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 (φm) was estimated as φm=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 φm 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.