New insights on carbon black suspension rheology—Anisotropic thixotropy and antithixotropy

We report a detailed experimental study of peculiar thixotropic dynamics carbon black (CB, Vulcan XC-72) suspensions in mineral oil, specifically the observation sequential stress increase then decrease at fixed shear rate step-down test. verify that such dynamics, though peculiar, come from true material response rather than artifacts. also reveal how this long-time decay is associated with anti-thixotropy, viscoelasticity, by using orthogonal superposition (OSP) rheometry to probe viscoelastic moduli during tests. The storage and loss modulus are present, showing two-timescale recovery response, which demonstrates anti-thixotropic, it involves shear-induced structuring. further show mechanical anisotropy CB suspension under OSP. Based on rheological results, microstructural schematic proposed, considering qualitatively structure build-up, anti-thixotropic densification, anisotropic evolution. Our for these outside standard paradigm structure-parameter models, elastic provides us new insight into transient suspensions.