1 Distinguishing Thixotropy from Viscoelasticity Mayank Agarwal, a Shweta Sharma, a V. Shankar*, Yogesh M. Joshi* Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016. INDIA. * Corresponding authors, email id: [email protected] and [email protected] a Both authors contributed equally to this manuscript. Abstract: Owing to non-linear viscoelasticity, materials often show characteristic features that resemble those of thixotropy. This issue has been debated in the literature over the past several decades, and several experimental protocols have been proposed to distinguish thixotropy from viscoelasticity. In this work, we assess these protocols by carrying out experiments using polymer solutions, thixotropic clay dispersions and modelling their behavior respectively using the FENE- P constitutive equation and a viscoelastic aging model. We find that the criteria proposed in the literature, such as a step-down jump in shear rate and shear start-up at different waiting times elapsed since pre-shear, are inadequate to distinguish thixotropy from viscoelasticity. In marked contrast, we show that the application of step-strain or step-stress after cessation of pre-shear serves as a useful discriminant between thixotropy and viscoelasticity. In thixotropic materials, we observe that the application of step strain (or step stress) after cessation of pre-shear eventually leads to slowing down of relaxation dynamics as a function of waiting time. However, for viscoelastic materials, the relaxation modulus (creep compliance) curve shifts to lower modulus (higher compliance) values as a function of waiting time until equilibrium is reached. While the proposed criterion offers a robust distinction between viscoelasticity and thixotropy for the systems studied here, further experimental investigations based on other systems are needed to establish its versatility and will lead to a greater insight into this long-standing issue in rheological categorization. This is the author’s peer reviewed, accepted manuscript. However, the online version of record will be different from this version once it has been copyedited and typeset. PLEASE CITE THIS ARTICLE AS DOI: 10.1122/8.0000262
Distinguishing Thixotropy from Viscoelasticity
Jun 18, 2023
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