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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.

Monolayer-protected silver nanoparticles were directly synthesized in a highly concentrated organic phase (>2 M) and then printed into conductive lines on polyimide by a drop-on-demand inkjet printer. The fully organic phase system contains silver nitrate as a silver precursor, n-butylamine as a media dissolving silver salt, dodecanoic acid as a capping molecule, toluene as a solvent, and sodium borohydride as a reducing reagent. Even using only generic chemicals, monodispersed silver nanocrystals with size of 7 nm were easily synthesized at the 100 g scale in a 1 litre reactor. Hydrocarbon monolayer-protected silver nanocrystal showed excellent dispersion stability even at metal content >70 wt%. The silver ink with metal content of 33 wt% had a viscosity of 5.4 cP and surface tension of 25 dyn cm−1. The silver ink was successfully inkjetted on variable substrates and then metallized at 250 °C. The metallized silver patterns exhibited very low specific electrical resistance (6 µΩ cm)

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.