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 (phi = 0.05-0.25), surfactant concentrations (0-5 wt.% of the solids), and shear rates (gamma = 10(1) to 10(3) s(-1)). The polymeric surfactant of propylene glycol facilitated the suspension flow, resulted in similar to60% reduction in viscosity (gamma = 10(2) 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 gamma > 600 s(-1)). The shear-thinning flow revealed that the powdered suspensions were flocculated in structure. An estimate of the fractal dimension (D-f) of the suspension indicated that D-f = 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. (C) 2003 Elsevier B.V. All rights reserved.