(6az) Engineering the Flow Behavior of Colloidal Materials through Surface Modification and Shape Anisotropy

The idea that colloidal materials can be designed with enhanced rheological properties by incorporating shape and surface anisotropy is motivated by our finding that structural rigidity can be used to predict the nonlinear elasticity in gels that have undergone yielding. We demonstrate that the predictive power of microscopic theories can be improved when both the microstructural rigidity and the dynamical heterogeneity induced by yielding are taken into account. Because thermal rupture forces play a critical role in yielding, we develop a model gel system in which rheological measurements can be carried out in conjunction with microscopy experiments and direct force measurements using optical tweezers. The validity of structural rigidity is also tested by synthesizing colloidal spheroids and roughened particles. We find that colloidal oblate spheroids self-assemble into tilted structures in a specific range of volume fractions and attraction strengths. These structures could pave the way for maintaining the elasticity of colloidal gels even at exceedingly low particle loading. Finally, we observe a significant increase in the shear thickening behavior of rough colloids in concentrated suspensions. These results collectively provide experimental support for the applicability of structural rigidity as a guiding principle in engineering the flow properties of a broad range of soft matter.