Disentangling the roles of roughness, friction and adhesion in discontinuous shear thickening by means of thermo-responsive particles (2004.05970v1)

Abstract: Dense suspensions of colloidal or granular particles can display pronounced non-Newtonian behaviour, such as discontinuous shear thickening (DST) and shear jamming (SJ). The essential contribution of particle surface roughness and adhesive forces confirms that stress-activated contacts can play a key role in these phenomena. By employing a system of microparticles coated by responsive polymers that allow friction, adhesion, and surface roughness to be selectively and independently tuned as a function of temperature, we offer a way to disentangle these contributions. We find that DST occurs at lower shear rates when friction and adhesion between particles are enhanced at high temperatures. Additionally, the temperature-responsive polymers provide lubricity at low temperatures that can mask surface roughness. The link between single-particle properties and macroscopic rheology is elucidated via lateral force microscopy, which reveals the nature of rheologically relevant contact conditions. In situ temperature tuning during shear allows contact conditions to be modified, and DST to be switched on and off on demand. These findings strengthen our understanding of the microscopic parameters affecting DST and identify new routes for the design of smart, non-Newtonian fluids.