Shear thickening and jamming in densely packed suspensions of different particle shapes

Abstract

We investigated the effects of particle shape on shear thickening in densely packed suspensions. Rods of different aspect ratios and nonconvex hooked rods were fabricated. Viscosity curves and normal stresses were measured using a rheometer for a wide range of packing fractions for each shape. Suspensions of each shape exhibit qualitatively similar discontinuous shear thickening. The logarithmic slope of the stress vs shear rate increases dramatically with packing fraction and diverges at a critical packing fraction φ(c) which depends on particle shape. The packing fraction dependence of the viscosity curves for different convex shapes can be collapsed when the packing fraction is normalized by φ(c). Intriguingly, viscosity curves for nonconvex particles do not collapse on the same set as convex particles, showing strong shear thickening over a wider range of packing fraction. The value of φ(c) is found to coincide with the onset of a yield stress at the jamming transition, suggesting the jamming transition also controls shear thickening. The yield stress is found to correspond with trapped air in the suspensions, and the scale of the stress can be attributed to interfacial tension forces which dramatically increase above φ(c) due to the geometric constraints of jamming. Using this connection we show that the jamming transition can be identified by simply looking at the surface of suspensions. The relationship between shear and normal stresses is found to be linear in both the shear thickening and jammed regimes, indicating that the shear stresses come from friction. In the limit of zero shear rate, normal stresses pull the rheometer plates together due to the surface tension of the liquid below φ(c), but push the rheometer plates apart due to jamming above φ(c).

Red cells’ dynamic morphologies govern blood shear thinning under microcirculatory flow conditions

“…Both suspensions of HRBCs show a nearly Newtonian behavior except for shear rates above 400 s −1 , where the onset of a slight shear-thickening is observed especially for hardened discocytes. This behavior is similar to shear thickening reported for rigid colloidal suspensions (22,23). For both HRBC dispersions viscosity values are larger than those for washed blood; however, the sample with hardened polylobes yields a 70% lower relative viscosity than that for stiffened discocytes, as seen in Fig.…”

Rheology of concentrated suspensions of non-colloidal rigid fibres

“…Hence, we argue that the aspect ratio principally affects the maximum volume fraction at which the suspensions can be sheared. A similar collapse of the rheological data across multiple aspect ratios has been observed previously for shear-thickening suspensions of colloidal fibres (Brown et al 2011).…”

“…Likewise, the volume fraction at which the shear stresses diverge, and the flow of the suspension ceases (i.e. becomes jammed), has not been determined previously for non-colloidal fibres, though such measurements have been made for shear-thickening suspensions of colloidal fibres (Egres & Wagner 2005;Brown et al 2011).…”

Gas migration regimes and outgassing in particle-rich suspensions

“…These dense suspensions dilate in response to shear, and can therefore develop a normal force against their boundaries and build force-bearing networks of particles. The strength of the particle networks is determined by the number of particles in contact with each other [22], the friction between particles [36], and the magnitude of the forces that resist particle displacement / dilation, such as the flexibility of the boundaries against which the force chains rest [24,37], or the applied pressure [e.g., from gravitational loading; 17].…”

“…Again, confining stress matters: if the boundaries can deform freely, then the particles at the edge will intrude the surface without transmitting stress to their neighbors. However, even a small resistance from the boundary will allow stress build-up in the particle network, which can then resist shear [24]. At the random close packing, the percentage of particles in contact with each other is at its highest (for a randomly packed suspension), and even suspensions of frictionless particles develop a yield strength [21,25,26].…”