Preparation and characterization of polymer-stabilized rhodium sols. I. Factors affecting particle size

Preparation and characterization of polymer-stabilized rhodium sols with average metal particle diameters between 1 nm and 3.5 nm are described. The interaction of the rhodium ions with the polar polymer before reduction is one of the most important factors in preparing stable metal sols. With poly(ethylene oxide) the interaction was so weak that only large metal particles precipitated and with polyethyleneimine the interaction was so strong that the precursor could not be reduced. The best polymers were polyvinyl-2-pyrrolidone (PVP) and poly-2-ethyloxazoline. With PVP as a stabilizer it was shown that the reduction rate determined the particle size. The primary particle size in the final sol was the smallest when hydrogen was used as a reducing agent and l-butanol as a solvent. When colloids were prepared in an alcohol/water mixture in which the alcohol functions as a reducing agent, the size increased with increasing molecular weight of the alcohol. The stability of the colloids decreased with increasing solubility of the polymer.