Using high-speed confocal microscopy, we measure the particle positions in a colloidal suspension under large-amplitude oscillatory shear. Using the particle positions, we quantify the in situ anisotropy of the pair-correlation function, a measure of the Brownian stress. From these data we find two distinct types of responses as the system crosses over from equilibrium to far-from-equilibrium states. The first is a nonlinear amplitude saturation that arises from shear-induced advection, while the second is a linear frequency saturation due to competition between suspension relaxation and shear rate. In spite of their different underlying mechanisms, we show that all the data can be scaled onto a master curve that spans the equilibrium and far-from-equilibrium regimes, linking small-amplitude oscillatory to continuous shear. This observation illustrates a colloidal analog of the Cox-Merz rule and its microscopic underpinning. Brownian dynamics simulations show that interparticle interactions are sufficient for generating both experimentally observed saturations. © 2013 American Physical Society.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): KUS-C1-018-02
Acknowledgements: We thank D. Koch, L. Archer, I. Procaccia, G. Henchel, E. Bochbinder, B. Leahy, and J. L. Silverberg for helpful conversations. This work was supported in part by Award No. KUS-C1-018-02 from King Abdullah University of Science and Technology; the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award No. ER46517 (X.C.); and the National Science Foundation CBET-PMP Award No. 1232666. F.A.E. is grateful for computer cycles supplied by the Extreme Science and Engineering Discovery Environment, which is supported by National Science Foundation Grant No. OCI-1053575.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.