Abstract
Colloidal aggregates in a suspension of carbon black particles are characterized by fractal dimension and their shear dependence. Carbon black particles of 100 nm in diameter are dispersed in Newtonian ethylene glycol with particle volume fraction ϕ ranging from 0.01 to 0.1. Microstructure of the aggregates is estimated by hydrodynamic transport properties such as average settling velocity and shear viscosity. Scaling analysis is conducted to correlate the hydrodynamic transport properties and the fractal dimension d f . The fractal dimension is estimated to be 2.21 from the scaling relation between the settling velocity and the particle volume fraction for ϕ = 0.01-0.05. The shear viscosity results show shear-thinning behavior of the colloidal suspension. The intrinsic viscosity for the colloidal aggregates is obtained from the data of shear viscosity versus particle concentration. A scaling relation between the intrinsic viscosity and the shear rate gives d f = 1.93 at m = 1/3, where m is the exponent defined by a scaling relation between aggregate radius R g and shear rate S, R g ∝S −m. Another scaling relation using yield stress data presents d f = 1.94, which is nearly equivalent to 1.93 from that by the intrinsic viscosity but quite lower than that from the settling velocity. This discrepancy of the fractal dimension can be attributed to growth or restructuring of the colloidal aggregates by the hydrodynamic stress during long-time settling process.
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Lee, H., Koo, S. Analysis of fractal aggregates in a colloidal suspension of carbon black from its sedimentation and viscosity behavior. Korea-Aust. Rheol. J. 28, 267–273 (2016). https://doi.org/10.1007/s13367-016-0028-1
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DOI: https://doi.org/10.1007/s13367-016-0028-1