Dispersion and rheology of nickel nanoparticle inks

Nickel nanoparticles were dispersed in a-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 (phi=0.01-0.28 in volumetric ratios) over a shear-rate range 10(0)-10(3) 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 pseucloplastic flow behaviour was found as shear rate increased, and a maximum solids concentration (phi(m)) was estimated as phi(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 phi(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. (c) 2006 Springer Science + Business Media, Inc.