Abstract
Superomniphobic surfaces, which repel droplets of polar and apolar liquids, are used for reducing frictional drag, packaging electronics and foods, and separation processes, among other applications. These surfaces exploit perfluorocarbons that are expensive, vulnurable to physical damage, and have a long persistence in the environment. Thus, new approaches for achieving superomniphobicity from common materials are desirable. In this context, microtextures comprising “mushroom-shaped” doubly reentrant pillars (DRPs) have been shown to repel drops of polar and apolar liquids in air irrespective of the surface make-up. However, it was recently demonstrated that DRPs get instantaneously infiltrated by the same liquids on submersion because while they can robustly prevent liquid imbibition from the top, they are vulnerable to lateral imbibition. Here, we remedy this weakness through bio-inspiration derived from cuticles of Dicyrtomina ornata, soil-dwelling bugs, that contain cuboidal secondary granules with mushroom-shaped caps on each face. Towards a proof-of-concept demonstration, we created a perimeter of biomimicking pillars around arrays of DRPs using a two-photon polymerization technique; another variation of this design with a short wall passing below the side caps was investigated. The resulting gas-entrapping microtextured surfaces (GEMS) robustly entrap air on submersion in wetting liquids, while also exhibiting superomniphobicity in air. To our knowledge, this is the first-ever microtexture that confers upon intrinsically wetting materials the ability to simultaneously exhibit superomniphobicity in air and robust entrapment of air on submersion. These findings should advance the rational design of coating-free surfaces that exhibit ultra-repellence (or superomniphobicity) towards liquids.
Highlights
Liquid-repellent surfaces are utilized in a broad spectrum of applications, such as preventing[1] and harvesting fog[2], removing bubbles from aqueous feeds[3], fluid drag reduction and self-cleaning[4], preventing adhesion of barnacles onto ship hulls[5], and anti-corrosion coatings[6], among others[7]
The apparent advancing contact angles on gas-entrapping microtextured surfaces (GEMS) were θA> 150°; the liquid-solid work of adhesion was minimal as evidenced by the bouncing off of droplets dropped from a height of h ≈ 3 mm and contact angle hysteresis, www.nature.com/scientificreports
This is the first-ever demonstration of a microtexture derived from an intrinsically wetting material that exhibits superomniphobicity in terms of contact angles and robustly entraps air upon immersion
Summary
Liquid-repellent surfaces are utilized in a broad spectrum of applications, such as preventing[1] and harvesting fog[2], removing bubbles from aqueous feeds[3], fluid drag reduction and self-cleaning[4], preventing adhesion of barnacles onto ship hulls[5], and anti-corrosion coatings[6], among others[7]. Liu & Kim introduced a microtexture that exhibits superomniphobicity regardless of their surface chemistry[24] They microfabricated mushroom-shaped pillars[25,26], known as doubly reentrant pillars (DRPs), onto SiO2/Si wafers and measured advancing and receding contact angles of a variety of liquids with surface tensions as low as 10 mN/m and found them to be θA > 150° and as θA − θR ≤ 10°. We employ a two-photon polymerization technique to realize arrays of DRPs surrounded by a boundary of Dicyrtomina ornata-inspired pillars that have mushroom-shaped caps on top and laterally Variations of this design are presented towards a proof-of-concept demonstration of microtextured surfaces, derived from intrinsically wetting materials that can entrap air robustly on immersion and exhibit superomniphobicity against liquid droplets in air. We refer to these gas entrapping microtextured surfaces by the acronym GEMS
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