dataPlusPythonNotebook.zip

We present a simple route to obtain large quantities of suspensions of non-Brownian particles with stim-uli-responsive surface properties to study the relation between their flow and interparticle interactions. Weperform an alkaline hydrolysis reaction on poly(methyl methacrylate) (PMMA) particles to obtain poly(sodiummethacrylate) (PMAA-Na) particles. We characterize the quasi-static macroscopic frictional response of theiraqueous suspensions using a rotating drum. The suspensions are frictionless when the particles are dispersedin pure water. We relate this state to the presence of electrosteric repulsion between the charged surfaces ofthe ionized PMAA-Na particles in water. Then we add monovalent and multivalent ions (Na+, Ca2+, La3+)and we observe that the suspensions become frictional whatever the valency. For divalent and trivalent ions,the quasi-static avalanche angle θc at large ionic strength is greater than that of frictional PMMA particles inwater, suggesting the presence of adhesion. Finally, a decrease in the pH of the suspending solution leads toa transition between a frictionless plateau and a frictional one. We perform Atomic Force Microscopy (AFM)to relate our macroscopic observations to the surface features of the particles. In particular, we show that theincrease in friction in the presence of multivalent ions or under acidic conditions is driven by a nanoscopicphase separation and the bundling of polyelectrolyte chains at the surface of the particle. Our results highlightthe importance of surface interactions in the rheology of granular suspensions. Our particles provide a simple,yet flexible platform to study frictional suspension flows.