Dilatancy, jamming, and the physics of granulation

Abstract

Granulation is a process whereby a dense colloidal suspension is converted into pasty granules (surrounded by air) by application of shear. Central to the stability of the granules is the capillary force arising from the interfacial tension between solvent and air. This force appears capable of maintaining a granule in a jammed solid state, under conditions where the same amount of solvent and colloid could also exist as a flowable droplet. We argue that in the early stages of granulation the physics of dilatancy, which requires that a powder expand on shearing, is converted by capillary forces into the physics of arrest. Using a schematic model of colloidal arrest under stress, we speculate upon various jamming and granulation scenarios. Some preliminary experimental results on aspects of granulation in hard-sphere colloidal suspensions are also presented.

Shear Thickening of Cornstarch Suspensions as a Reentrant Jamming Transition

“…The latter provides a confining pressure that is mainly due to the surface tension of the solvent, making it impossible to remove grains from the suspension. As suggested by Cates et al [17], the confinement pressure associated with this should be on the order of the surface tension over the grain size, P c =R 7000 Pa, of the same order of magnitude as the typical normal stresses measured in the experiments near the onset of shear thickening. In addition, this gives a maximal dilation that is on the order of 1 particle diameter ( 20 m); compared to the radius of the plate-plate cell this gives a maximum dilation of about 0.1%, too small to be detected by our MRI density measurements.…”

Granular suspension avalanches. I. Macro-viscous behavior

“…2,3 The presence of a particle network demonstrates that granular suspensions exhibit long-range spatial ordering of their microstructure (i.e., the particle arrangement), which creates a coupling between the local behavior and bulk motion. This gives rise to a number of effects present in dry granular materials such as dilatancy, 4, 5 shear banding, 6 particle jamming, 7,8 and frictional behavior. 9,10 At the same time, the grains are saturated with viscous fluids and inherit some of the features of concentrated suspensions such as shear thickening, particle migration, and normal stress effects.…”

Volume fraction variations and dilation in colloids and granulars

“…The experiments in Cates et al (2005), Fall et al (2008) and Haw (2004), as well as a large body of rheological literature (e.g. Metzner & Whitlock 1958), demonstrate that concentrated suspensions are 'naturally' prone to respond by dilation.…”

“…on May 9, 2018 http://rsta.royalsocietypublishing.org/ Downloaded from mechanism proposed in Cates et al (2005).) However, once pore pressure is equilibrated by interstitial fluid transfer, the hardening stress returns to zero and the dilated region is no longer strengthened against shear deformation: this is when the actual earthquake shear strain occurs.…”

“…fluid interfaces (Cates et al 2005), the total volume must be conserved. Recent experiments demonstrate that rheological jamming in cornstarch suspensions (not strictly colloidal) is directly associated with global dilation (Fall et al 2008).…”