble templates/unimolecular reactors fr om which nano-clusters of inorganic compounds or elements can be synthesize d. The basic concept involves using dendrimers as hosts to preorganize smal l molecules or metal ions, followed by a simple in situ reaction which will immobilize and stabilize domains of atomic or molecular guest components ( inorganic compounds as well as elemental metals). In one of these examples poly(amidoamine) (PAMAM) dendrimers have been used, to attract copper(II) i ons inside the macromolecules where they are subsequently reacted with solu bilized H2S to form metal sulfides. These organic/inorganic, dendrimer-base d hybrid species have been termed 'nanocomposites' and display unusual prop erties. For example, solubility of the nanocomposites is determined by the properties of the host dendrimer molecules. This allows for solubilization of the inorganic guest compounds in environments in which they are inherent ly insoluble. Since it has been established that there is no covalent bond between host and guest, these observations suggest that the inorganics are physically and spatially restricted by the dendrimer shell. However, this s tructure has not been verified. In this investigation a preliminary underst anding of the physical structure of these dendrimer-based nanocomposites wa s sought. A model system of PAMAM dendrimer-copper sulfide nanocomposites w as studied in various stages of its formation using a combination of small angle X-ray and neutron scattering experiments. The results suggest that li ttle perturbation of the dendritic species occurs on complexation, but indi cate that a secondary super-molecular aggregation phenomena occurs within n anocomposite solutions. (C) 1999 Published by Elsevier Science Ltd. All rig hts reserved.