Shear thickening in colloidal dispersions

Abstract

The popular interest in cornstarch and water mixtures known as "oobleck" after the complex fluid in one of Dr. Seuss's classic children's books arises from their transition from fluid-like to solid-like behavior when stressed. The viscous liquid that emerges from a roughly 2-to-1 (by volume) combination of starch to water can be poured into one's hand. When squeezed, the liquid morphs into a doughy paste that can be formed into shapes, only to "melt" into a puddle when the applied stress is relieved. Internet videos show people running across a large pool of the stuff, only to sink once they stop in place, and "monsters" that grow out of the mixture when it's acoustically vibrated (for an example, see the online version of this article). Shear-thickening fluids certainly entertain and spark our curiosity, but their effect can also vex industrial processes by fouling pipes and spraying equipment, for instance. And yet, when engineered into composite materials, STFs can be controlled and harnessed for such exotic applications as shockabsorptive skis and the soft body armor discussed in box 1. Engineers and colloid scientists have wrestled with the scientific and practical problems of shear-thickening colloidal dispersions-typically composed of condensed polymers , metals, or oxides suspended in a liquid-for more than a century. More recently, the physics community has explored the highly nonlinear materials in the context of jamming 1 (see the article by Anita Mehta, Gary Barker, and Jean-Marc Luck in PHYSICS TODAY, May 2009, page 40) and the more general study of colloids as model systems for understanding soft condensed matter. Hard-sphere colloids are the "hydrogen atom" of colloidal dispersions. Because of their greater size and interaction times compared with atomic and molecular systems, colloidal dispersions are often well suited for optical microscopy and scattering experiments using light, x rays, and neutrons. That makes the dispersions, beyond their own intrinsic technological importance, ideal models for exploring equilibrium and near-equilibrium phenomena of interest in atomic and molecular physics-for example, phase behavior and "dynamical arrest," in which particles stop moving collectively at the glass transition. The relevance of colloids to atomic and molecular systems breaks down, though, for highly nonequilibrium phenomena. Indeed, shear thickening in strongly flowing colloidal dispersions may be among the most spectacular, and elucidating, examples of the differences between the systems.

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

“…Increasing the particles' concentration beyond dilute limit leads to the activation of particle-particle interactions and the creation of long range order, resulting in nonNewtonian effects such as shear thinning or shear thickening. These effects can be explained with transitions from an ordered to a disordered state that occur when high stresses are applied [10]. Indeed, when this fluid is subjected to a relatively low shear rate, the repulsive interactions between particles are able to create an ordered and layered structure that consents a more effective particles flow through the liquid phase, reducing the viscosity of the solution.…”

“…As a consequence, if we consider a single particle of the dispersed phase, it is possible to correlate its diffusion through the continuous phase with the thermal energy and its mobility μ (the ratio of the particle's terminal drift velocity to an applied force) by following the Stokes-Einstein-Sutherland fluctuation-dissipation relationship, as discussed by Wagner et al [10]:…”

Discontinuous Shear Thickening in Cornstarch Suspensions

“…Recent works thus suggest that it is a dynamic or shear jamming transition, which motivates a considerable attention both from experiments [2], numerical simulation [3][4][5] and theory [6]. Shear thickening is also observed in dense colloidal suspension, where it has been related to the formation of dense clusters of particles [7][8][9]. In these systems, the competition between shear induced cluster formation and Brownian motion that homogenizes the suspension naturally determine a critical shear rate for the onset of shear thickening.…”

The rheology of shear thickening fluids with various ceramic particle additives

“…These suspensions only displayed shear thinning behavior for each temperature level. According to early studies [2], [18], [42], thickening gradually vanishes as the silica loading in the suspension decreases, in fact, the inclusion of additives deducts the volume fraction of the silica from the suspension, thereby adversely affecting the thickening mechanism. It is therefore possible that the volume fraction of silica falls below the effective concentration, thus triggering thickening for the suspension with 25wt% (14.24vol%) loading of B4C particles.…”