Discontinuous and Dilatant Viscosity Behavior in Concentrated Suspensions. I. Observation of a Flow Instability

Abstract

The rheological dilatancy of concentrated suspensions has been studied to determine the cause of this phenomenon. If monodisperse suspensions of polymeric resins are examined, dilatant viscosity behavior is transformed into a discontinuous viscosity behavior when the volume fraction of solids is raised above 0.50. Experimental evidence is presented which supports the hypothesis that the discontinuity is caused by a flow instability in which surfaces of spheres, packed in a two dimensional hexagonal packing at low shear rates, break up into less ordered arrays of spheres. Although various techniques have been used, white light diffraction from a suspension under shear provides the most dramatic evidence of the ordered packing of the spheres and the order-disorder transition at the instability point.

Gelation, Shear-Thinning and Shear-Thickening in Cement Slurries

“…Moreover, at high enough volume fractions, the collapse of gaps between particles induces the formation of elongated clusters along the compressional axis of flow [25]. On the other hand, concentration fluctuations lead to an increase of the viscosity [26] and, eventually, to complete jamming of the suspension [27] (flow stops). One may thus assume, by similarity with dry granular materials, that clusters of some sort form force chains which are able to sustain the stress applied along the compressional direction [28].…”

Colloidal Processing of Ceramics

“…There is a need for more-sophisticated theories, as well as new characterization methods to probe local suspension structure. Scattering measurements have been an effective tool to study order-disorder 98 and particle-clustering transitions 39 in concentrated systems. However, scattering measurements assess only bulk properties.…”

Probing nonlinear rheology layer-by-layer in interfacial hydration water

“…Although shear thinning (decrease of viscosity) originates from the decrease of particle density correlation (2, 12), shear thickening (4, 7, 8, 13-17) (increase of viscosity) has been understood in various perspectives such as hydrodynamic instability (18) at high Reynolds number (Re) or order-disorder transition (13,14) at low Re and high Weissenberg number (Wi) [a measure of elasticity of viscoelastic flows (1); see SI Appendix, section S1, for nonlinear hydrodynamics formalism based on Re and Wi]. In particular, such a viscoelastic flow with low Re and high Wi exhibits behaviors similar to the inertial turbulence of Newtonian flow, so termed the elastic turbulence (4, 17).…”