Effect of polymeric surfactant on flow behaviors of nickel–ethanol–isopropanol suspensions

Influence of a non-ionic, polymeric surfactant to the rheology and suspension structure of nickel (Ni) powders dispersed in ethanol–isopropanol solvents has been examined over a range of volumetric solids loadings (φ=0.05–0.25), surfactant concentrations (0–5 wt.% of the solids), and shear rates (γ̇=101 to 103 s−1). The polymeric surfactant of propylene glycol facilitated the suspension flow, resulted in ∼60% reduction in viscosity (γ̇=102 s−1). A shear-thinning flow behavior was generally observed in the shear regime investigated, while dilatancy or even shear thickening was found at high shear rates (typically at γ̇>600 s−1). The shear-thinning flow revealed that the powdered suspensions were flocculated in structure. An estimate of the fractal dimension (Df) of the suspension indicated that Df=2.2 and 2.1 for the Ni suspensions with and without the polymeric surfactant, respectively. The similar Df values suggested that the suspensions structures were most likely of a reaction-limited cluster aggregation (RLCA) model; to which, particle rearrangements were expected to occur as the suspensions were under shear stresses.