Kwi Jong Lee

Environmentally friendly synthesis of organic-soluble silver nanoparticles for printed electronics

In this study, we attempted to synthesize organic-soluble silver nanoparticles in the concentrated organic phase with an environmentally friendly method. The fully organic phase system contains silver acetate as a silver precursor, oleic acid as both a medium and a capping molecule, and tin acetate as a reducing agent. Monodisperse silver nanoparticles with average diameters of ca. 5 nm can be easily synthesized at large scale. Only a small usage of tin acetate ( 90%). Also, it was investigated that the residual tin atom does not exist in the synthesized silver nanoparticles. This implied that tin acetate acts as a reducing catalyst.

Large-Scale Synthesis of Polymer-Stabilized Silver Nanoparticles

The synthesis and characterization of polymer-stabilized silver nanoparticles (Ag NPs) for water-based silver inks are studied. In order to synthesize Ag NPs with spherical shape, the conventional polyol processes require an excess of poly(vinyl pyrrolidone) (PVP) (10 ~ 1000 times than AgNO3) and therefore result in low productivity per reactor volume. In this study, poly(acrylic acid) (PAA) with carboxylic acid group was used instead of PVP. Even at less molar ratio of PAA to AgNO3 (< 2), the spherical Ag NPs with average size of 30 nm were successfully synthesized at 100 gram-scale with high reaction yield of 90%. Furthermore, the Ag NPs were dispersed into alcohol-based solvent and then patterned into metallic lines through inkjet printing technology.

Preparation of Nickel Nanoparticles in Water-in-Oil Microemulsion

Nickel nanoparticles were prepared by reduction of nickel-hydrazine complex with sodium borohydride (NaBH4) in water-in-oil (w/o) microemulsion of PVP/ethanol/toluene/water at 50C. It was investigated through SEM and TEM photographs that the nickel nanoparticles with a diameter 15~20nm were nearly monodispersed. By the analysis of XRD, the resulting particles were characterized to be pure crystalline nickel with a face-centered cubic structure. The results indicate that the size, shape and distribution of particles depend on the mole ratio of [water]/[PVP] and [NaBH4]/[Ni]. Also, it was found that particle size could be controlled by the kinds of surfactants.

Synthesis of High Concentration Cuprous Oxide Nanoparticles by Modified Polyol Process

Cuprous oxide nanoparticles at high concentration (up to 0.3M) were successfully synthesized by modified polyol process. The redispersion stability could be controlled by optimizing various conditions like polymer concentration, temperature, reductant, and catalyst. Reductant and catalyst play a crucial rule in redispersion of cuprous nanoparticles. Under poor conditions, particles grow to larger sizes due to aggregation of nanoparticles. This modified polyol process allows monodispersed cuprous oxide to be obtained on gram scale in a single reaction and make possible a high synthetic yield of more than 80%.