Generality of shear thickening in dense suspensions

Abstract

Suspensions are of wide interest and form the basis for many smart fluids [1][2][3][4][5][6][7]. For most suspensions, the viscosity decreases with increasing shear rate, i.e. they shear thin. Few are reported to do the opposite, i.e. shear thicken, despite the longstanding expectation that shear thickening is a generic type of suspension behavior [8, 9]. Here we resolve this apparent contradiction. We demonstrate that shear thickening can be masked by a yield stress and can be recovered when the yield stress is decreased below a threshold. We show the generality of this argument and quantify the threshold in rheology experiments where we control yield stresses arising from a variety of sources, such as attractions from particle surface interactions, induced dipoles from applied electric and magnetic fields, as well as confinement of hard particles at high packing fractions. These findings open up possibilities for the design of smart suspensions that combine shear thickening with electro-or magnetorheological response.Shear thickening is presumed to be due to general mechanisms such as hydrodynamics [9, 10] or dilation [11][12][13], and thus all suspensions are expected to exhibit shear thickening under the right conditions [8]. So far, however, the exact conditions have not been determined. One condition is apparently set by attractive particle interactions. It has long been known that attractions, observed as flocculation in suspensions, can prevent shear thickening. This has been shown by modifying the chemistry, for example by adding flocculating agents to observe the transition from shear thickening to thinning (for a review, see [8]). In other cases, crossing the gel transition was shown to eliminate shear thickening [14,15]. A key problem, therefore, is to understand how interparticle attractions interfere with shear thickening. We demonstrate here that a simple and direct criterion for the existence of an observable shear thickening regime in dense, non-Brownian suspensions can be developed by comparing the yield stress produced by attractions with the inherent shear thickening stresses. We then generalize this condition to show how a yield stress from any source modifies the shear thickening phase diagram.Our experiments used an Anton Paar rheometer to * Electronic address: embrown@uchicago.edu •: viscosity curve of the same system at the same φ with added surfactant. The shear thickening regime is the region of positive slope in the curves of viscosity η versus applied stress τ . Shear thinning is characterized by a negative slope and Newtonian fluids, such as water, exhibit constant η. b, Images show clustering due to interparticle attractions (top) and no clustering when surfactant is added (bottom). Scale bar is 200 µm. All images (including subsequent figures) were taken at rest under an optical microscope in a dilute quasi two-dimensional layer. In this dilute case, attractions can be observed by the high number of particle contacts in the form of clusters or chains.measure the shear stress τ an...

Does Shear Thickening Occur in Semisolid Metals?

“…This analysis can rationalize the apparently contradictory results from Kumar et al, [23,27] Peng and Wang, [26] Koke and Modigell [25] , and Liu et al [24] The reanalysis shows that Liu et al [24] do have results (for a fraction solid of 0.5) which display shear thickening but only when the shear rate jump is occurring from a finite shear rate. If it takes place from rest then the yield stress masks any underlying behavior as discussed by Brown et al [6] where it is argued that yield can mask shear thickening. For the jumps from a finite shear rate for fractions solid of greater than about 0.36, an instantaneous shear thickening response is occurring (even if the steady-state behavior is shear thinning) almost certainly for the reasons identified by Brown and Jaeger [12] i.e., the confining stress at boundaries frustrating dilatation.…”

“…This is the phenomenon observed with dense suspensions of cornstarch in water, which allows someone to run across the surface of the suspension in a swimming bath for example (but when they stand still they sink in). Brown et al [6] have argued that all suspensions should show shear thickening under certain conditions because the underlying mechanisms (hydrodynamics, [7,8] dilatation [9][10][11] ) are general but they demonstrate that shear thickening can be masked by a yield stress. They attribute discontinuous shear thickening to frictional particle contacts that form when dense particle arrangements begin to dilate and push against boundaries.…”

“…(1) Differences in the shear rate ranges and fractions solid considered; (2) Whether inertia (both of the measuring head and of the semisolid fluid itself) has been appropriately considered; (3) The size of the particles in relation to the size of the gap between the inner bob and outer cup of the rheometer; (4) The existence of a yield stress masking the shear thickening phenomenon as argued by Brown et al [6] B. Shear Rate Range and Fraction Solid…”

“…The longer the rest period in the semisolid state prior to semisolid processing, the greater the resistance to deagglomeration in the initial stages of flow. Brown et al [6] have argued that yield masks shear thickening. This is consistent with the argument in Alexandrou et al [18,19] about the existence of a yielded zone for low shear rates.…”

Design and Manufacturing of a Novel Shear Thickening Fluid Composite (STFC) with Enhanced out-of-Plane Properties and Damage Suppression

“…To achieve this, the continuous phase must induce steric or electrosteric stabilisation in order to enhance the colloid stability. Several carriers can be used for the preparation of the STF, such as ethylene glycol [15,16], water [17] and other organic solvents, however the most used one for structural application is polyethylene glycol due to its tendency to form very stable suspension [4,18] coupled with its biocompatibility.…”