SMALL-ANGLE X-RAY-SCATTERING ANALYSIS OF POLYMER-PROTECTED PLATINUM, RHODIUM, AND PLATINUM RHODIUM COLLOIDAL DISPERSIONS/

Formations of poly(N-vinyl-2-pyrrolidone) (PVP)-metal ion (Pt, Ph or P t/Rh(1/1)) complexes in H2O/C2H5OH (''polymer-metal ion complexes'') b efore alcohol-reduction and PVP-Pt, Rh, or Pt/Rh(1/1) metal cluster (' 'polymer-metal cluster'') after alcohol-reduction were studied by smal l-angle x-ray scattering (SAXS). SAXS intensity of the solution contai ning polymer-metal ion complexes is higher than that of the reference polymer solution without metal ions, suggesting that concentration flu ctuations of polymer segments are enhanced due to the formation of pol ymer-metal ion complexes. Spatial distributions of metal clusters in c olloidal dispersions are different from each other among the cases of Pt, Ph, and Pt/Rh(1/1) colloidal dispersions. The superstructure (grea ter than 10.0 nm in diameter), whose average sizes highly depend on th e metal element employed, are formed. These superstructures are compos ed of several fundamental clusters with a diameter of similar to 2.0-4 .0 nm. Colloidal dispersions of Ph form a percolation network of clust ers with an average period of similar to 6.0 nm inside the higher-orde r organization of its superstructure. Experimental results concerning the physical aging show the high stability of colloidal dispersions of metal clusters protected by water-soluble PVP. (C) 1998 American Inst itute of Physics. [S0021-9606(98)51437-7]