Material constraints dictate flow mechanics in dense suspension rheology*

Why are we able to walk on top of "Oobleck fluids" without sinking? What properties of a hillslope dictate its failure? Answer to these questions lie in the ability to link the macroscopic forcing to corresponding microstructural changes in a given soft material. The rearrangement dynamics of the constituent building blocks for a given complex fluid is controlled by the constraints between them. Using model hard-sphere suspensions and heterogenous real-life slurries, we study the effects of the particle surface roughness and the chemical composition in the dense suspension flow behavior. We find that a physics-informed universal parameter, jamming distance, can unify flow behaviors, both in linear and non-linear rheological regimes. Connecting structure-property relationships, leveraging steady-shear rheometry and confocal microscopy, we find that parameters that restrict the constraints in particle motion, such as frictional and cohesive interactions, modifies the jamming distance for a given suspension mixture and dictate the overall flow characteristics, for e.g., yielding or shear thickening. Our work provides a powerful framework to encode flow properties in dense suspensions comprising of colloidal and granular materials and has applications ranging from designing flow behavior in household products to better predicting geophysical flows.