(242f) Shear-Driven Ordering and Disordering of 2D Frictional Sphere Suspensions

Dense suspensions are ubiquitous in natural, biological, and industrial systems. Most studies of dense suspensions of frictional spheres are restricted to bidisperse/polydisperse systems in order to avoid ordering.^1,2 However, in certain contexts ordering could be desirable, for example to obtain useful optical, photonic or plasmonic properties.^3,4 Thus, it is important to study what microscopic constraints can affect the ordering of particles. In this study we analyze the ordering process for the two-dimensional case, and how it is disrupted with local activation of friction. The lubricated-flow discrete element method (lf-DEM) simulation¹ comprise of inertia-less spheres with short-range repulsion, short-range lubrication and stress-activated friction. We implement frictional constraints in two different ways: sliding and rolling.⁵ Initially, we focus on the effect of sliding friction alone. For a range of high packing fractions, observe that there exist two qualitatively different regimes.

At low shear stresses, when hydrodynamics is dominant, the particles form layered assemblies that exhibit ordered waves transmitting along the flow direction. The particles oscillate between hexagonal and square order in order to flow in a worm-like cooperation. This results in a moderate degree of long-range order in the flowing state. In contrast, at higher shear stress, as friction gets activated, the system transitions to a less ordered state with transient hexagonally packed microdomains. The worm-like cooperative motion is largely absent, along with a general absence of long-range order.
The transition between these two states is then explored for rate-controlled and stress-controlled simulations, revealing an abrupt and continuous change in global hexatic order parameter, respectively. The intermediate states between the two regimes are also characterized to ascertain the degree of heterogeneity in ordering. The distinction between the two states gradually disappears at lower packing fractions as the low-shear regime becomes more and more disordered.

Introducing rolling friction further constrains the motion of these particles and disrupts order in a qualitatively distinct manner compared to sliding friction alone. Rolling friction can lead to drastic rupture of closed packed domains. This model sets up the groundwork for more realistic studies in shear-induced ordering in rough particulate materials and colloids that may involve various frictional constraints.

(1) Mari, R.; Seto, R.; Morris, J. F.; Denn, M. M. Shear Thickening, Frictionless and Frictional Rheologies in Non-Brownian Suspensions. Journal of Rheology 2014, 58, 1693–1724.

(2) Singh, A.; Mari, R.; Denn, M. M.; Morris, J. F. A Constitutive Model for Simple Shear of Dense Frictional Suspensions. Journal of Rheology 2018, 62, 457–468.

(3) Cersonsky, R. K.; Dshemuchadse, J.; Antonaglia, J.; van Anders, G.; Glotzer, S. C. Pressure-Tunable Photonic Band Gaps in an Entropic Colloidal Crystal. Physical Review Materials 2018, 2, 125201.

(4) Kempa, T. J.; Kim, S. K.; Day, R. W.; Park, H. G.; Nocera, D. G.; Lieber, C. M. Facet-Selective Growth on Nanowires Yields Multi-Component Nanostructures and Photonic Devices. J Am Chem Soc 2013, 135, 18354–18357.

(5) Singh, A.; Ness, C.; Seto, R.; de Pablo, J. J.; Jaeger, H. M. Shear Thickening and Jamming of Dense Suspensions: The “Roll” of Friction. Physical Review Letters 2020, 124.