A review on wall slip in high solid dispersions

Abstract

High solid dispersions are soft materials made of colloidal or non colloidal particles dispersed at high volume fractions in a liquid matrix. They include hard sphere glasses, colloidal pastes, concentrated emulsions, foams, and vesicles. These materials are prone to exhibit different kinds of flow heterogeneities: shear-banding, wall slip, and fracture. While wall slip is often considered as a nuisance by experimentalists, it appears to be a fundamental component to the way that high solid dispersions respond to mechanical deformation. Moreover the ability of soft materials to slip onto surfaces allows them to move readily and efficiently in many natural phenomena and industrial processes. This review surveys recent developments and current research in the field. Topics like wall slip detection and control, microscopic modeling for rigid and soft particles materials, and the relation between wall slip and other flow heterogeneities are discussed. We also identify important open issues for future research.

Slow flows of yield stress fluids: yielding liquids or flowing solids?

“…A trend which can play an important role in YSF flows is wall slip, a situation in which the bulk moves as a rigid block along a smooth solid surface, the flow being concentrated in an extremely thin layer of material with a structure, and thus a behavior, differing from that of the bulk (Cloitre and Bonnecaze 2017). The structure of YSF, generally made of elements suspended in a liquid phase, is particularly well fitted to the development of this effect.…”

On the Enhancement of Heat Transfer and Reduction of Entropy Generation by Asymmetric Slip in Pressure-Driven Non-Newtonian Microflows

“…The slip velocity at wall "1" and wall "2" are then denoted by u w1 and u w2 , respectively. Thus, the velocity-stress relation at the channel walls takes the form (see also [10,Eq. (5)] and the discussion thereof):…”

“…On the basis of molecular dynamics simulations, Thompson and Troian [8] substantiated a generalized nonlinear slip boundary condition in which the slip length is a function of the shear rate, thereby generalizing the original slip law of Navier [9]. More recently, Cloitre and Bonnecaze [10] summarized the experimental approaches and evidence for nonlinear slip in flows of soft materials. Mathews and Hill [11] initiated the theoretical work on Newtonian fluids subject to a nonlinear slip boundary condition by finding, analytically, the velocity profile for three canonical pressure-driven flows: in a pipe, in an annulus and in a channel.…”

Roughness-Induced Friction on Liquid Foams

“…In rheology, the wall slippage of the probed material must be avoided to ensure that the dissipation is localized in the bulk of the sample. In the case of foams, a commonly adopted rule-of-thumb to prevent slippage consists in adding asperities larger than the bubble size on the walls [17], and to assert either visually [18] or by showing that the rheological measurements do not depend on the confinement [15,10], that there is no remaining slippage. This trial and error process is not always possible and the characterization of the effect of different roughness sizes has been studied for single wet bubbles on walls [6], but not for dry liquid foams.…”