Dilatancy in the flow and fracture of stretched colloidal suspensions

Abstract

Concentrated particulate suspensions, commonplace in the pharmaceutical, cosmetic and food industries, display intriguing rheology. In particular, the dramatic increase in viscosity with strain rate (shear thickening and jamming), which is often observed at high-volume fractions, is of practical and fundamental importance. Yet, manufacture of these products and their subsequent dispensing often involves flow geometries substantially different from that of simple shear flow experiments. In this study, we show that the elongation and breakage of a filament of a colloidal fluid under tensile loading is closely related to the jamming transition seen in its shear rheology. However, the modified flow geometry reveals important additional effects. using a model system with nearly hard-core interactions, we provide evidence of surprisingly strong viscoelasticity in such a colloidal fluid under tension. With high-speed photography, we also directly observe dilatancy and granulation effects, which lead to fracture above a critical elongation rate.

Drop formation in shear-thickening granular suspensions

“…It was argued in [11] that the force balance takes place more locally here and that the capillary pressure exerted at the level of the individual particles protruding from the interface is balanced by the fluid inertia. Exponential thinning is also observed in colloidal and cornstarch suspensions: the thinning dynamics proceeds more slowly than that in the Newtonian case and the thinning neck becomes cylindrical [12,13]. The overall picture is still not clear and the different mechanisms at play deserve further systematic study.…”

“…On the other hand, drop formation in non-Newtonian fluids, which is important in areas such as emulsification, inkjet printing, and agricultural spraying, is still ill understood in many cases [1][2][3][4] and continues to attract considerable attention [5][6][7][8][9][10][11][12][13]. For instance, theoretical analysis predicts that the drop breakup in shear thinning fluids proceeds faster than that in the Newtonian case due to the high elongational rates present in the fluid neck during the thinning [14,15].…”

“…Recent studies show that during breakup different scenarios may occur [22]; the breakup may be viscocapillary but governed by either the solvent or the suspension viscosity [8][9][10]. Also new regimes are found that are dramatically different from the predictions for simple fluids [11][12][13].…”

Capillary breakup of suspensions near pinch-off

“…Dispersions that exhibit shear-thickening can show viscoelastic pinch-off or dilatancy effects depending on the strain rate 23,24 . However, other non-Brownian suspensions display a faster thinning rate close to pinch-off than that predicted by the viscous scaling law for the bulk viscosity [25][26][27][28][29][30] .…”

Complex Fluids in Energy Dissipating Systems

“…This rheological information is insufficient to predict the flow behavior under complex dynamics and that may be the reason behind the lack of constitutive models for STFs beyond ad-hoc Generalized Newtonian Fluid models [125][126][127]. Since the beginning of XXI Century, the amount of studies dealing with the dynamic, transient and the extensional rheology of STFs has risen considerably [128][129][130][131][132][133][134][135][136][137][138][139][140], coinciding with the eclosion of industrial applications of STFs. In many of these applications [141], STF is used in combination with a flexible porous material, i.e., fabrics, open-cell foams, etc., either by coating or impregnating it [142,143]; in other applications, the shear thickening fluid is held between plates in a sandwich structure or in reservoirs.…”