New insights on carbon black suspension rheology—Anisotropic thixotropy and antithixotropy
New insights on carbon black suspension rheology—Anisotropic thixotropy and antithixotropy
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炭黑悬浮液流变学新见解——各向异性触变性和抗触变性
DOI：
10.1122/8.0000455
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发表时间：
2022
影响因子：
3.3
通讯作者：
R. Ewoldt
中科院分区：
文献类型：
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作者：
Yilin Wang;R. Ewoldt
本文报道了炭黑（CB, Vulcan XC-72）悬浮液在矿物油中特有的触变动力学的详细实验研究，特别是在降压试验中观察到在固定剪切速率下应力的顺序增加和减少。我们证实，这种动力学，虽然奇特，来自一个真正的材料响应，而不是实验的人工制品。我们还揭示了这种长时间的应力衰减与抗触变结构变化有关，而不是粘弹性应力松弛，通过使用正交叠加（OSP）流变法在降压测试中探测粘弹性模量。正交存储模量和损耗模量存在，显示出这种双时间尺度的恢复然后衰减响应，这表明这种响应是抗触变的，它涉及剪切诱导的结构。我们进一步用OSP证明了剪切作用下CB悬浮液的力学各向异性。基于流变学结果，提出了定性地考虑触变结构形成、反触变致密化和各向异性结构演变的微观结构示意图。我们对这些CB悬架的观察是在触变结构参数模型的标准范式之外，弹性响应为我们提供了对CB悬架瞬态动力学的新见解。
We report a detailed experimental study of peculiar thixotropic dynamics of carbon black (CB, Vulcan XC-72) suspensions in mineral oil, specifically the observation of sequential stress increase then decrease at a fixed shear rate in a step-down test. We verify that such dynamics, though peculiar, come from a true material response rather than experimental artifacts. We also reveal how this long-time stress decay is associated with antithixotropic structural change rather than viscoelastic stress relaxation by using orthogonal superposition (OSP) rheometry to probe viscoelastic moduli during the step-down tests. The orthogonal storage and loss moduli are present, showing this two-timescale recovery then decay response, which demonstrates that this response is antithixotropic, and it involves shear-induced structuring. We further show a mechanical anisotropy in the CB suspension under shear using OSP. Based on the rheological results, a microstructural schematic is proposed, considering qualitatively thixotropic structure build-up, antithixotropic densification, and anisotropic structure evolution. Our observation for these CB suspensions is outside the standard paradigm of thixotropic structure-parameter models, and the elastic response provides us with new insight into the transient dynamics of CB suspensions.