Jamming distance, contact networks, and shear thickening of frictional colloids

We report a series of experimental studies on the rheology and contact network of dense suspensions containing model colloids with tunable surface roughness. Our results suggest that the jamming distance is a universal parameter that normalizes the shear thickening and linear viscoelasticity of frictional and frictionless colloids. To obtain these results, sterically stabilized poly(methyl methacrylate) (PMMA) colloids are suspended in the solvent squalene to provide hard sphere interactions and refractive index matching. A customized confocal rheometer setup is used to generate 3D images of contact networks in shear thickening dense suspensions. Computational results from dissipative dynamics simulations, where rough colloids are modeled as small asperities integrated with a core particle, are in excellent agreement with experimental data. Structural analysis performed on quiescent and sheared suspensions show that for all surface roughness parameters, the shear thickening strength quantified by the slope of the viscosity-stress flow curves shows a universal scaling with jamming distance and the dynamic contact number for a broad class of dense colloidal suspensions. This statement is supported not only by PMMA colloids with hard and charged interactions, but also by other types of colloidal suspensions from the literature, as well as multiple computer simulations on shear thickening.