Polymer-Assisted Synthesis of Two-Dimensional Silver Meso-Structures

Dynamic Light Scattering and Small-Angle X-ray Scattering measurements, at different temperatures on a commercial polynaphthalene sulfonate dispersant (Daxad) dissolved in water, show the occurrence of poly-disperse domains with size between 10 and 20 rim. After addition of silver nitrate to Daxad aqueous solutions, the formation of new larger domains, coexisting with the smaller ones, takes place. Their growth is promoted by Ag+ ions that reduce the particle negative surface charge possibly also linking sulfonic groups of different small particles. Further on, upon addition of ascorbic acid as reducing agent, silver platelets, strips, and tabular hexagonal particles covered by the polynaphthalene sulfonate are formed at 5, 10, and 40 degrees C, respectively. The capacity of the polymer to cooperate with silver has been discussed and ascribed to the strong coordination of its sulfonic groups toward Ag+ ions and to a significant adsorption and stability on the resulting Ag-0 crystallites. The crystallite size, about 20 nm, is comparable with the size of Daxad domains observed by Small Angle X-ray Scattering and Dynamic Light Scattering measurements. This may indicate that crystallite size is determined by the size of Daxad domains constituting a sort of nanoreactor for the silver crystallite growth. Moreover, probably induced by the polymer coordination along preferential silver crystalline planes, silver crystallites assemble forming tabular hexagonal particles of about 200 nm, which, in turn, assemble building two-dimensional micrometer sized strips and platelets.