Large Effective Slip on Lubricated Surfaces Measured with Colloidal Probe AFM

Abstract

In this work, we study the interfacial boundary conditions at the interface between two immiscible liquids under a laminar flow. We measure the hydrodynamic drainage forces acting on a colloid probe as it approaches a flat and smooth Teflon film coated with silicone oil films, submerged in a sucrose solution using atomic force microscopy. On Teflon substrates, silicone oil films of thickness several hundred nanometers could be stabilized, and we found the effective slip length over these to be of the order of several hundred nanometers which increases with increasing silicone oil film thickness, as expected. The fitted slip length values weakly increased with increasing shear rates. The high values of effective slip length indicate that lubricant-infused surfaces are likely to reduce drag on length scales that approach the macroscopic scales.

Nanobubbles explain the large slip observed on lubricant-infused surfaces

“…On LIS, higher flow rates increase the portions of exposed areas of the Teflon substrate to the water and, therefore, we expect that higher flow also increases nucleation site density. Our previous colloid probe AFM measurements 14,15 and our current microfluidic experiments on smooth infused surfaces did not show higher than expected slip length values. This corroborates the need for surface roughness for substantial air nucleation to occur in LIS.…”

“…(i) This effect is expected to be nanoscale, as suggested by molecular dynamics simulations [28][29][30] and experiments 14,15 , and not quantifiable with our experimental setup.…”

“…The larger the slip length b, the larger the reduction in frictional drag. Superhydrophobic 4,5 and lubricant-infused surfaces (LIS) [6][7][8] have been shown to reduce drag substantially [9][10][11][12][13][14][15] , which makes them attractive to reduce the energy required to drive flow. Drag reduction by these surfaces is explained with the reduced contact area between the solid and the fluid 9 , which results in an "apparent slip" of the flowing liquid of viscosity μ w over the air (in the case of superhydrophobic surfaces) or over a lubricant of lower viscosity μ o in LIS, compared to the case of a solid surface.…”

Intrinsic and apparent slip at gas-enriched liquid–liquid interfaces: a molecular dynamics study

“…Due to its incompressibility, this liquid layer does not suffer from the fragility of the superhydrophobic state, while maintaining many of its favourable properties (Mistura & Pierno 2017;Semprebon, McHale & Kusumaatmaja 2017). For instance, recent works have predicted (Asmolov, Nizkaya & Vinogradova 2018) or measured large apparent slip lengths at LIS (Solomon, Khalil & Varanasi 2014;Scarratt, Zhu & Neto 2020) and even potential for turbulent drag reduction (Fu et al 2017;Cartagena et al 2018). In particular, some of the recently reported values of the slip length at oil-infused surfaces are surprisingly large, up to 250 nm (Scarratt et al 2020), which urgently calls for a thorough investigation of its microscopic origin.…”

“…For instance, recent works have predicted (Asmolov, Nizkaya & Vinogradova 2018) or measured large apparent slip lengths at LIS (Solomon, Khalil & Varanasi 2014;Scarratt, Zhu & Neto 2020) and even potential for turbulent drag reduction (Fu et al 2017;Cartagena et al 2018). In particular, some of the recently reported values of the slip length at oil-infused surfaces are surprisingly large, up to 250 nm (Scarratt et al 2020), which urgently calls for a thorough investigation of its microscopic origin. Is it due to intrinsic slip at the liquid-liquid interface?…”