Facile and Scalable Preparation of Solid Silver Nanoparticles (<10 nm) for Flexible Electronics

Metal conductive ink for flexible electroncs has exhibited a promising future recently. Here, an innovative strategy was reported to synthesize silver nanocolloid (2.5 +/- 0.5 nm) and separate solid silver nanoparticles (<10 nm) effectively. Specifically, silver nitrate (AgNO3) was used as a silver precursor, sodium borohydride (NaBH4) as a reducing agent, fatty acid (CnH(2n+1)COOH) as a dispersant agent, and ammonia (NH3 center dot H2O) and hydrochloride (HCl) as a pH regulator and complexing agent in aqueous solution. The main mechanism is the solubility changes of fatty acid salts (CnH(2n+1) COO-NH4+) and fatty acid (CnH2n+1COOH) coated on the synthesized silver nanoparticles (NPs) in aqueous solution. This change determines the suspension and precipitation of silver NPs directly. The results show that when n in dispersant is 12 and molar ratio (C12H24O2/AgNO3) is 1.0, the separation yield of silver NPs is up to 94.8%. After sintering at 125 degrees C for 20 min, the as-prepared conductive silver nanoink (20 wt %) presents a satisfactory resistivity (as low as 6.6 mu Omega.cm on the polyester PET substrate), about 4 times the bulk silver. In addition, the efficacy of the as-prepared conductive ink was verified with the construction of a radio frequency antenna by inkjet printing and conductive character pattern (Fudan-Fudan) by direct wiring, showing excellent electrical performance.