Surface Roughness and Hydrodynamic Boundary Slip of a Newtonian Fluid in a Completely Wetting System

Abstract

The influence of surface roughness on the boundary condition for the flow of a Newtonian fluid near a hard wall has been investigated by measurement of the hydrodynamic drainage force. The degree of slip is found to increase with surface roughness. This leads to the conclusion that in most practical situations boundary slip takes place, leading to a reduction of the drainage force.

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.…”

“…The surface is said to be hydrophobic if θ c > 90 • , and in that case the nucleation of small bubbles in the liquid should occur preferentially on the surface. Slip has been measured for systems in complete wetting [17,18,67,68,125,126] and partial wetting [9,16,29,31,32,33,34,38,39,40,67,87,88,68,108,116,150,162,163,178,192,194,195]. The amount of slip has usually been found to increase with contact angle, either systematically (e.g., [192]) or only for non-polar liquids [31].…”

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

“…(In fact it was shown later that roughness has a much more drastic effect [1032].) To exclude this Bonaccurso et al [190] measured hydrodynamic effects between borosilicate glass particles and mica or silicon oxide in aqueous medium.…”

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].…”