3 research outputs found
Glass transitions and shear thickening suspension rheology
We introduce a class of simple models for shear thickening and/ or `jamming'
in colloidal suspensions. These are based on schematic mode coupling theory
(MCT) of the glass transition, having a memory term that depends on a density
variable, and on both the shear stress and the shear rate. (Tensorial aspects
of the rheology, such as normal stresses, are ignored for simplicity.) We
calculate steady-state flow curves and correlation functions. Depending on
model parameters, we find a range of rheological behaviours, including
`S-shaped' flow curves, indicating discontinuous shear thickening, and
stress-induced transitions from a fluid to a nonergodic (jammed) state, showing
zero flow rate in an interval of applied stress. The shear thickening and
jamming scenarios that we explore appear broadly consistent with experiments on
dense colloids close to the glass transition, despite the fact that we ignore
hydrodynamic interactions. In particular, the jamming transition we propose is
conceptually quite different from various hydrodynamic mechanisms of shear
thickening in the literature, although the latter might remain pertinent at
lower colloid densities. Our jammed state is a stress-induced glass, but its
nonergodicity transitions have an analytical structure distinct from that of
the conventional MCT glass transition.Comment: 33 pages; 19 figure
Dilatancy, Jamming, and the Physics of Granulation
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
solvent 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
reported.Comment: Original article intended for J Phys Cond Mat special issue on
Granular Materials (M Nicodemi, Ed.