Exploring the roles of roughness, friction and adhesion in discontinuous shear thickening by means of thermo-responsive particles

Abstract

Dense suspensions of colloidal or granular particles can display pronounced non-Newtonian behaviour, such as discontinuous shear thickening and shear jamming. The essential contribution of particle surface roughness and adhesive forces confirms that stress-activated frictional contacts can play a key role in these phenomena. Here, by employing a system of microparticles coated by responsive polymers, we report experimental evidence that the relative contributions of friction, adhesion, and surface roughness can be tuned in situ as a function of temperature. Modifying temperature during shear therefore allows contact conditions to be regulated, and discontinuous shear thickening to be switched on and off on demand. The macroscopic rheological response follows the dictates of independent single-particle characterization of adhesive and tribological properties, obtained by colloidal-probe atomic force microscopy. Our findings identify additional routes for the design of smart non-Newtonian fluids and open a way to more directly connect experiments to computational models of sheared suspensions.

Leveraging the polymer glass transition to access thermally-switchable shear jamming suspensions

“…Around 𝑇𝑇 g , adhesive interactions increase on account of an increase in true contact area, which may lead to stronger cohesive 'sticky' forces and enhanced rolling friction 21,31,32 . On account of the viscoelastic nature of the interface between two particles sheared into contact, the friction coefficient (𝜇𝜇) can either increase monotonically with 𝑇𝑇 at moderate to high surface deformation rates, or show a peak if the deformation rate is slow enough to cross over into the time scale of surface relaxation [32][33][34][35] .…”

“…Typical materials for the particles include silica 11,14 , glassy polymers like poly(methyl methacrylate) (PMMA) 6,15 or polystyrene (PS) 16,17 , or rigid non-spherical granular materials like cornstarch 9 . In such systems, key factors that determine DST and SJ include applied stress (𝜏𝜏), volume fraction (𝜙𝜙), and interparticle friction 3,14,15,[17][18][19][20][21][22][23] .…”

“…For strong shear thickening and shear jamming, where 𝜙𝜙 is high and frictional contact forces are crucial, recent studies have shown that the chemical composition and structure of the particle surfaces can affect contact interactions and drastically influence the rheological behavior 14,15,19,21 . While these works and related studies 12,24,25 have contributed towards a better understanding of the structure-property relationship during DST and SJ, little is known about the roles of particle and interfacial compliance.…”

Stimuli-responsive surfaces for switchable wettability and adhesion

“…However, the non-Newtonian fluids (e.g. biofluid, some saline solutions, some polymeric solutions) show different behavioural trends in response to external forces, especially on hydrophilic surfaces [155]. Only when the behaviour of non-Newtonian fluids are widely investigated can more potential applications of smart surfaces be realized.…”

Engineering hybrid microgels as particulate emulsifiers for reversible Pickering emulsions

“…Microgels are soft and deformable colloid particles that can swell or shrink in a solvent with external stimulus. [1][2][3][4] Touted as intelligent materials, microgels have received great attention 5,6 and have been employed as rheology modifiers, 7,8 delivery vehicles, 9 emulsion stabilizers, 10,11 micropattern templates, 12 microreactors, 13 and actuators. 14 Particularly, microgels are capable of spontaneously self-assembling onto the oil/water interface and rapidly lowering the interfacial energy, [15][16][17] and Ngai et al pioneered the use of poly(N-isopropylacrylamide-comethacrylic acid) (PNIPAM-co-MAA) microgels for stabilization of pH and temperature responsive oil-in-water (o/w) Pickering emulsion in 2004.…”