A New Application for Brookfield Viscometers: Viscoelastic Property Determination
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Date
2006-07-29
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Abstract
Viscoelastic properties are traditionally measured using sophisticated and expensive instruments. Brookfield YR-I is an affordable instrument, primarily developed to measure the yield stress of materials with a vane attachment. In recent years, vane attachments have gained popularity from various advantages, including elimination of wall slip, minimum disturbance to sample, quick single point determination, and easy fabrication and cleaning. Prior research has established that the vane can be used to measure elastic shear moduli of materials. This research project attempts to apply the Brookfield YR-I rheometer to the measurement of viscoelastic properties. Different concentrations of gelatin and polyacrylamide gels served as model systems for viscoelastic and elastic materials, respectively. The concepts developed were applied to the torque-time response obtained for these model systems from the Brookfield YR-I. The data compared favorably with viscoelastic data obtained from oscillatory testing with a stress controlled rheometer. The results helped establish a protocol for the Brookfield YR-I to measure viscoelastic properties. Furthermore, certain commercial products were tested using the protocol, but disagreement between the machines was observed in some materials. The effect of cup size and the position of the assumed Newtonian line are potential reasons for the disparity, and future work should focus on refining these aspects.
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Keywords
viscoelasticity, yield stress, rheology, vane
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Degree
MS
Discipline
Biological and Agricultural Engineering
