CiteULike: dchen Ovarlez

Flow of Wet Granular Materials

N Huang — 2008-06-22T00:55:36-00:00

Physical Review Letters, Vol. 94, No. 2. (2005)

The transition from frictional to lubricated flows of a dense suspension of non-Brownian particles is studied. The pertinent parameter characterizing this transition is the Leighton number Le = , the ratio of lubrication to frictional forces. Le defines a critical shear rate below which no steady flow without localization exists. In the frictional regime the shear flow is localized. The lubricated regime is not simply viscous: the ratio of shear to normal stresses remains constant and the velocity profile has a universal form in both frictional and lubricated regimes. Finally, a discrepancy between local and global measurements of viscosity is identified, which suggests inhomogeneity of the material under flow.

Physical age of soft-jammed systems

G Ovarlez — 2008-06-10T23:51:18-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 76, No. 1. (2007)

We study experimentally the liquid-solid transition in a soft-jammed system and focus on its aging in the solid regime. We investigate the impact of temperature, density, and load changes on the material behavior. We show that all elastic modulus versus time curves fall on a single master curve when rescaled by an appropriate factor function of the density, the temperature, the load, and the time elapsed since preshear. This allows us to distinguish the effect of temperature and density on the mechanical properties and their effect on aging. Since the time evolutions of the elastic modulus under various conditions are similar within a factor, we suggest that the rescaled time reflects the physical age of the material; i.e., it describes the degree of progress of the structural organization relative to a state of reference of the system in the solid regime and constitutes a means for characterizing the effective state of such systems.

Transition from a simple yield-stress fluid to a thixotropic material

A Ragouilliaux — 2008-06-10T16:55:47-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 76, No. 5. (2007)

From magnetic resonance imaging rheometry we show that a pure emulsion can be turned from a simple yield stress fluid to a thixotropic material by adding a small fraction of colloidal particles. The two fluids have the same behavior in the liquid regime but the loaded emulsion exhibits a critical shear rate below which no steady flows can be observed. For a stress below the yield stress, the pure emulsion abruptly stops flowing, whereas the viscosity of the loaded emulsion continuously increases in time, which leads to an apparent flow stoppage. This phenomenon can be very well represented by a model assuming a progressive increase of the number of droplet links via colloidal particles.

Shear Thickening of Cornstarch Suspensions as a Reentrant Jamming Transition

Abdoulaye Fall — 2008-03-18T01:32:20-00:00

Physical Review Letters, Vol. 100, No. 1. (2008)

We study the rheology of cornstarch suspensions, a non-Brownian particle system that exhibits shear thickening. From magnetic resonance imaging velocimetry and classical rheology it follows that as a function of the applied stress the suspension is first solid (yield stress), then liquid, and then solid again when it shear thickens. For the onset of thickening we find that the smaller the gap of the shear cell, the lower the shear rate at which thickening occurs. Shear thickening can then be interpreted as the consequence of dilatancy: the system under flow wants to dilate but instead undergoes a jamming transition because it is confined, as confirmed by measurement of the dilation of the suspension as a function of the shear rate.