Abstract
Dilute oil dispersions of fractal carbon black particles with attractive van der Waals interactions display continuous shear thickening followed by shear thinning at high shear rates. The shear thickening transition occurs at gamma c approximately 10(2)-10(3) s(-1) and is driven by hydrodynamic breakup of clusters. Pre-shearing dispersions at shear rates gamma>gamma c produces enhanced-modulus gels where G' approximately sigma pre-shear 1.5-2 and is directly proportional to the residual stress in the gel measured at a fixed sample age. The observed data can be accounted for using a simple scaling model for the breakup of fractal clusters under shear stress.
Highlights
Dilute oil dispersions of fractal carbon black particles with attractive van der Waals interactions display continuous shear thickening followed by shear thinning at high shear rates
The shear thickening transition occurs at ␥ ̇ c Ϸ 102 − 103 s−1 and is driven by hydrodynamic breakup of clusters
Pre-shearing dispersions at shear rates ␥ ̇ Ͼ ␥ ̇ c produces enhanced-modulus gels where GЈ ϳ 1p.r5e−-s2hear and is directly proportional to the residual stress in the gel measured at a fixed sample age
Summary
We find the elasticity of gels formed by pre-shearing above the shear thickening transition scales as a power law with the pre-shear stress, and is directly proportional to the internal stress in the sample, which we measure. We propose a scaling model which considers the dependence of the gel modulus on the cluster number density produced during pre-shear flow.
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