Shear-Dependent Boundary Slip in an Aqueous Newtonian Liquid

Abstract

We report direct measurements of hydrodynamic drainage forces, which show clear evidence of boundary slip in a Newtonian liquid. The degree of boundary slip is found to be a function of the liquid viscosity and the shear rate, as characterized by the slip length, and is up to approximately 20 nm. This has implications for confined biological systems, the permeability of microporous media, and for the lubrication of nanomachines, and will be important in the microcontrol of liquid flow. We also show that current theories of slip do not adequately describe the experimental data.

Microfluidics: The No-Slip Boundary Condition

“…The conclusions have been confirmed by Molecular Dynamics simulations [135] and are consistent with studies of flow in capillaries with diameters of tens of nanometers [3,91]. In this context, the large number of recent published experiments reporting some form of (apparent) slip with λ ∼ 1 nm−1 µm in the flow of Newtonian liquids is surprising [9,16,17,18,29,30,32,33,38,39,40,67,87,88,68,108,116,125,126,150,162,163,178,192,193,194,195], and has allowed to re-discover a few early [29] Poly(carbonate)+PVP SDS solutions studies reporting some degree of slip [21,34,46,141,160]. In part, this chapter is an attempt to describe and interpret these more recent experimental results.…”

“…Other more complex behaviors remain to be understood, including dependence of the results on the molecular shape and size [30,55,68,195], probe size [108], or viscosity [40,116]. The development of alternative direct experimental methods would allow for a more precise quantification of slip phenomena.…”

Force measurements with the atomic force microscope: Technique, interpretation and applications

“…For strong liquid-wall interactions AFM results indicate that also slip occurs. Significant slip lengths of up to 20 nm were found by Craig et al in aqueous sucrose solutions (viscosities of 0.01-0.08 Pa s) [1031]. They measured hydrodynamic forces between gold coated silica spheres and gold coated mica.…”

Apparent Slip Due to the Motion of Suspended Particles in Flows of Electrolyte Solutions

“…Over the last few years, a number of pressure-driven flow [7,8,9,10], shear-flow [11], and squeeze-flow experiments [12,13,14,15,16,17,18] showing a response interpretable as some degree of slip for partially wetting liquids have been reported. Molecular dynamics simulations of Lennard-Jones liquids have also shown that slip can occur, but only at unrealistically high shear rates [19,20].…”

“…The first consists in performing indirect measurements, such as pressure-drop versus flow rate or squeezing rate versus resistance, and then use such measurements to infer a slip length. This procedure is indirect in the sense that it assumes that the flow resembles (2) and then equation (3), or an equivalent, is used to determine λ [7,8,10,12,13,14,15,16,17,18].…”