Designing bioinspired superoleophobic surfaces

Abstract

Nature provides a range of functional surfaces, for example, water-repellent or superhydrophobic surfaces, most common among them the lotus leaf. While water-repellency is widespread in nature, oil-repellency is typically limited to surfaces submerged in water, such as fish scales. To achieve oleophobicity in air, inspiration must be taken from natural structures and chemistries that are not readily available in nature need to be introduced. Researchers usually turn to fluorinated materials to provide the low surface energy that, when combined with bioinspired surface topography, is the key to unlocking oil-repellency. This review presents the state-of-the-art in the fabrication of superoleophobic surfaces.

Why re-entrant surface topography is needed for robust oleophobicity

“…The surface with this structure showed CAs above 150 • even for liquids with extremely low surface tension such as perfluorohexane (C 6 F 14 ) which has the lowest known liquid-air surface tension of γ LA = 10 mN m −1 [38,39].…”

“…The only known exceptions are certain species of leafhopper (they have high CA with diiodomethane and ethylene glycol, [42]) and springtails having a plastron layer formed around their body when they are immersed in olive oil [43]. Therefore, non-biomimetic approaches are needed [39]. repellence and the ability to resist even low surface energy liquids that would completely wet a typical superhydrophobic surface.…”

Durable, superoleophobic polymer–nanoparticle composite surfaces with re-entrant geometry via solvent-induced phase transformation

“… ( a ) θ flat angles of <90° on non–re-entrant and re-entrant geometries, liquid does not fully wet structure if θ flat + α ≥ 90° thanks to favorable shape of the liquid–vapor interface, ( b ) geometry with re-entrant curvature supporting a θ flat angle 70°, ( c ) geometry with re-entrant curvature supporting various θ flat angles of ≤90°, (d) re-entrant geometry supporting θ flat angles of 30°, and ( e ) doubly re-entrant geometry supporting θ flat angles of ≈0° 6 . …”

“…However, high droplet contact angles can still be achieved, even if the contact angle on the flat surface ( θ flat ) is low, through the use of re-entrant geometries, where surface asperities create an overhang 6 (i.e. become narrower closer to the surface), Fig.…”

Effect of nano-penning surface texturing on self-cleaning function

“…Amphiphobic properties are achievable by specific chemical composition and topography design, such as lowering surface free energies [3] [4][5] and designing functional surface textures [6] [7] [8].…”