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Abstract: We investigate confined shear thickening suspensions for which the samplethickness is comparable to the particle dimensions. Rheometry measurements arepresented for densely packed suspensions of spheres and rods with aspect ratios6 and 9. By varying the suspension thickness in the direction of the sheargradient at constant shear rate, we find pronounced oscillations in the stress.These oscillations become stronger as the gap size is decreased, and the stressis minimized when the sample thickness becomes commensurate with an integernumber of particle layers. Despite this confinement-induced effect, viscositycurves show shear thickening that retains bulk behavior down to samples as thinas two particle diameters for spheres, below which the suspension is jammed.Rods exhibit similar behavior commensurate with the particle width, but theyshow additional effects when the thickness is reduced below about a particlelength as they are forced to align; the stress increases for decreasing gapsize at fixed shear rate while the shear thickening regime graduallytransitions to a Newtonian scaling regime. This weakening of shear thickeningas an ordered configuration is approached contrasts with the strengthening ofshear thickening when the packing fraction is increased in the disordered bulklimit, despite the fact that both types of confinement eventually lead tojamming.



Autor: Eric Brown, Hanjun Zhang, Nicole A. Forman, Benjamin W. Maynor, Douglas E. Betts, Joseph M. DeSimone, Heinrich M. Jaeger

Fuente: https://arxiv.org/



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