Jamming Distance Dictates Colloidal Shear Thickening

Abstract

We report the steady state viscosity and contact microstructure of dense suspensions containing hardparticle poly(methyl methacrylate) (PMMA) colloids with tunable surface morphologies. Structural analysis of confocal micrographs shows that the contact number deficit Δz scales as the jamming distance Δϕ, where the scaling relations contain a range of exponents that describe the compactability of frictional packings with jamming fractions ϕJ and jamming contact numbers zJ. Suspensions with rougher particles require fewer nearest neighbors than that of smoother particles to reach the jamming point. Agreement between model predictions from a mean-field theory and our rheological data shows that shear thickening is modeled by different types of frictional packings that form under applied shear stresses. The shear thickening strength, quantified by the slope of the viscosity-stress flow curves, scales with the jamming distance for a broad class of dense suspensions comprising PMMA smooth and rough colloids, silica smooth and rough colloids, and simulations with interparticle friction or surface asperities. Our results suggest that Δϕ/ϕJ = 0.1 and Δz/zJ = 0.5 is the point at which hydrodynamics, Brownian forces, and friction become equally important in colloidal shear thickening.

Ordered domains in sheared dense suspensions: the link to viscosity and the disruptive effect of friction

“…This behavior is in stark contrast with the thinning we observed without friction (see Fig. 2), and in agreement with the results of previous studies which indicate that friction is the key to shear thickening [1,4,[22][23][24][25][26].…”

“…l l l m 1 m 2 m 3 q lm1 (i)q lm2 (i)q lm3 (i) (4) where the coefficients are the Wigner 3-j coefficients and the sum is over values such that m 1 + m 2 + m 3 = 0. Specifically, the set of {q 4 , q 6 , ŵ4 , ŵ6 } are generally sufficient to characterize the order of colloidal systems.…”

“…Examples include concrete, pharmaceuticals, blood, and more. Dilute suspensions typically exhibit liquid-like behavior, but when the volume fraction of suspended particles is high, complex rheological properties arise [1][2][3][4]. Understanding and controlling this behavior is of academic interest and crucial for many industrial applications.…”

“…In addition, at high densities many suspensions exhibit shear thickening properties [1,4,[19][20][21]. This is generally associated with cluster formation and contact forces between particles.…”

“…This rise in viscosity is called continuous shear thickening (CST) or dis-continuous shear thickening (DST), depending on how rapidly the viscosity rises with shear rate. There is substantial evidence that frictional forces, due to particle roughness, play a key role in the shear thickening phenomenon, with DST being attributed to a sharp rise in the number of frictional contacts [1,2,4,[22][23][24].…”