(299a) Toward Tailored Elasticity of Particulate Soft Matter by Control of Structural Rigidity

The mechanism of yielding in colloidal gels, particularly for high strain-rate deformations that are typical of practical applications, is not fully understood.  Recently, we have explored the concepts of isostaticity and structural rigidity as a guiding principle that can be used to understand and design the nonlinear elasticity in colloidal gels undergoing deformation.  In our studies, we impose simple shear flows of variable strain on colloidal particulate gels formed through depletion interactions.  We used in situ confocal laser scanning microscopy to characterize the resulting 3D microstructural changes. Contrary to methods based on ensemble-averaged parameters, we found that bond breakage in gels occurs mainly due to the erosion of rigid clusters that persist long after the gel has yielded.  We develop a simple correlation between the elastic modulus and the stress-bearing volume fraction that is valid over a range of volume fractions and gelation conditions.  We discuss implications of this successful correlation based on structural rigidity, including the effect of particle shape and roughness, as well as the indirect role of pair interactions on the non-linear elasticity of gelled particulate systems.