| In the present study, colloid-solder core-shell particles are synthesized, characterized and thermally sintered (reflowed) to form two types of 3-dimensional (3D) ordered particles. Polystyrene (PS) colloidal seeds in the size range of 0.1--1 microm were first synthesized by an emulsion polymerization. These micron to sub-micron size particles were then treated with a thiol coupling agent to facilitate solder metal deposition on the particle surface. The formation of the solder (low melting metals or metal alloys) shell on colloidal seeds was realized by metal ion reduction using a reducing agent in the presence of a surfactant. The thiol played an important role in the formation of core-shell particles. In addition, by simply adjusting the thiol concentration, we were able to obtain different solder coverage on the colloidal particles. The solder shell formation was evaluated by monitoring particle growth and confirmed by elemental analysis through energy dispersive X-ray spectroscopy (EDS). Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) show uniform surface coverage on the polystyrene seeds. Fourier transform infra-red (FT/IR) spectroscopic measurements of the core-shell composite particles show the presence of sulfide groups in the particles, which provides valuable insight on the mechanism for coating of solder on colloidal particles. Both tin (Sn) and tin/indium (Sn/In) solder materials have been successfully synthesized onto colloidal particles. After being sintered (reflowed) at temperatures ranging from 150--300°C a drastic change in morphology was observed and two types of assembled structures were formed. At 150°C, the solder layer deformed and bonded polystyrene (PS) colloidal particles together, forming mechanically stable structures, while the colloidal particles were still intact. At 300°C a mesoporous tin oxide film was obtained by decomposition of the polystyrene seeds, providing a new way to form mesoporous structures with high surface area, which is promising as a new sensing or catalytic material.Keywords: Colloidal particles, solder, core-shell, self-assembly, mesoporous structures. |
