70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017;
Denver, Colorado
Session J39: Shear Thickening in Suspensions: The Lubricated-to-Frictional Contact Scenario
2:45 PM–3:20 PM,
Monday, November 20, 2017
Room: Four Seasons Ballroom 1-3
Chair: Martin Maxey, Brown University
Abstract ID: BAPS.2017.DFD.J39.1
Abstract: J39.00001 : Shear thickening in suspensions: the lubricated-to-frictional contact scenario*
2:45 PM–3:20 PM
Preview Abstract
Author:
Jeffrey Morris
(Levich Institute, CUNY City College of New York)
Suspensions of solid particles in viscous liquids can vary from low-viscosity liquids to wet granular materials or soft solids depending on the
solids loading and the forces acting between particles.
When the particles are very concentrated, these mixtures are "dense suspensions." Dense suspensions often exhibit shear thickening, an increase in
apparent viscosity as the shear rate is increased. In its most extreme form, order of magnitude increases in viscosity
over such a narrow range in shear rate occur that the term discontinuous shear thickening (DST) is applied.
DST is particularly striking as it occurs in the relatively simple case of nearly hard spheres in a Newtonian liquid, and is found to take place for
submicron particles in colloidal dispersions to much larger particle corn starch dispersions.
We focus on simulations of a recently developed ``lubricated-to-frictional" rheology in which the interplay of viscous lubrication, repulsive surface forces, and contact friction between particle surfaces provides a scenario to explain DST. Our simulation method brings together elements of the discrete-element method from granular flow with a simplified
Stokesian Dynamics, and can rationalize not only the abrupt change in properties with imposed shear rate (or shear stress), but also the magnitude of the change. The large change in properties is associated with the breakdown of lubricating films between particles, with activation of Coulomb friction between particles. The rate dependence is caused by the shearing forces driving particles to
contact, overwhelming conservative repulsive forces between surfaces; the repulsive forces are representative of colloidal stabilization by surface charge or steric effects, e.g. due to adsorbed polymer.
The results of simulation are compared to developments by other groups, including a number of experimental studies and a theory incorporating the same basic elements as
the simulation.
The comparison to experiments of the predictions of the lubricated-to-frictional rheology is generally good, but discrepancies demand
some perspective on the strong simplifying assumptions in the model. Since contact is difficult to both establish and to characterize for surfaces between particles of micron scale or smaller, what is happening in the very close ``contacts" is not clear, and how changes at this scale give rise to the large-scale force organization is yet to be established.
The insight to the elements needed for the abrupt flow induced transition seen in DST thus suggests a need for consideration of both the microscopic physics of contact and the statistical
physics governing the macroscopic properties.
*This work was supported in part by the NSF CBET program, grant # 1605283.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2017.DFD.J39.1