Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 109, Issue 40, Pages 16029-16034Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1206742109
Keywords
colloids; confocal microscopy; suspensions; shear flow
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Funding
- National Science Foundation, Division of Chemical, Bioengineering, Environmental, and Transport Systems Award [CBET 0853648]
- International Fine Particles Research Consortium
- Department of Defense/Assistant Secretary of Defense (Research and Engineering) [N00244-09-1-0062]
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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.
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