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


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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    • "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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    ABSTRACT: Insect fouling from coagulated hemolymph and exoskeleton parts is a major challenge in the aerospace industry for the next generation of aerodynamic surfaces, which will employ laminar flow that requires extremely smooth surfaces. However, the wetting physics and dynamics of hemolymph (insect blood) on surfaces are not well understood. The present study seeks to gain a fundamental insight on the effect of surface wetting characteristics and dynamics resulting from a hemolymph drop impact, the first such study. In particular, hemolymph drops extracted from Acheta domesticus were dispensed from a range of heights to vary the kinetic impact on surfaces, which had widely varying water wetting behavior (from superhydrophilic to superhydrophobic). The impact dynamics were investigated with high-speed imaging while the dried residues were studied with optical microscopy. It was found that a superhydrophobic surface (based on thermoplastic with silica nano-particles) was able to significantly reduce hemolymph drop spreading, and even provide complete rebound when impacting on inclined surfaces.
    Applied Surface Science 08/2015; 345:36-43. DOI:10.1016/j.apsusc.2015.02.185 · 2.71 Impact Factor
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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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    ABSTRACT: We have taken advantage of the native surface roughness and the iron content of AISI 316 stainless steel to directly grow multi-walled carbon nanotube (MWCNT) random networks by chemical vapor deposition (CVD) at low-temperature ([Formula: see text]) without the addition of any external catalysts or time-consuming pre-treatments. In this way, super-hydrophobic MWCNT films on stainless steel sheets were obtained, exhibiting high contact angle values ([Formula: see text]) and high adhesion force (high contact angle hysteresis). Furthermore, the investigation of MWCNT films with scanning electron microscopy (SEM) reveals a two-fold hierarchical morphology of the MWCNT random networks made of hydrophilic carbonaceous nanostructures on the tip of hydrophobic MWCNTs. Owing to the Salvinia effect, the hydrophobic and hydrophilic composite surface of the MWCNT films supplies a stationary super-hydrophobic coating for conductive stainless steel. This biomimetical inspired surface not only may prevent corrosion and fouling, but also could provide low friction and drag reduction.
    Nanotechnology 03/2015; 26(14):145701. DOI:10.1088/0957-4484/26/14/145701 · 3.82 Impact Factor
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    • "Another reason is that the influence was caused by the surface morphology and the EGC-1720 coating layer. Related studies [3] [4] [19] [36] [37] have indicated that hydrophobicity does not equal lower droplet contact angle hysteresis (CAH), and vice versa. However, the condensation mode was still DWC. "
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    ABSTRACT: Superhydrophobic surface modification is applied to a monolithic copper heat sink. A monolithic copper heat sink is used to prevent contact thermal resistance. EGC-1720 fluorosilane polymer is employed as the waterproof agent. Durability of the EGC-1720 coated surface is investigated. The relative heat transfer enhancement of the heat sink is compared. a b s t r a c t In this study, the condensation heat transfer performance on a pure copper surface, as well as a superhydrophobic-modified copper surface were compared. Differing from other condensation heat transfer experimental designs, a monolithic copper heat sink was utilized in this study to prevent contact thermal resistance and/or thermal conduction limitation of the thermal paste applied between the modified condensation surface and heat sink plate. This approach has not yet been documented in the literature. The superhydrophobic copper heat sink surface was prepared using a hydrogen peroxide immersion and fluorosilane polymer (EGC-1720) spin-coating. Experimental results show that the condensation heat transfer performance on the superhydrophobic copper surface is superior to that of a pure copper surface. Additionally, durability tests of the pure and superhydrophobic coating copper surfaces in a harsh vapor environment are discussed in this study.
    Applied Thermal Engineering 10/2014; 75:908-917. DOI:10.1016/j.applthermaleng.2014.10.019 · 2.74 Impact Factor
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