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Edited by William R. Schowalter, Princeton University, Princeton, NJ, and approved August 30, 2012 (received for review April 21, 2012)
Abstract
We report a simple correlation between microstructure and strain-dependent elasticity in colloidal gels by visualizing the evolution of cluster structure in high strain-rate flows. We control the initial gel microstructure by inducing different levels of isotropic depletion attraction between particles suspended in refractive index matched solvents. Contrary to previous ideas from mode coupling and micromechanical treatments, our studies show that bond breakage occurs mainly due to the erosion of rigid clusters that persist far beyond the yield strain. This rigidity contributes to gel elasticity even when the sample is fully fluidized; the origin of the elasticity is the slow Brownian relaxation of rigid, hydrodynamically interacting clusters. We find a power-law scaling of the elastic modulus with the stress-bearing volume fraction that is valid over a range of volume fractions and gelation conditions. These results provide a conceptual framework to quantitatively connect the flow-induced microstructure of soft materials to their nonlinear rheology.
Footnotes
- ↵1To whom correspondence should be addressed. E-mail: mjsolo{at}umich.edu.
Author contributions: L.C.H. and M.J.S. designed research; L.C.H., R.S.N., S.C.G., and M.J.S. performed research; L.C.H., R.S.N., S.C.G., and M.J.S. contributed new reagents/analytic tools; L.C.H., R.S.N., S.C.G., and M.J.S. analyzed data; and L.C.H., R.S.N., S.C.G., and M.J.S. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1206742109/-/DCSupplemental.
Isostaticity and elasticity of colloidal gels
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