Yield stress measurement of a thixotropic colloid

Yield stress measurements have long been considered to be inconsistent and difficult, especially for a thixotropic colloid, since the thixotropic behavior gives rise to time-dependent rheological properties. In this paper, we attempted measuring the yield stress of aqueous xanthan gum (XG) solutions...

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Bibliographic Details
Published in:Rheologica acta 2019-07, Vol.58 (6-7), p.383-401
Main Authors: Ong, Ernest E. S., O’Byrne, Sean, Liow, Jong Leng
Format: Article
Language:English
Subjects:
Aqueous solutions
Avalanches
Characterization and Evaluation of Materials
Chemistry and Materials Science
Complex Fluids and Microfluidics
Creep tests
Food Science
Gels
Materials Science
Measurement methods
Mechanical Engineering
Original Contribution
Polymer Sciences
Relaxation time
Rheological properties
Rheology
Shear strength
Soft and Granular Matter
Storage modulus
Stress measurement
Stress relaxation
Time dependence
Wall slip
Xanthan
Yield strength
Yield stress
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Summary:Yield stress measurements have long been considered to be inconsistent and difficult, especially for a thixotropic colloid, since the thixotropic behavior gives rise to time-dependent rheological properties. In this paper, we attempted measuring the yield stress of aqueous xanthan gum (XG) solutions in different XG concentration. Our rheological measurements showed that XG in aqueous solutions, which can be characterized as weak gels, were thixotropic for 0.4, 0.6, 0.8, and 1 wt% XG concentrations. To ensure the accuracy of our rheological measurement data, detailed wall slip and stress relaxation time were first investigated prior to the actual yield stress measurement. A standard sample loading procedure was used to ensure the consistency of the loaded sample. Various methods were employed such as steady shear, oscillatory shear, rheological model fitting, and creep test to determine the yield stress of aqueous XG solutions. A sigmoidal model was also proposed to obtain a yield stress from our steady shear measurement unambiguously. In our steady shear measurements, a resistance to an avalanche of flow is observed and it is likely due to a conformational change of XG polymers under shear. As compared to other measurement methods, it was found that the most reliable way to obtain a yield stress is via small amplitude oscillatory shear measurements, in which a yield stress can be obtained conveniently at the maximum storage modulus, and it is well matched with our steady shear and creep test results.
ISSN:0035-4511
1435-1528
DOI:10.1007/s00397-019-01154-y