The effect of sphere roughness on the rheology of concentrated suspensions

•Newtonian and Boger fluid matrices were used in suspensions of rough spheres.•The effect of roughness on shear rheology was investigated.•Increasing roughness increased both viscosity and normal stresses. We present the results of measuring the viscometric flow of concentrated rigid-sphere suspensions with constant-viscosity matrices, both Newtonian (silicone oil) and non-Newtonian (Boger fluid: corn syrup (79.4%)–glycerin (19.8%)–4%PAA water (0.78%)). Various problems with the measurements are discussed, including settling due to density differences. The effect of sphere roughness on shear rheology is a main concern of the work. The viscosities of silicone oil and Boger fluid suspensions were increased by increasing sphere roughness, and the normal stress difference N1−N2 in the Boger fluid suspension also increased with roughness.