Mircorheology and jamming in a yield-stress fluid |
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Authors: | F K Oppong J R de Bruyn |
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Institution: | (1) Department of Physics and Astronomy, University of Western Ontario, London, ON, Canada, N6A 3K7;(2) Unilever Research and Development, Colworth Science Park Sharnbrook, Bedfordshire, MK44 1LQ, UK; |
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Abstract: | We study the onset of a yield stress in a polymer microgel dispersion using a combination of particle-tracking microrheology
and shear rheometry. On the bulk scale, the dispersion changes from a predominantly viscous fluid to a stiff elastic gel as
the concentration of the microgel particles increases. On the microscopic scale, the tracer particles see two distinct microrheological
environments over a range of concentrations—one being primarily viscous, the other primarily elastic. The fraction of the
material that is elastic on the microscale increases from zero to one as the concentration increases. Our results indicate
that the yield stress appears as the result of jamming of the microgel particles, and we infer a model for the small-scale
structure and interactions within the dispersion and their relationship to the bulk viscoelastic properties. |
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