Petal Effect: A Superhydrophobic State with High Adhesive Force
Lin Feng,*,†Yanan Zhang,§Jinming Xi,|Ying Zhu,‡Nu ¨ Wang,‡Fan Xia,‡and Lei Jiang*,‡
Department of Chemistry, Tsinghua UniVersity, Beijing 100084, P. R. China, Institute of Chemistry,
Chinese Academy of Sciences, Beijing 100080, P. R. China, College of Chemistry, Jilin UniVersity,
Changchun 130023, P. R. China, and National Center for Nanoscience and Technology, Beijing 100080,
P. R. China
ReceiVed December 6, 2007. In Final Form: January 23, 2008
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.
The study of biological microstructures has been an active
so-called lotus effect. Water droplets do not stay stably on these
surfaces, where they can spontaneously roll off with a slight
tremble. During this process, dust particles on the surface are
but also very instructive for the design of new materials, where
a natural force might be used to clean a surface.
The self-cleaning phenomenon is usually explained as the
cooperation of rough surface with special micro- and nano-
structures and low surface energy materials, which lead to
than 150°) and a low sliding angle (less than 5°).2Up to now,
a variety of such surfaces have been theoretically studied and
also artificially prepared,7including films of carbon,8polymers,9-12
in wetting behavior. We have reported the preparation of
force mimicking gecko’s foot.18This material has been suc-
cessfully applied to no lost reversible transport of microliter-
Generally, there are two superhydrophobic states on a rough
a wet-contact mode of water and rough surface, where water
droplets pin the surface to form a high contact angle hysteresis.
The latter represents a nonwet-contact mode and water droplets
can roll off easily owing to the low contact angle hysteresis. We
recently clarified the definition of superhydrophobic surface as
five states, in which lotus and gecko attribute to the special case
in the nature, less examples are known showing the adhesive
property with an important Cassie impregnating wetting state.
Therefore, the study of the sixth superhydrophobic state in the
* Corresponding author. E-mail:
‡Chinese Academy of Sciences.
|National Center for Nanoscience and Technology.
(1) (a) Barthlott, W.; Neinhuis, C. Planta 1997, 202, 1. (b) Neinhuis, C.;
Barthlott, W. Ann. Bot. 1997, 79, 667.
(2) Feng, L.; Li, S.; Li, Y.; Li, H.; Zhang, L.; Zhai, J.; Song, Y.; Liu, B.; Jiang,
L.; Zhu, D. AdV. Mater. 2002, 14, 1857.
(3) Sun, T.; Feng, L.; Gao, X.; Jiang, L. Acc. Chem. Res. 2005, 38, 644.
C. R. Nature 2001, 414, 33.
(5) (a) Wagner, T.; Neinhuis, C.; Barthlott, W. Acta Zool. 1996, 77, 213. (b)
Gu, Z.; Uetsuka, H.; Takahashi, K.; Nakajima, R.; Onishi, H.; Fujishima, A.;
Sato, O. Angew. Chem., Int. Ed. 2004, 42, 894.
(6) Gao, X.; Jiang, L. Nature 2004, 432, 36.
(7) (a) Nosonovsky, M.; Bhushan, B. Nano Lett. 2007, 7, 2633. (b) Lee, Y.;
Park, S. H.; Kim, K. B.; Lee, J. K. AdV. Mater. 2007, 19, 2330. (c) Yu, Y.; Zhao,
Z. H.; Zheng, Q. S. Langmuir 2007, 23, 8212. (d) Nosonovsky, M. Langmuir
2007, 23, 3157.
(8) (a) Feng, L.; Yang, Z.; Zhai, J.; Song, Y.; Liu, B.; Ma, Y.; Yang, Z.; Jiang,
L.; Zhu, D. Angew. Chem., Int. Ed. 2003, 42, 4217. (b) Lau, K. K. S.; Bico, J.;
Teo, K. B. K.; Chhowalla, M.; Amaratunga, G. A. J.; Milne, W. I.; McKinley,
I. K. Carbon 2007, 45, 1702. (d) Li, Y.; Huang, X. J.; Heo, S. H.; Li, C. C.; Choi,
Y. K.; Cai, W. P.; Cho, S. O. Langmuir 2007, 23, 2169.
K.; Mayama, H.; Tsujii, K. Angew. Chem., Int. Ed. 2005, 44, 3453.
(10) (a) Erbil, H. Y.; Demirel, A. L.; Avci, Y.; Mert, O. Science 2003, 299,
1377. (b) Lu, X.; Zhang, C.; Han, Y. Macromol. Rapid Commun. 2004, 25, 1606.
23, 7263. (d) Michielsen, S.; Lee, H. J. Langmuir 2007, 23, 6004.
(11) (a) Feng, L.; Li, S.; Li, H.; Zhai, J.; Song, Y.; Jiang, L.; Zhu, D. Angew.
Chem., Int. Ed. 2002, 41, 1221. (b) Feng, L.; Song, Y.; Zhai, J.; Liu, B.; Xu, J.;
Jiang, L.; Zhu, D. Angew. Chem., Int. Ed. 2003, 42, 800. (c) Jiang, L.; Zhao, Y.;
Zhai, J. Angew. Chem., Int. Ed. 2004, 43, 4338.
(12) Ming, W.; Wu, D.; van Benthem, R.; de With, G. Nano Lett. 2005, 5,
(13) (a) Gao, L. Y.; Zheng, M. J.; Zhong, M.; Li, M.; Ma, L. Appl. Phys. Lett.
2004, 17, 1964. (c) Pan, Q. M.; Jin, H. Z.; Wang, H. Nanotechnology 2007, 18,
(14) (a) Bravo, J.; Zhai, L.; Wu, Z.; Cohen, R. E.; Rubner, M. F. Langmuir
2007, 23, 7293. (b) Lim, H. S.; Kwak, D.; Lee, D. Y.; Lee, S. G.; Cho, K. J. Am.
Chem. Soc. 2007, 129, 4128.
(15) Hosono, E.; Fujihara, S.; Honma, I.; Zhou, H. J. Am. Chem. Soc. 2005,
(16) Zhai, L.; Cebeci, F. C.; Cohen, R. E.; Rubner, M. F. Nano Lett. 2004,
(17) Fu ¨rstner, R.; Barthlott, W.; Neinhuis, C.; Walzel, P. Langmuir 2005, 21,
(18) Jin, M.; Feng, X.; Feng, L.; Sun, T.; Zhai, J.; Li, T.; Jiang, L. AdV. Mater.
2005, 17, 1977.
(19) Hong, X.; Gao, X.; Jiang, L. J. Am. Chem. Soc. 2007, 129, 1478.
(20) Wang, S.; Jiang, L. AdV. Mater. 2007, 19, 3423.
Langmuir 2008, 24, 4114-4119
10.1021/la703821h CCC: $40.75© 2008 American Chemical Society
Published on Web 03/01/2008
natural system is of significance not only for academic reasons
but also for their importance in practical applications.
Here, we disclose for the first time that there is a close array
of micropapillae on the surfaces of the petal of red rose (rosea
top. These hierarchical micro- and nanostructures provide
sufficient roughness for superhydrophobicity but have high
adhesive force with water. A water droplet on the surface of
these petala is sphere 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 familiar “lotus effect”.
Artificial fabrication of biomimic polymer films, with well-
impregnating wetting state. Note that much research has
previously been performed on the lotus leaf that tends to be in
Cassie’s state, whereas little has been studied on the Cassie
impregnating wetting state in the nature. Therefore, the finding
of petal effect should be of great biological and technological
grade reagents and were used without further purification. The
duplicated processing steps involved in the preparation of super-
hydrophobic adhesive surfaces are illustrated in the Supporting
Information (Figure S1). Poly(vinyl alcohol) (PVA, Mw) 22 000
g mol-1, ca. 10 wt %) water solution was poured onto the surface
of a red rose petal and exposed to air under ambient conditions.
When water was evaporated completely at room temperature, the
Polystyrene (PS, Mw) 100 000 g mol-1) films were then obtained
by pouring 15 wt % PS chloroform solution onto the prepared PVA
film, which were subsequently dried and peeled off.
Characterization. The morphological characterization of the
samples was examined by using scanning electronic microscope
(SEM). SEM measurements of the fresh petals were conducted on
angle system at ambient temperature. Water droplets (2.0 µL) were
dropped carefully onto the surface of samples. The average contact
angle was obtained by measuring at five different positions of the
Results and Discussion
Surface Morphology and Surface Wettability. Figure 1a
illustrates the typical scanning electronic micrograph of a usual
of micropapillae with an average diameter of 16 µm and height
of 7 µm. The magnified SEM image in Figure 1b clearly reveals
that these micropapillae exhibit cuticular folds in the nanometer
scale, about 730 nm in width on each top. It is known that the
hydrophobicity of a surface can be enhanced by being textured
with different scale structures. In nature, the surface of the lotus
leaf is famous for its self-cleaning property, which is induced
by the roughness at two length scales amplifying the intrinsic
hydrophobicity. Similar to this effect, the petal’s surface also
(Figure 1c) owing to its surface micro- and nanostructures.
However, the diverse design in the surface microstructures and
the different sizes of the lotus leaf and the red petal result in
different dynamic wetting. That is, water droplets with the same
volume can effortlessly roll off the surface of a lotus leaf, while
is facing up or even when it is turned upside down (Figure 1d),
Figure 1. (a, b) SEM images of the surface of a red rose petal, showing a periodic array of micropapillae and nanofolds on each papillae
top. (c) Shape of a water droplet on the petal’s surface, indicating its superhydrophobicity with a contact angle of 152.4°. (d) Shape of water
on the petal’s surface when it is turned upside down.
Superhydrophobic State with High AdhesiVe ForceLangmuir, Vol. 24, No. 8, 2008 4115
showing a high contact angle hysteresis. The crucial parameter
for this effect is the volume of the droplet. For a small droplet,
the weight is small compared to the surface tension force, and
thus it is expected that a droplet will stick to the surface. When
the volume of the water droplet is about 10 µL, a balance of the
will fall (for more details, see Supporting Information Figure
S2). This character imparts flowers special properties in that
small water droplets can stay stably on the petals maintaining
their fresh looking, while the bigger ones such as raindrops can
Duplication of Petal’s Surface. The surface microsructure
and surface property of natural petals provide us inspiration to
transfer process at room temperature. In a typical experiment,
of a fresh red rose petal and exposed to air under ambient
conditions. When water was evaporated completely at room
temperature, the PVA film could be peeled off, and it imprinted
the inverse petal’s surface microstructures. Subsequently, PS
film with the exact petal structure can be obtained by pouring
15 wt % PS chloroform solution onto the prepared PVA film,
allowing it to dry, and then peeling off. The SEM images of the
PVA and PS films are given in Figure 2. From panels a and b
of Figure 2, we can see that PVA film is characterized as the
inverse petal’s structures with a close-packed array of ap-
proximately hemispherical concaves and ditches in the middle
SEM images of the PS film, which was duplicated from the
textured PVA film. It is worth to note that the surface of the PS
film with a periodic array of embossment shows remarkable
microstructures and sizes similar to that of the original red rose
petal. This PS film with rough structure shows adhesive
superhydrophobicity with a contact angle of 154.6°, although
of about 95°.18Importantly, the duplicated PS film shows a high
contact angle hysteresis, i.e., a water droplet placed on the film
is tilted until turned upside down (insert in Figure 2d).
As previously reported, there are two possible origins for
superhydrophobicity: (1) the liquid attaches to the solid surface
state).21The Wenzel model describes homogeneous wetting by
where θwand θyare the Wenzel contact angle and the Young
contact angle, respectively and r is the roughness ratio, defined
as the ratio of the true area of surface to its projected area.
The Cassie model describes heterogeneous wetting by the
where θcand θyare the Cassie contact angle and the Young
contact angle, respectively, r is the ratio of the actual area to the
f is the area fraction of the projected wet area.
As for the details of contact angle hysteresis, Wenzel’s state
can induce a high contact angle hysteresis and Cassie’s state a
performed on these two states, especially on lotus leaf that tends
to exhibit Cassie’s state. However, considerably little has been
studied on another important superhydrophobic Cassie impreg-
of the solid are wetted with liquid and solid plateaus are dry.24
The Cassie impregnating wetting regime is described with
equations which are different from the Wenzel and Cassie ones.
(21) Callies, M.; Que ´re ´, D. Soft Matter 2005, 1, 55.
(22) Wenzel, R. N. Ind. Eng. Chem. 1936, 28, 988.
(23) Cassie, A. B. D.; Baxter, S. Trans. Faraday Soc. 1944, 40, 546.
(24) de Gennes, P. G.; Brochard-Wyart, F.; Que ´re ´, D. Capillarity and Wetting
Phenomena-Drops, Bubbles, Pearls, WaVes; Springer: New York, 2002; p 219.
Figure 2. (a, b) SEM images of the duplicated PVA film with inverse petal structures. (c, d) SEM images of the duplicated PS film with
the similar petal’s surface structures. (Inset in panel d is the shape of a water drop on the PS film when it is turned upside down, indicating
its superhydrophobic adhesive property.)
cos θw) r cos θy
cos θc) rf cos θy+ f - 1
4116 Langmuir, Vol. 24, No. 8, 2008 Feng et al.
In this regime, the liquid film impregnates the texture; however,
liquid film. On the basis of the hierarchical micro- and
both contact angles and adhesion are large is in the Cassie
impregnating wetting state (Figure 3).
This observation can be attributed to the difference of the
lotus leaf. For the low contact angle hysteresis, such as in the
lines on a randomly rough surface are expected to be contorted
microstructure spaces.25-28Thus, the droplet is constantly
advancing and receding at different contact line points, and it
and nanostructures are both larger than those of the lotus leaf.
water sealed in micropapillae would be clinged to the petal’s
surface, showing a high contact angle hysteresis in the range of
volume, when the surface is tilted to any angle or even turned
upside down. The adhesive property of petal provides us an
effective way to duplicate the surface microstructure. For
comparison, the same process was performed using a lotus leaf
as the template. Unfortunately, the prepared PVA film did not
exhibit the exact inverse microstructures of lotus leaf, that is,
only the top of each papilla was duplicated owing to the
nonwetting between lotus leaf and PVA water solution (see
Supporting Information Figure S3). Sun et al.30have previously
reported on how to create a superhydrophobic surface using a
an inspiration for the preparation of biomimic polymer films,
Other Petals. The microstructures and the special superhy-
drophobicity with a high contact angle hysteresis can also be
found on other flower petals due to their periodic array of
microsturctures. As a typical example, panels a and b of Figure
lily, which is characterized as close-packed hexagons with an
hexagon. The SEM image of the PVA film duplicated from the
petal of Chinese Kafir lily is shown in Figure 4c, while that of
with a large contact angle and a high contact angle hysteresis
(inset in Figure 4d). In another example, the sunflower petal
of 15 µm and a helix width of 2.5 µm on each line, (Figure 4e,f).
Panels g and h of Figure 4 show the SEM images of the
petal and the prepared PVA film. The PS film has the
(25) (a) O ¨ner, D.; McCarthy, T. J. Langmuir 2000, 16, 7777. (b) Chen, W.;
1999, 15, 3395.
(26) Li, S.; Li, H.; Wang, X.; Song, Y.; Liu, Y.; Jiang, L.; Zhu, D. J. Phys.
Chem. B 2002, 106, 9274.
(27) Yoshimitsu, Z.; Nakajima, A.; Watanabe, T.; Hashimoto, K. Langmuir
2002, 18, 5818.
(28) Extrand, C. W. Langmuir 2002, 18, 7991.
(29) (a) Herminghaus, S.; Europhys. Lett. 2000, 52, 165. (b) Bormashenko,
E.; Stein, T.; Whyman, G.; Bormashenko, Y.; Pogreb, R. Langmuir 2006, 22,
9982. (c) Marmur, A. Langmuir 2003, 19, 8343.
(30) Sun, M.; Luo, C.; Xu, L.; Ji, H.; Ouyang, Q.; Yu, D.; Chen, Y. Langmuir
2005, 21, 8978.
Figure 3. Schematic illustrations of a drop of water in contact with the petal of a red rose (the Cassie impregnating wetting state) and a
lotus leaf (the Cassie’s state).
Superhydrophobic State with High AdhesiVe ForceLangmuir, Vol. 24, No. 8, 2008 4117
on the upside down PS film). We propose that these wetting
of the duplicated technique used herein, polymer films with
a duplication process can be applied to different polymer
polyvinyl chloride, polydimethylsiloxane, polymethyl meth-
acrylate, polyesters, and polyamides.
In conclusion, the understanding of the petal effect provides
us with an example of the nature of a superhydrophobic surface
with a high adhesive force to water, which shows a unusual
Cassie impregnating wetting state. The observation of the petal
Figure 4. (a, b) SEM images of the surface of a Chinese Kafir lily petal, showing a periodic array composed of close-packed hexagons
and strips in two scales. (c, d) SEM images of the duplicated PVA and PS films from Chinese Kafir lily petal (inset image is the shape of
a water droplet on the upside down PS film). (e, f) SEM images of the surface of a sunflower petal, showing a periodic array composed
of parallel lines and helices in two scales. (g, h) SEM images of the duplicated PVA and PS films from the sunflower petal (inset image
is the shape of a water droplet on the upside down PS film).
4118 Langmuir, Vol. 24, No. 8, 2008Feng et al.
biomimic polymer films that possesses both the superhydro-
This study not only improves our understanding of the self-
insights into the design of new materials for applications in
coatings, functional fibers, and decoration. Material fabrication
using the natural petals, an environment friendly material, as
templates has the obvious merit over many other conventional
techniques, which are not accessible for this purpose.
Acknowledgment. The authors thank the project funded by
the National Nature Science Foundation of China (50703020),
Tsinghua Basic Research Foundation (JCpy2005059), and
Foundation for the Author of National Excellent Doctoral
Dissertation of P. R. China (200526) for continuing financial
support. Thanks to Professor Xi Zhang and Professor Lei Liu
(Tsinghua University) for the helpful discussions.
Supporting Information Available: The preparation process
of polymer films, shapes of water droplets with different volumes on
the surface of red rose petal, and SEM images of the surface of a lotus
leaf and the PVA film duplicated from a lotus leaf. This material is
available free of charge via the Internet at http://pubs.acs.org.
Superhydrophobic State with High AdhesiVe Force Langmuir, Vol. 24, No. 8, 2008 4119