Slip and Flow in Soft Particle Pastes

Abstract

Concentrated dispersions of soft particles are shown to exhibit a generic slip behavior near smooth surfaces. Slip results from a balance between osmotic forces and noncontact elastohydrodynamic interaction between the squeezed particles and the wall. A model is presented that predicts the slip properties and provides insight into the behavior of the bulk paste.

Yielding and Flow in Adhesive and Nonadhesive Concentrated Emulsions

“…The flow of a non-adhesive, glassy emulsion was shown to remain homogeneous throughout the yielding transition, very much like the microgel pastes of Ref. [15] but contrary to numerical predictions [13,14]. This discrepancy could be ascribed to (i) the fact that emulsion droplets are deformable while model glasses are composed of hard spheres, (ii) the size of the experimental gap which contains about 3 10 3 droplets whereas simulations use only 100 particles at most in the velocity gradient direction, and (iii) the absence of lubricating layers and wall slip in numerical models, which may play a crucial role [15].…”

“…Indeed microgel pastes [15] and soft colloidal gels of star polymers [16] were shown to flow homogeneously in the vicinity of yielding (although intermittent jammed states were also reported in the latter case). This raises the question of the sensitivity of the flow behavior to the nature of the interactions between the sample constituents i.e.…”

“…[15] but contrary to numerical predictions [13,14]. This discrepancy could be ascribed to (i) the fact that emulsion droplets are deformable while model glasses are composed of hard spheres, (ii) the size of the experimental gap which contains about 3 10 3 droplets whereas simulations use only 100 particles at most in the velocity gradient direction, and (iii) the absence of lubricating layers and wall slip in numerical models, which may play a crucial role [15]. When droplets are made to interact strongly through short-range attraction, the resulting attractive glass displays solid-liquid coexistence, wall slip, and shear localization in a large range of stresses, which makes it hard to precisely define a yield stress.…”

A mesoscopic model for the rheology of soft amorphous solids, with application to microchannel flows

“…But these structural changes for the material at rest imply a decrease of the fluidity at the wall, as opposed to the enhancement that is experimentally observed by Goyon 39 and Géraud 46 at high enough stresses, i.e., where the largest deviations occur. Alternatively, the specific behaviour at the wall is often rationalised by the existence of a depleted 'lubrication layer' close to the wall, as is often found in sheared dispersions [60][61][62][63][64][65][66] . This phenomenon is more acute for deformable particles 62 undergoing high shear rates and/or high shear gradients; it generates an apparent wall slip.…”

“…39,[44][45][46] the size of surface asperities was a couple of microns at most, that is, significantly less than the typical "particle" size, which plausibly favours slip, as well as the high shear rates experienced at the microchannel walls. Nevertheless, recent theories of slip along smooth walls involved, in addition, parameters such as the deformability of the droplets, 63,64 and the particle-wall interactions 74 , not to mention the presumably significant impact of Brownian motion in cases where it is relevant 75,76 . As far as we know, the somewhat daunting challenge to extend these theories to the case of rough walls still awaits a successful accomplisher.…”