How Slippery are SLIPS? Measuring Effective Slip on Lubricated Surfaces with Colloidal Probe Atmoc Force Microscopy

Lubricant-infused surfaces have attracted great attention recently and are described as slippery (SLIPS). Here we measured hydrodynamic drainage forces on SLIPS by colloid probe atomic force microscopy (AFM) and quantified the effective slip length over a nano-thin silicone oil layer on hydrophobized (OTS-coated) silicon wafers. The thickness of a stable silicone oil film on OTS-Si under sucrose solution was determined to be 1.8 ± 1.3 nm, and found to induce an average effective slip length of 29 ± 3 nm, very close to that of an uninfused OTS substrate. These relatively low values of effective slip are confirmed by the relatively large macroscopic roll-off angle values of water droplets on the same substrates. Both the nano- and macro-scale results reflect the immobilized nature of a silicone oil layer of thickness around 2 nm within an underlying monolayer. These results have important implications for the design of drag-reducing coatings using lubricant infusion

A review on the mechanical and thermodynamic robustness of superhydrophobic surfaces

Advancements in the fabrication and study of superhydrophobic surfaces have been significant over the past 10 years, and some 20 years after the discovery of the lotus effect, the study of special wettability surfaces can be considered mainstream. While the fabrication of superhydrophobic surfaces is well advanced and the physical properties of superhydrophobic surfaces well-understood, the robustness of these surfaces, both in terms of mechanical and thermodynamic properties, are only recently getting attention in the literature. In this review we cover publications that appeared over the past ten years on the thermodynamic and mechanical robustness of superhydrophobic surfaces, by which we mean the long term stability under conditions of wear, shear and pressure. The review is divided into two parts, the first dedicated to thermodynamic robustness and the second dedicated to mechanical robustness of these complex surfaces. Our work is intended as an introductory review for researchers interested in addressing longevity and stability of superhydrophobic surfaces, and provides an outlook on outstanding aspects of investigation

Large Effective Slip on Lubricated Surfaces Measured with Colloidal Probe AFM

In this work, we study the interfacial boundary conditions at the interface between two immiscible liquids under 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 (AFM). On Teflon substrates, silicone oil films of thickness several hundred nm could be stabilized, and we found the effective slip length over these to be of the order of several hundred nanometers and increasing 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