Bottom-Up and Top-Down Approaches to the Synthesis of Monodispersed Spherical Colloids of Low Melting-Point Metals

We report two different, solution-based approaches that have allowed us to process metals with melting points below 400 °C as monodispersed spherical colloids, in copious quantities, and with diameters controllable in the range of 100 to 600 nm. Bismuth was selected as a typical example to demonstrate the concepts. The production of monodispersed bismuth particles was realized by either thermally decomposing bismuth acetate in boiling ethylene glycol (the bottom-up approach) or by emulsifying molten drops of bismuth in boiling di(ethylene glycol) (the top-down approach), followed by quenching with cold ethanol. Depending on the concentration of Bi precursor and the stirring rate, the diameters of these uniform spherical colloids could be readily varied from 100 to 600 nm. The synthetic protocols have also been extended to prepare uniform spherical colloids from other metals with relatively low melting points, and typical examples include Pb, In, Sn, Cd, and their alloys.