Coatings able to repel liquids are a promising way to improve a wide variety of materials, from biomedical devices to self-cleaning structures, and considerable research has been dedicated to mimicking the lotus leaf — an excellent non-wetting material. But such surfaces, patterned with a regular texture on top of which water droplets sit without wetting it, do not efficiently repel organic liquids. Now, mimicking the leaves of the carnivorous pitcher plant instead, Joanna Aizenberg at the University of Harvard and co-workers have prepared very slippery omniphobic surfaces, which repel both aqueous and organic liquids.
A porous material with a micro- or nanotexture that is not necessarily regular, in this case made of either polyfluoroalkyl silane or Teflon, is first impregnated with a lubricating liquid. The lubricant chosen, a perfluorinated oil that is immiscible with both aqueous and organic liquids, fills the material's microstructure — adhering to it sufficiently so as not to be displaced at a later stage by the liquid to be repelled — and forms a continuous film on the surface.
The resulting lubricant coating creates a smooth surface with very low friction, making for an efficient repellent against a variety of aqueous and organic liquids, even blood and crude oil. Furthermore, it is not affected by ice, and can self-heal — areas that have been physically damaged (for example by abrasion) are refilled as long as the lubricant is present within the porous substrate. The slippery liquid-infused porous surfaces, as Aizenberg and colleagues call them, are also efficient even under high pressure, and judicious choice of the substrate and lubricant leads to an omniphobic material that is optically transparent.
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Pichon, A. Pitcher plant perfect. Nature Chem 3, 834 (2011). https://doi.org/10.1038/nchem.1190