Haoshen Zhou talks with
ScienceWatch.com and answers a few questions about
this month's Fast Moving Front in the field of Materials
Article: Superhydrophobic perpendicular nanopin
film by the bottom-up process
Authors: Hosono, E;Fujihara, S;Honma,
Journal: J AM CHEM SOC, 127 (39): 13458-13459 OCT 5
Addresses: Natl Inst Adv Ind Sci & Technol, Umezono
1-1-1, Tsukuba, Ibaraki 3058568, Japan.
Natl Inst Adv Ind Sci; Technol, Tsukuba, Ibaraki 3058568,
Keio Univ, Kohoku Ku, Yokohama, Kanagawa 2238522, Japan.
Why do you think your paper is highly
Generally, the superhydrophobic surface was prepared by application of a
rough surface based on nano- or macro-structures coated with the
low-surface molecular energy molecular compound fluoroalkyltrimethoxysilane
(FAS). These low-surface energy molecules such as FAS still have a
hydrophobic surface with contact angle of water (CAW) in the range from
100o-108o. The traditional method is merely to
increase the CAW from hydrophobic (CAW: 90o-120o)
into the superhydrophobic range (CAW: 150o-180o).
It remains a challenge to increase the CAW from hydrophilic into
superhydrophobic range, although it looks possible, according to Cassie's
law, which explains how simply roughing up a surface increases the apparent
surface angle. This paper achieved this result based on controlling the
surface fraction ratio vs. the trapped air by using a perpendicular nanopin
film with a pin diameter of 6.5nm by using the chemical-bath deposition
(CBD) method. The CAW was increased from about 75o to
178o, which is nearly an ideal super-hydrophobic surface. It
appears that this method should provide the possibility to design
superhydrophobic surfaces from low-CAW materials. Such inorganic materials
with low CAW will be interesting, not only for chemical and physical
fundamental research, but also for industrial applications.
Does it describe a new discovery, methodology, or
synthesis of knowledge?
"Some other possible
applications—such as LIB, SP, PEFC,
DSSC, OWGS—are already being
investigated by our group for solutions to
the worldwide problems involving energy and
It is the first time a hydrophilic surface with a CAW of 75o was
transformed into a superhydrophobic surface with a CAW of 178o,
while only utilizing a perpendicular nanopin structure film.
Would you summarize the significance of your paper
in layman's terms?
The hydrophilic surface can be changed into superhydrophobic only by
modifying the roughness of the surface.
How did you become involved in this research and
were there any particular problems encountered along the way?
In our group, we synthesize various nanostructure functional materials in
order to develop energy storage devices and environmental detectors, such
as the lithium ion battery (LIB), super-capacitor (SP), polymer electrolyte
fuel cell (PEFC), dye sensitized solar cell (DSSC), and optical waveguide
gas sensor (OWGS).
At first, we developed a bottom-up approach to synthesize cobalt hydroxide
nanosheets and nanopins under different processing conditions. At that
time, we wanted to intercalate some molecular substances such as lauric
acid into crystalline frame of d-spacing in order to fabricate
organic/inorganic hybrid materials. In fact, we failed.
However, as we discovered the super-hydrophobic phenomenon purely by
accident, we realized that this interesting phenomenon could be completely
explained by Cassie's law and extended a new output for perpendicular
nanopin films. As for practical applications, there are still some critical
problems remaining, such as how to increase its mechanical strength.
Where do you see your research leading in the
We have extended the nanopin-to-nanosheet and nanorod structures for
super-hydrophobic surfaces, and cobalt hydroxide to other metal hydroxide
or metal oxides. In the future, the concept described in this paper can be
extended to cover several potential practical applications such as
anti-sticking, anti-frost, anti-cloudy, anti-contamination, anti-snow
stacking, self-cleaning, and minimizing flow resistance through a pipeline.
Do you foresee any social or political implications
for your research?
Currently, nanostructure surface modification has become one of the most
efficient ways to fabricate functional surfaces for various applications.
Super-hydrophobic technology is only one example.
Some other possible applications—such as LIB, SP, PEFC, DSSC,
OWGS—are already being investigated by our group for solutions to the
worldwide problems involving energy and the environment. Some of these
investigations are being funded by the Japan Science and Technology Agency
(JST), New Energy and Industrial Technology Development Organization
(NEDO), and the Japan Society for the Promotion of Science (JSPS) and the
National Institute of Advanced Industrial Science and Technology (AIST).
Haoshen Zhou, Ph.D.
Group Leader and Chief Researcher
Energy Interface Technology Research Group
Energy Technology Research Institute
National Institute of Advanced Industrial Science and Technology
Keywords: superhydrophobic surfaces,
fluoroalkyltrimethoxysilane, hydrophobic surface with contact angle of
water, chemical-bath deposition method, perpendicular nanopin structure
film, synthesize various nanostructure functional materials, cobalt
hydroxide nanosheets and nanopins, Cassie's law.