Localized stress fluctuations drive shear thickening in dense suspensions

Dense particulate suspensions exhibit a dramatic increase in average viscosity above a critical, material-dependent shear stress. This thickening changes from continuous to discontinuous as the concentration is increased. Using direct measurements of spatially resolved surface stresses in the contin...

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Bibliographic Details
Published inProceedings of the National Academy of Sciences - PNAS Vol. 114; no. 33; pp. 8740 - 8745
Main Authors Rathee, Vikram, Blair, Daniel L., Urbach, Jeffrey S.
Format Journal Article
LanguageEnglish
Published United States National Academy of Sciences 15.08.2017
Subjects
Mechanical stimuli
Physical Sciences
Rheology
Shear rate
Shear stress
Shear thickening (liquids)
Shearing
Thickening
Viscosity
shear thickening
colloids
rheology
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Summary:Dense particulate suspensions exhibit a dramatic increase in average viscosity above a critical, material-dependent shear stress. This thickening changes from continuous to discontinuous as the concentration is increased. Using direct measurements of spatially resolved surface stresses in the continuous thickening regime, we report the existence of clearly defined dynamic localized regions of substantially increased stress that appear intermittently at stresses above the critical stress. With increasing applied stress, these regions occupy an increasing fraction of the system, and the increase accounts quantitatively for the observed shear thickening. The regions represent high-viscosity fluid phases, with a size determined by the distance between the shearing surfaces and a viscosity that is nearly independent of shear rate but that increases rapidly with concentration. Thus, we find that continuous shear thickening arises from increasingly frequent localized discontinuous transitions between distinct fluid phases with widely differing viscosities.
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Author contributions: V.R., D.L.B., and J.S.U. designed research; V.R. performed research; V.R., D.L.B., and J.S.U. analyzed data; and V.R., D.L.B., and J.S.U. wrote the paper.
Edited by Morton M. Denn, The City College of New York, New York, NY, and accepted by Editorial Board Member Herbert Levine June 28, 2017 (received for review March 8, 2017)
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.1703871114