  We present a simple route to obtain large quantities of suspensions of
non-Brownian particles with stimuli-responsive surface properties to study the
relation between their flow and interparticle interactions. We perform an
alkaline hydrolysis reaction on poly(methyl methacrylate) (PMMA) particles to
obtain poly(sodium methacrylate) (PMAA-Na) particles. We characterize the
quasi-static macroscopic frictional response of their aqueous suspensions using
a rotating drum. The suspensions are frictionless when the particles are
dispersed in pure water. We relate this state to the presence of electrosteric
repulsion between the charged surfaces of the 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 {\theta}c at
large ionic strength is greater than that of frictional PMMA particles in
water, suggesting the presence of adhesion. Finally, a decrease in the pH of
the suspending solution leads to a 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 the increase in friction in the presence of
multivalent ions or under acidic conditions is driven by a nanoscopic phase
separation and the bundling of polyelectrolyte chains at the surface of the
particle. Our results highlight the importance of surface interactions in the
rheology of granular suspensions. Our particles provide a simple, yet flexible
platform to study frictional suspension flows.
