Petal effect: A superhydrophobic state with high adhesive force

Department of Chemistry, Tsinghua University, Beijing, P. R. China.
Langmuir (Impact Factor: 4.38). 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.

  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we report novel superhydrophobic surfaces with tunable water adhesion by combining mussel-inspired surface chemistry and bioinspired multiscale surface structures. Highly ordered honeycomb porous films were prepared from a diblock copolymer polystyrene-block-poly(N,N-dimethylaminoethyl methacrylate) by the breath figure method. Removing the top surface layer of the honeycomb films leads to pincushion-like surfaces. The films were coated with polydopamine after completely prewetting by ethanol, followed by the reaction with 1H,1H,2H,2H-perfluorodecanethiol for fluorination. As a result of the surface modification, both the honeycomb and the pincushion-like surfaces are superhydrophobic with a water contact angle higher than 150°. Interestingly, the former is highly adhesive, on which water droplets are pinned at any tilted angles, whereas the latter is relatively low adhesive. Calculations indicate that the honeycomb films are in the Cassie state, whereas the pincushion-like surfaces are in the metastable Cassie state. On the basis of these superhydrophobic surfaces with different adhesive properties, no-loss transportation of water droplets has been demonstrated.
    The Journal of Physical Chemistry C 02/2015; 119(7). DOI:10.1021/jp513001k · 4.84 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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 · 3.67 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A hierarchical structure is an assembly with a multi-scale morphology and with a large and accessible surface area. Recent advances in nanomaterial science have made increasingly possible the design of hierarchical surfaces with specific and tunable properties. Here, we report the fractal analysis of hierarchical single-walled carbon nanotube (SWCNT) films realized by a simple, rapid, reproducible, and inexpensive filtration process from an aqueous dispersion, then deposited by drytransfer printing method on several substrates, at room temperature. Furthermore, by varying the thickness of carbon nanotube random networks, it is possible tailoring their wettability due to capillary phenomena in the porous films. Moreover, in order to describe the wetting properties of such surfaces, we introduce a two-dimensional extension of the Wenzel-Cassie-Baxter theory. The hierarchical surface roughness of SWCNT coatings coupled with their exceptional and tunable optical and electrical properties provide an ideal hydrophobic composite surface for a new class of optoelectronic and nanofluidic devices.
    Scientific Reports 02/2015; 5(8583). DOI:10.1038/srep08583 · 5.08 Impact Factor