Slippery surfaces: A decade of progress

Abstract

Slippery surfaces have received great attention for more than a quarter-century. In particular, during the last decade, interest has increased exponentially, resulting in thousands of articles concerning three types of slippery surfaces: superhydrophobic, superoleophobic, and omniphobic. This review focuses on recent developments and significant findings in naturally inspired slippery surfaces. Superhydrophobicity can be characterized by water droplets beading on a surface at significantly high static contact angles and low contact-angle hystereses. Microscopically rough hydrophobic surfaces could entrap air in their pores, resulting in a portion of a submerged surface with an air–water interface, which is responsible for the slip effect and drag reduction. Suberhydrophobicity enhances the mobility of droplets on lotus leaves for self-cleaning purposes, the so-called lotus effect. Surface hydrophobicity can be advanced to repel low-surface-tension liquids, i.e., become superoleophobic. Another kind of slippery coating is the slippery liquid-infused porous surfaces (SLIPS), which are omniphobic coatings. Certain plants such as the carnivorous Nepenthes pitcher inspired SLIPS. Their interior surfaces have microstructural roughness, which can lock in place an infused lubricating liquid. The lubricant is then utilized as a repellent surface for other liquids or substances such as water, blood, crude oil, ice, insects, and bio-fouling. In this review, we discuss different slippery mechanisms in nature. We also cover recent advances in manufacturing, texturing, and controlling slippery surface at the micro- and nanoscales. We further discuss the performance, sustainability, and longevity of such surfaces under different environmental conditions. Very-recent techniques used to characterize the surfaces are also detailed.

A dual‐action nitric oxide‐releasing slippery surface for extracorporeal organ support: Dynamic in vitro hemocompatibility evaluation

“…It has been shown that exposure to blood does not affect the NO release of NO-releasing polymers. 9,29 Considering the post-exposure NO fluxes follow previous LINO NO-release kinetics (without the presence of blood), 22 we can attribute the drop in post-exposure NO flux to normal NO-kinetics. Importantly, sub-endothelial NO fluxes have been shown to have a significant bioactive effect, 30 thus while the NO flux decreased this does not imply that the tubing was not bioactive.…”

“…14 It is also possible that the lower RPMs can be attributed to improved flow dynamics on slippery surfaces. 22 The effect of LINO on platelets was of particular interest in this study due to the known function of NO to maintain platelet quiescence in the endothelium. We found that at 6 h the concentration of activated P-selectin expressing platelets was significantly lower in both NO-releasing groups (NO, LINO) compared to CTRL, and reduction in platelet count was delayed in the NO-releasing groups versus CTRL and LI.…”

“…Silicone oil swells the silicone polymer and increases its mass by ~1.5–1.7×, which is increased further in SNAP‐impregnated polymers 14 . It is also possible that the lower RPMs can be attributed to improved flow dynamics on slippery surfaces 22 …”

Numerical and experimental investigation of static wetting morphologies of aqueous drops on lubricated slippery surfaces using a quasi-static approach

“…For more than a decade, lubricant-infused slippery surfaces inspired by Nepenthes' pitcher plants have gained a lot of attention. [1][2][3] The surfaces comprise a solid substrate with micro/nano textures infused with a highly spreading lubricating fluid (oil) that is immiscible with other test liquids (aqueous). When drops of a test liquid come into contact with such surfaces, different configurations of the lubricating oil film and, subsequently, the drops have been theoretically predicted and experimentally verified.…”

Two local slip modes at the liquid–liquid interface over liquid-infused surfaces

“…32 They also reported a drag reduction rate that was exceeded 35% for LISs and demonstrated that drag reduction increased with increasing viscosity ratio, groove width, fluid area, and Reynolds number. 33 There are three criteria to design slippery LISs: 34,35 (1) the lubricant liquid should wick into, wet, and stably adhere within the substrate, (2) the solid must be preferentially wetted by the lubricant liquid rather than by the working liquid that needs to be repelled, and (3) the lubricant fluid and working fluid must be immiscible. Since the lubricant is always insoluble in water when the LISs are submerged under water, the LLI is more stable than the GLI and, thus, becomes more advantageous for drag reduction.…”