Article

Petal Effect: A Superhydrophobic State with High Adhesive Force

Department of Chemistry, Tsinghua University, Beijing, P. R. China.
Langmuir (Impact Factor: 4.46). 05/2008; 24(8):4114-9. DOI: 10.1021/la703821h
Source: PubMed

ABSTRACT

Hierarchical micropapillae and nanofolds are known to exist on the petals' surfaces of red roses. These micro- and nanostructures provide a sufficient roughness for superhydrophobicity and yet at the same time a high adhesive force with water. A water droplet on the surface of the petal appears spherical in shape, which cannot roll off even when the petal is turned upside down. We define this phenomenon as the "petal effect" as compared with the popular "lotus effect". Artificial fabrication of biomimic polymer films, with well-defined nanoembossed structures obtained by duplicating the petal's surface, indicates that the superhydrophobic surface and the adhesive petal are in Cassie impregnating wetting state.

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    • "Since the " Lotus effect " has been observed and explained in late 1990s[5], more and more natural superhydrophobic surfaces are discovered and studied continually, such as Colocasia esculenta leaves[11], rice leaves[12], Canna indica seedpod[13], legs of water strider[14], legs of mosquito[15], duck feathers[16], butterfly wings[17], moth wings[18], termite wings[19], wings of cicada[20], mosquito compound eyes[21], etc. In addition to the above low adhesive superhydrophobicity, there are also some superhydrophobic surfaces with high adhesive ability, such as gecko feet[22], red rose petals[23], peanut leaves[24], etc. Recently, Salvinia molesta floating leaf has also been used as a model surface to show superhydrophobicity . "
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    ABSTRACT: The morphology and wettability of Water Bamboo Leaves (WBL) and their biomimetic replicas were investigated. The particular morphology structures of samples were characterized by Scanning Electron Microscopy (SEM) and Confocal Laser Scanning Microscopy (CLSM). The static wettability of samples was assessed by contact angle measurements, while the dynamic wettability was analyzed by high speed camera system. The wettability mechanism of WBL was also explained by Cassie model. Artificial surfaces were fabricated by duplicating WBL surface microstructures using PDMS in large area (5 cm (3 cm). The results show the main structure characteristics of this leaf surface are sub-millimeter groove arrays, micron-scale papillae and a superimposed layer with 3D epicuticular wax sculptures hierarchical structure, and the static Water Contact Angle (WCA) of 151°±2° and Water Sliding Angle (WSA) of 4°-6° indicate that WBL surface is superhydrophobic. The combination of wax film and microstructure of WBL surface gives its surface excellent superhydrophobic property. Complex hierarchical patterns with features from sub-millimeter to micron-scale range are well reproduced. The reason for the absence of nanostructures is melting of plant epidermal wax during the curing process. The WCA values on artificial WBL and negative PDMS replica are 146° ± 3° and 137° ± 2°, respectively, demonstrating preferable hydrophobicity. Differences in wetting behavior between natural leaves and artificial leaves originate from an inaccurate replication of the chemistry and structures of the three-dimensional wax projections on the leaf surface. Nevertheless, the morphological features of the leaf transferred to the replica improve significantly the hydrophobic properties of the replica when compared with the smooth PDMS reference. This study may provide an inspiration for the biomimetic design and construction of large area roughness-induced hydrophobic and anti-sticking material surface.
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    • "The novelty of the outcome may be caused by the unique wetting properties, whereby the hemolymph static contact angle was high but was associated with pinning when tilted. As such, the hemolymph impact outcomes may be more related to those for water on sticky superhydrophobic surfaces [32]. As noted above, once a hemolymph drop deposited on the different solid substrates, it remained adhered. "
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    • "In general, the adhesion with the water is so strong that the elastic papillae bend and swing back when the tips snap off the droplets [20]. The so-called Salvinia or petal effect [16] [17] [20] is therefore referred to super-hydrophobic adhesive surfaces with hydrophilic and hydrophobic hierarchical morphology providing sufficient roughness for exhibiting both a large contact angle and a high contact angle hysteresis, conversely to the lotus effect [2] [17] (high contact angle value and low contact angle hysteresis). Consequently, a water droplet on such a surface is nearly spherical in shape and cannot roll off even when the leaf is turned upside down. "
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