Improved stability and film formability of oil-based silver nanoparticle suspensions by addition of polystyrene

In this study, we focused on how to develop an oil-based stable suspension of conductive silver ink and improve its film formability on the substrate. Silver nanoparticles (Ag-NPs) were first prepared in water with addition of oleic acid (OA) and butyl amine (BA) as co-stabilizing agents. The water medium was then replaced by an organic solvent to prepare the organic silver conductive ink. The synthesized Ag-NPs with an average particle size of about 13.3 nm were stabilized by steric hindrance of the attached OA − as proved by FTIR analysis and surface zeta potential. The Ag-NPs had higher stability in cyclohexane than in hexane, owing to the increased interaction between the long alkyl chain in OA − and cyclohexane. The stability was more than one year in cyclohexane with little change in particle size. Conductive films were obtained by drop-coating the organic Ag-NP inks on glass slide and sintering up to 250 °C. Moreover, addition of polystyrene at 1 wt % into the cyclohexane increased the wettability of conductive ink on the substrate and improved the film formability and integrity while preventing oxidation during sintering. A uniform and hydrophobic Ag-NP film was obtained with a sheet resistance of 0.64 Ω/Sq.