Dispersion and rheology of nickel nanoparticle inks

Nickel nanoparticles were dispersed in α-terpineol solvents, and their rheological behaviour and suspension structure were examined using various organic surfactants, surfactant concentrations (0–10 wt.% of the powder) and solids loadings (φ=0.01–0.28 in volumetric ratios) over a shear-rate range 10⁰–10³ s⁻¹. A surfactant of oligomer polyester was found effective in the nanoparticle dispersion. An optimal surfactant concentration ca. 2–4 wt.% of the solids was found; beyond which, the apparent viscosity increased adversely. The oligomer-polyester molecules appeared to adsorb preferentially on the nanoparticle surface, forming a steric layer which facilitates the ink flow for the improved dispersion. A pseudoplastic flow behaviour was found as shear rate increased, and a maximum solids concentration (φ_m) was estimated as φ_m=0.32. The interparticle potential was dominated by van der Waals attraction in the terpineol liquid, and a reaction-limited cluster aggregation (RLCA) featuring with a fractal dimension (D _f) of 2.0 was calculated. This finding together with the reduced φ_m reveals that the nanoparticle inks were flocculated in character even with the presence of polyester surfactant. Additionally, a porous (electrically conductive) particulate network was expected to form if the inks were printed on a non-conductive substrate followed then by drying and sintering in practice.