Nanocomposites and nanomaterials

Effect of the structure of silica/polyacrylamide hybrids on cobalt nanoparticles formation
Permyakova N.M. 1, Fomenko A.S. 1, Zheltonozhskaya T.B.1, Klepko V.V. 1, Klymchuk D.O. 2
1 Department of Polymer Physics, Institute of Macromolecular Chemistry of the NAS of Ukraine. 48 Kharkivske Shosse, Kyiv-02160, Ukraine.
E-mail: permyakova@ukr.net
2 M.G. Kholodny Institute of Botany of the NAS of Ukraine, 2 Tereshchenkovska St., 01601 Kyiv, Ukraine.

Nanostructured materials exhibit new properties that differ markedly from those of the corresponding bulk solid due to the small size effect. Cobalt nanoparticles (CoNPs) have received considerable attention due to their outstanding magnetic properties as ferromagnetic materials. The current work presents a simple and efficient method for preparing CoNPs in aqueous media using polymer/inorganic hybrids (PIHs) based on silica nanoparticles and grafted polyacrylamide chains (SiO2/PAAm).
Three PIH samples with different number and length (molecular weight) of the grafted PAAm chains per inorganic particle were synthesized by free-radical grafting polymerization of acrylamide from the unmodified surface of SiO2 nanoparticles. The detailed structure of the resulting hybrids was established using elemental analysis, DTGA, static light scattering, viscometry and TEM. These PIH samples proved to be effective matrices for in situ synthesis of CoNPs.
The processes of borohydride reduction of Co-salt to nanoparticles in pure water and aqueous solutions of PIH were studied depending on the concentration of PIH and metal salt (and reducing agent) using photography, UV-visible spectroscopy, TEM and WAXS. A special approach to characterizing the kinetics and efficiency of CoNPs formation in pure water and hybrid solutions using UV-Vis spectroscopy has been proposed and implemented. Due to this, the kinetic parameters of the CoNP formation process (accumulation rate and yield of the obtained CoNPs) were determined. It was revealed that among the PIH samples, the most intense process of CoNPs formation developed in hybrid matrices with a rather loose "corona" of grafted PAAm chains. The morphology of the CoNPs/PIH compositions is represented mainly by individual swollen hybrid particles with a size of ~9-35 nm containing metal nanoparticles with a size of ~1-7 nm. Thus, individual particles of hybrid matrix with CoNPs can be considered as the basic structural elements of such a nanocomposite in solution.