Revealing the frictional transition in shear-thickening suspensions

Abstract

Shear thickening in dense particulate suspensions was recently proposed to be driven by the activation of friction above an onset stress needed to overcome repulsive forces between particles. Testing this scenario represents a major challenge because classical rheological approaches do not provide access to the frictional properties of suspensions. Here we adopt a different strategy inspired by pressure-imposed configurations in granular flows that specifically gives access to this information. By investigating the quasi-static avalanche angle, compaction, and dilatancy effects in different nonbuoyant suspensions flowing under gravity, we demonstrate that particles in shear-thickening suspensions are frictionless under low confining pressure. Moreover, we show that tuning the range of the repulsive force below the particle roughness suppresses the frictionless state and also the shearthickening behavior of the suspension. These results, which link microscopic contact physics to the suspension macroscopic rheology, provide direct evidence that the recent frictional transition scenario applies in real suspensions.soft matter | shear thickening | dense suspensions | friction D iscontinuous shear thickening occurs in suspensions whose viscosity dramatically increases, sometimes by several orders of magnitude, when the imposed shear rate exceeds a critical value (1). The archetype of such suspensions is cornstarch immersed in water. When sheared vigorously or under impact, these fluids suddenly turn into solids (2). Such remarkable properties play a key role in the flowing behavior of modern concrete (3) and have motivated applications ranging from soft-body protections to sports equipment (4). They also offer promising perspectives for the design of smart fluids with tunable rheology (5). However, the potential realm of development and applications remains largely underexplored due to the lack of understanding of this transition (6).This situation has improved very recently due to new theoretical and numerical works (7,8). Because non-Brownian suspensions of hard frictional particles immersed in a viscous fluid are Newtonian, as imposed by dimensional analysis (8-10), the key idea of these studies is to add a short-range repulsive force between particles in addition to hydrodynamics and contact forces. This repulsive force can, for instance, stem from electrostatic charges or from a specific coating of polymers on the surface of the particle (11). At small shear rate (or small stress), the repulsive force prevents the grains from coming into contact; the suspension thus flows easily as if particles were frictionless. In the remainder of this paper, this state is referred to as frictionless. The viscosity of such a frictionless suspension would diverge at random close packing, whose volume fraction is φrcp = 0.64 for monodisperse spheres. Conversely, at large shear rate (or large stress), the repulsive force is overcome by the hydrodynamic forces and particles are therefore pressed into frictional contacts. The visco...

On the kinematics and dynamics of crystal‐rich systems

“…This jamming at lower values of ϕ in frictional systems is the result of the breakdown of lubrication and the onset of frictional contacts with the appearance of force chains as described in section 3.1 [Fernandez et al, 2013;Ness and Sun, 2016b;Wyart and Cates, 2014]. It is now understood that this process is fundamental to the rheology of hydrogranular flow and signals the onset of the so-called "boundary lubrication" frictional regime distinct from the "hydrodynamic" regime, where lubrication films are intact and particle friction plays almost no role [Bi et al, 2011;Clavaud et al, 2017;Fernandez et al, 2013;Grob et al, 2014;Mari et al, 2014]. A hydrogranular system in the hydrodynamic regime will jam at a value of ϕ = ϕ RCP , like that of frictionless systems.…”

“…At large values of s, the so-called hydrodynamic regime, a fluid layer separates the two particle surfaces and so the bulk coefficient of friction depends on the value of s, not just the dry value of the particle-particle friction coefficient. However, when s ≪ 1, the system is in a contact frictional regime, the first normal stress difference is nonzero, and the bulk friction depends weakly on s and is described by the dry friction coefficient [Clavaud et al, 2017;Fernandez et al, 2013]. For geological applications we consider a roughness scale of δ rough = 1 μm.…”

“…The Sommerfeld number (39) provides the criteria for this transition between boundary and hydrodynamic states of lubrication and explains why there are two states of jamming possible in a hydrogranular systems: (1) In the hydrodynamic lubrication case, jamming occurs closer to a single value of ϕ and is not sensitive to values of particle friction coefficient, and (2) a so-called shear-jamming regime, associated with the onset of frictional contacts, the emergence of a force chain network, and a value of ϕ pc that is not single-valued and depends explicitly on the value of the particle-particle friction coefficient. The emergence of frictional behavior is now understood as contributing to continuous (suspension viscosity is proportional to shear rate) and producing discontinuous (large discontinuous jumps in suspension viscosity as a function of shear rate) shear thickening as well [Clavaud et al, 2017;Lin et al, 2015;Majumdar et al, 2017;Mari et al, 2014;Ness and Sun, 2015, 2016a, 2016bPeters et al, 2016;Royer et al, 2016;Wyart and Cates, 2014].…”

Uncovering Instabilities in the Spatiotemporal Dynamics of a Shear-Thickening Cornstarch Suspension

“…While the shear-induced growth of particle clusters, referred to as "hydroclusters," has long been invoked to explain shear thickening, especially in Brownian suspensions of small colloidal particles [11,12], it was recently recognized that shear thickening involves solid friction activated through shear-induced compressive stresses, at least for non-Brownian particles [13][14][15][16][17].…”

‘Shear thickening’ in non-shear flows: the effect of microstructure

“…The most recent success in the area has been the reproduction of the phenomenon of discontinuous shear thickening, the abrupt increase in the steady shear viscosity of a suspension when the shear rate is increased beyond some critical rate. It is now widely accepted that a key ingredient of the phenomenon is 'stress-induced friction' (Mari et al 2014;Wyart & Cates 2014), and this has been confirmed by experiment (Lin et al 2015;Clavaud et al 2017).…”