Contact Networks Enhance Shear Thickening in Attractive Colloid-Polymer Mixtures

Increased shear thinning arising due to strong attractive interactions between colloidal particles is thought to obscure shear thickening. Here, we demonstrate how moderate attractions, induced by adding a nonadsorbing polymer, can instead enhance shear thickening. We measure the rheology of colloid...

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Bibliographic Details
Published in:Physical review letters 2019-06, Vol.122 (22), p.228003-228003, Article 228003
Main Authors: Park, Nayoung, Rathee, Vikram, Blair, Daniel L, Conrad, Jacinta C
Format: Article
Language:English
Subjects:
Colloids
Polymers
Rheological properties
Rheology
Shear stress
Shear thickening (liquids)
Shear thinning (liquids)
Thickening
Variations
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Summary:Increased shear thinning arising due to strong attractive interactions between colloidal particles is thought to obscure shear thickening. Here, we demonstrate how moderate attractions, induced by adding a nonadsorbing polymer, can instead enhance shear thickening. We measure the rheology of colloidal suspensions at a constant particle volume fraction of ϕ=0.40 with dilute to weakly semidilute concentrations of three polyacrylamide depletants of different molecular weights. Suspensions containing large polymer exhibit increased shear thickening and positive first normal stress differences at high shear stress, and increased heterogeneous fluctuations in the boundary stress. These results are consistent with a friction-based model for shear thickening, suggesting that the presence of large, extended polymers induces the formation of near-spanning networks of interparticle contacts.
ISSN:0031-9007
1079-7114
DOI:10.1103/PhysRevLett.122.228003