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

Scarratt, Liam R. J., Zhu, Liwen, Neto, Chiara
Langmuir 2019 v.35 no.8 pp. 2976-2982
atomic force microscopy, coatings, drainage, droplets, hydrodynamics, lubricants, oils, silicon, silicone, sucrose, wafers
Lubricant-infused surfaces have attracted great attention recently and are described as slippery liquid-infused porous surfaces (SLIPS). Here, we measured the hydrodynamic drainage forces on SLIPS by colloid probe atomic force microscopy (AFM) and quantified the effective slip length over a nanothin silicone oil layer on hydrophobized [octadecyltrichlorosilane (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 was 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 nano- and macroscale results reflect the immobilized nature of a silicone oil layer of thickness around 2 nm within an underlying monolayer. These results have important implications in the design of drag-reducing coatings using lubricant infusion.