Issue 12, 2014

Biaxial shear of confined colloidal hard spheres: the structure and rheology of the vorticity-aligned string phase

Abstract

Using a novel biaxial confocal rheoscope, we investigate the flow of the shear induced vorticity aligned string phase [X. Cheng et al., Proc. Natl. Acad. Sci. U. S. A., 2011, 109, 63], which has a highly anisotropic microstructure. Using biaxial shear protocols we show that we have excellent control of the string phase anisotropic morphology. We choose a shear protocol that drives the system into the string phase. Subsequently, a biaxial force measurement device is used to determine the suspension rheology along both the flow and vorticity directions. We find no measurable dependence of the suspension stress response along the shear and vorticity directions due to the hydrodynamically induced string morphology. In particular, we find that the suspension's high frequency stress response is nearly identical along the two orthogonal directions. While we do observe an anisotropic stress response at lower shear frequencies associated with shear thinning, we show that this anisotropy is independent of the shear induced string structure. These results suggest that for the range of flows explored, Brownian and hydrodynamic contributions to the stress arising from the anisotropic suspension microstructure are sufficiently weak that they do not significantly contribute to the rheology. Collectively, this study presents a general and powerful approach for using biaxial confocal rheometry to elucidate the relationship between microstructure and rheology in complex fluids driven far-from-equilibrium.

Graphical abstract: Biaxial shear of confined colloidal hard spheres: the structure and rheology of the vorticity-aligned string phase

Supplementary files

Article information

Article type
Paper
Submitted
14 Nov 2013
Accepted
13 Jan 2014
First published
14 Jan 2014

Soft Matter, 2014,10, 1969-1976

Biaxial shear of confined colloidal hard spheres: the structure and rheology of the vorticity-aligned string phase

N. Y. C. Lin, X. Cheng and I. Cohen, Soft Matter, 2014, 10, 1969 DOI: 10.1039/C3SM52880D

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