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Fig. 9.7 Nepenthes pitcher plant: on the left, folded leaves that create pitcher traps (Copyright
2013 Alessandro Pelizzi). On the right, Nepenthes pitcher and peristome morphology
highlighting the porous cross-sectional structure and the two levels of ridges (Adapted with
permission from Bohn and Federle
2004
; Copyright 2004 National Academy of Sciences,
U.S.A.)
overlapping the adjacent cell, so that the surface contains a series of steps toward
the pitcher inside and is anisotropic. In some species, this surface is covered with
wax; still, the actual trapping mechanism is based on the formation of a layer of
water on top, owing to the presence of hygroscopic nectar—in fact, their trapping
ability is boosted in rainy days. Surface wettability is anisotropic, following ridges
direction (Bohn and Federle
2004
; Bauer et al.
2009
).
This peculiar structuring has recently become focus of several research studies
dedicated to the production of slippery surfaces, with applications in the field of
self-cleaning, anti-icing, antifouling, and fluid transport (Lafuma and Quéré
2011
;
Kim et al.
2012b
; Epstein et al.
2012
). The first biomimicking of pitcher plants was
proposed by Wong et al. (
2011
), who labeled their newly developed system as
SLIPS—slippery liquid infused porous surface. SLIPS are based on micro-nano-
structured porous surfaces that are infused with lubricating liquids, which induce a
superhydrophobic character until the lubricant stably wets the surface: currently,
the major issue of such self-cleaning and anti-icing mechanism is indeed the effect
durability (Rykaczewski et al.
2013
).
9.2.3 Hydrophilic and Superoleophobic Plants and Animals
Pitcher plants are just the first example of natural systems used as reference in
biomimetic self-cleaning materials. Several systems take inspiration from hydro-
philic surfaces, with different mechanisms. Recent investigations on some mi-
crostructured surfaces, such as snail shells (Fig.
9.8
a), brought to light a peculiar
superoleophobic behavior that induces extraordinary self-cleaning performances:
also in this case, the presence of water is crucial for the mechanism to work.
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