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Fabrication of a Superamphiphilic SS-400 Oil Separator Surface Using a Ag-Doped ZnO Nanorod Coating

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A simple fabrication technique is described for preparing Ag-doped ZnO nanorods using a rapid hydrothermal technique to create a superamphiphilic surface on SS-400 substrates. The high roughness resulting from Ag-doped ZnO nanorod surfaces is responsible for generating the superamphiphilic property of the SS-400 substrate. The fabricated surface shows contact angles (CAs) of almost 0° for water and olive oil, resulting in complete spreading of water and oily liquids. The fabricated surface also exhibits excellent superamphiphilic properties after long-term storage, thermal, and mechanical testing. However, after modification with a lowsurface-energy material (stearic acid), the fabricated surface exhibits superhydrophobic properties with water CAs of 158° and sliding angles (SAs) of less than 5°. We also applied our fabrication method to a helical-type oil separator. The oil separator, when treated with Ag-doped ZnO nanorods with a superamphiphilic surface, improved its oil separation efficiency and pressure drop compared with those of a commercial oil separator. Thus, our surface fabrication technique can be implemented easily to large-area, three-dimensional surfaces. Due to their ease and rapidity of manufacture and long-term wetting stability, these surfaces are potentially suitable for large-scale industrial applications in a variety of fields.
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ARTICLE
Copyright © 2016 by American Scientific Publishers
All rights reserved.
Printed in the United States of America
Science of
Advanced Materials
Vol. 8, pp. 1595–1602, 2016
www.aspbs.com/sam
Fabrication of a Superamphiphilic SS-400 Oil
Separator Surface Using a Ag-Doped ZnO
Nanorod Coating
Sumit Barthwal1,YuraKim
2, Joon Ahn3, and Si-Hyung Lim3,
1Department of Bio and Nano Chemistry, Kookmin University, Seoul 136-702, South Korea
2Department of Mechanics and Design, Kookmin University, Seoul 136-702, South Korea
3School of Mechanical Systems Engineering, Kookmin University, Seoul 136-702, South Korea
ABSTRACT
A simple fabrication technique is described for preparing Ag-doped ZnO nanorods using a rapid hydrother-
mal technique to create a superamphiphilic surface on SS-400 substrates. The high roughness resulting from
Ag-doped ZnO nanorod surfaces is responsible for generating the superamphiphilic property of the SS-400
substrate. The fabricated surface shows contact angles (CAs) of almost 0for water and olive oil, resulting in
complete spreading of water and oily liquids. The fabricated surface also exhibits excellent superamphiphilic
properties after long-term storage, thermal, and mechanical testing. However, after modification with a low-
surface-energy material (stearic acid), the fabricated surface exhibits superhydrophobic properties with water
CAs of 158and sliding angles (SAs) of less than 5. We also applied our fabrication method to a helical-type
oil separator. The oil separator, when treated with Ag-doped ZnO nanorods with a superamphiphilic surface,
improved its oil separation efficiency and pressure drop compared with those of a commercial oil separator.
Thus, our surface fabrication technique can be implemented easily to large-area, three-dimensional surfaces.
Due to their ease and rapidity of manufacture and long-term wetting stability, these surfaces are potentially
suitable for large-scale industrial applications in a variety of fields.
KEYWORDS: Superamphiphilic, SS-400, Ag-Doped ZnO, Contact Angle, Oil-Separator.
1. INTRODUCTION
Surface wettability is of great concern in both academic
study and practical use. The control of surface wetta-
bility is an emerging field of study. Surface wettability
is governed by both chemical composition and surface
morphology, and is characterized in terms of water con-
tact angle (WCA). If a surface has a CA larger than
90, it is hydrophobic, whereas if its CA is under 90,
then it is hydrophilic. In recent years, inspired by nature,
many research groups have focused on the fabrication of
superhydrophobic surfaces owing to their wide range of
possible applications. Researchers have fabricated artifi-
cial superhydrophobic surfaces having micro- or nano-
structures using a variety of methods, including etching
techniques,1–4 a sol–gel process,5electrospinning,6depo-
sition of nanoparticles on smooth or rough substrates,7
growth of nanotubes,8electrochemical anodization,9and
laser fabrication.10
Author to whom correspondence should be addressed.
Email: shlim@kookmin.ac.kr
Received: 24 December 2015
Accepted: 28 February 2016
However, in comparison to the number of studies con-
ducted on superhydrophobic properties, those reported
on superhydrophilic surfaces have been few. Recently,
however, superhydrophilic surfaces have attracted inter-
est owing to their broad range of applications, includ-
ing self-cleaning, ultrafast drying, antifogging surfaces,11
heat transfer,12 water harvesting,1314 and biomedical
applications.15
Generally, two approaches lead to superhydrophilicity.
The first is to apply light-sensitive materials to develop
superhydrophilic surfaces. When a photo-induced mate-
rial is exposed to UV light, the surface changes from
hydrophilic to superhydrophilic. Fujishima et al.16 first
reported the photo-induced superhydrophilicity of TiO2
surfaces. When a TiO2surface is illuminated by UV light,
the surface turns from slightly hydrophilic to superhy-
drophilic. TiO2and various other metal oxides such as
SnO2,WO
3,ZnO,andV
2O5are known to exhibit photo-
induced superhydrophilicity. Another approach for form-
ing a stable superhydrophilic surface is to create a rough
texture on surfaces using the proper chemistry. Surface
roughness plays a key role in wetting. The mechanism
Sci. Adv. Mater. 2016, Vol. 8, No. 8 1947-2935/2016/8/1595/008 doi:10.1166/sam.2016.2774 1595
Fabrication of a Superamphiphilic SS-400 Oil Separator Surface Using a Ag-Doped ZnO Nanorod Coating Barthwal et al.
ARTICLE
behind rough-surface-driven superhydrophilicity involves
the penetration of water into the cracks and grooves
generated because of the rough surface, which leads to
complete wetting. Surface wetting can be easily manip-
ulated by changing surface roughness or porosity. There
are various techniques for imparting roughness that result
in the fabrication of artificial superhydrophilic surfaces
such as etching,17 the sol–gel method,1819 layer-by-layer
assembly,2021 hydrothermal treatment,22–24 etc. Recently,
some groups have demonstrated the fabrication of super-
hydrophilic surfaces using rough surfaces. Cebeci et al.
created a nanoporous thin film using layer-by-layer assem-
bly of silica nanoparticles and a polycation to achieve
superhydrophilicity.20 This superhydrophilic behavior is
attributed to the rapid penetration of water into the 3D
nanoporous network. The concentration of the solution,
pH, and particle size were found to greatly influence film
properties. Masuda et al.25 recently fabricated SnO2films
on fluorine-doped tin oxide (FTO) substrates in aqueous
solutions. These films, about 800 nm in thickness, grew
in the solutions. They consisted of nanosheets of about
5–10 nm in thickness and about 100–1600 nm in plane
size. Smaller nanosheets formed dense structures in the
bottom area, whereas larger nanosheets formed porous
structures in the surface area of the films. The fabricated
nanosheet-assembly structure of SnO2films have played a
key role in achieving superhydrophilic surfaces with static
contact angles below 1.
SS-400 is one of the most commonly used hot-rolled
structural steels; it comes in the form of plates, sheets, and
strips for general structural applications. As per Japanese
Industrial Standard (JIS) G 3101, SS-400 material has
no chemical composition assigned. The percentages of
carbon, silicon, and manganese are not fixed, but the
phosphorus and sulphur concentrations are constrained to
maximum levels below 0.05%, and the remaining com-
ponent is iron with negligible impurities. This material is
cheap, excellent in terms of weldability and machinabil-
ity, and is widely used in building ships, bridges, struc-
tural tubes, pipes, rods, and various structural sectional
steels. Because of the great demand for SS-400 substrates
owing to their direct practical and industrial applications,
it is highly desirable to fabricate superamphiphilic SS-400
substrates.
In this work, we focus on developing a simple and
low-cost method to achieve a superamphiphilic surface
on a SS-400 substrate, aiming to have excellent long-
term stability, large-scale processing, thermal stability, and
mechanical durability. In this study, ZnO nanorods doped
with Ag were synthesized using a rapid hydrothermal
technique to create superhydrophilic surfaces on SS-400
substrates. The fabricated SS-400 substrates induce com-
plete spreading of water and olive oil, leading to a con-
tact angle of almost 0. The entire procedure was very
easy to operate and no special techniques or sophisti-
cated equipment are required. Moreover, the procedure
is time-saving and inexpensive. The fabricated Ag-doped
ZnO nanorods also exhibited long-term stability, good
thermal stability, and mechanical durability. Finally, we
also applied our fabrication method to a large, three-
dimensional, curved oil separator made of SS-400 surfaces
to achieve a superamphiphilic SS-400 surface. The exper-
imental result showed a higher oil separation efficiency by
up to 91.2% with a low pressure drop in comparison with
a commercial oil separator. Hence, we expect that this sim-
ple fabrication technique will create a new opportunity for
the production of large-scale three-dimensional or curved
superamphiphilic engineering materials for many industrial
applications as well as for basic research.
2. EXPERIMENTAL SECTION
Zinc nitrate hexahydrate, silver nitrate, and ammonia solu-
tion were purchased from Alfa Aesar Inc. All other chemi-
cals were of analytical grade and were used without further
purification. SS-400 plates were purchased locally and cut
into small pieces.
In a typical procedure, 0.1 M zinc nitrate and 0.002 M
silver nitrate were first dissolved into 100 mL of deion-
ized (DI) water. An ammonia solution (29.6%) was added
until the solution became transparent. Later, the SS-400
substrates were ultrasonically cleaned in acetone and
deionized water (DI) for 5 min and then dried in a stream
of nitrogen. The clean SS-400 substrate was immersed ver-
tically into the above solution and the beakers were placed
inside a preheated oven for 1 hour at 95 C. Finally, after
the reaction was completed, the substrate was rinsed in DI
water and dried with N2gas.
2.1. Characterization
The morphology of all the samples prepared in the present
study was examined using field-emission scanning elec-
tron microscopy (FESEM, JEOL, JSM-740 1F, Japan).
The CAs were measured with 5 L droplets of water
and olive oil using a CA measurement system (Phoenix
300 Touch, SEO Co. Ltd). The average CA values were
obtained by measuring each sample at a minimum of five
different positions at room temperature. Optical images
of the droplets were obtained using a digital camera
(SONY Inc.).
3. RESULTS AND DISCUSSION
SEM was used to examine surface morphology. Typi-
cal SEM images of the as-synthesized Ag-doped ZnO
nanorods are shown in Figure 1. The result indicates that
highly dense Ag-doped ZnO nanorods were grown on the
SS-400 substrate. The Ag-doped ZnO nanorods were less
than about 1.5 m in length with an average diameter
of 300 nm. The composition of the as-synthesized Ag-
doped ZnO nanorods was further characterized by EDX
and results are shown in Figure 1(d). All the peaks clearly
1596 Sci. Adv. Mater., 8, 1595–1602, 2016
Barthwal et al. Fabrication of a Superamphiphilic SS-400 Oil Separator Surface Using a Ag-Doped ZnO Nanorod Coating
ARTICLE
Fig. 1. SEM images of the Ag-doped ZnO nanorods observed at (a) low and (b–c) high magnification, and (d) EDX spectrum.
imply that the as-synthesized nanorods consisted of the
elements Zn, Ag, and O with some additional peaks. These
additional peaks belong to the SS-400 substrate.
The wetting behaviour of the as-synthesized surface was
determined by contact angle (CA) measurement. As can
be seen in Figure 2, the water and olive oil CAs for
a bare SS-400 surface were 40and 28, respectively,
showing amphiphilic properties since CA <90.How-
ever, after modifying the SS-400 substrate with Ag-doped
ZnO nanorods, the amphiphilic property of the surface
improved, with a decrease in CAs to 0for both water and
olive oil. It is known that the increase in surface roughness
plays an important role in improving wettability. Accord-
ing to Wenzel’s theory,26 the apparent contact angle aof
a liquid droplet placed on a rough solid surface is given
by the following equation:
cos a=rcos
where ris the roughness factor and is the equilibrium
CA of the liquid on a smooth surface of the same material.
Real surfaces always possess a certain degree of rough-
ness, and hydrophilic materials have <90for water.
As a result, the apparent CA of a hydrophilic surface
decreases with increasing roughness. In the case of the fab-
ricated SS-400 substrate, the surface is very rough because
of the Ag-doped ZnO nanorods. Many nanorods are com-
bined and aggregate into 3D architectures. Thus, when a
water droplet comes into contact with such surfaces, it can
be induced by the capillary effects of the three-dimensional
surface shape to enter into and fill the grooves of the film,
spreading instantly.
We examined the thermal stability of the fabricated Ag-
doped ZnO nanorod surfaces. The fabricated SS-400 sub-
strate was heated at different temperatures for 30 min
in the ambient environment. Then, the superamphiphilic
property of the heated surfaces was checked by mea-
suring the CAs with water and olive oil. As shown in
Figure 3, there was no evident change in the olive oil CA
values on the fabricated SS-400 substrate modified with
Ag-doped ZnO nanorods, and the surfaces still showed
excellent superoleophilic properties. The fabricated super-
amphiphilic surfaces had many practical and industrial
applications. However, these fabricated surfaces should
have long-term stable superamphiphilic property after pro-
longed exposure to the ambient environment, so these fab-
ricated superamphiphilic surfaces can be applied to real,
practical applications. Hence, we investigated the stabil-
ity of the superamphiphilicity of the fabricated Ag-doped
ZnO nanorod surfaces on the SS-400 substrates after expo-
sure in air for various periods of time. The results indicate
that even after 8 weeks of storage, the fabricated SS-400
substrate was able to retain its superamphiphilic proper-
ties such that water and olive oil droplets spread on the
surfaces with CAs of less than 5. Figure 4 shows the rela-
tionship between the olive oil CA on the fabricated SS-400
surfaces and the exposure time. Thus, we conclude that
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Fabrication of a Superamphiphilic SS-400 Oil Separator Surface Using a Ag-Doped ZnO Nanorod Coating Barthwal et al.
ARTICLE
Fig. 2. Contact angle profile of untreated bare SS-400 surface with (a) water and (b) olive oil; SS-400 surface modified with Ag-doped ZnO nanorods
with (c) water and (d) olive oil.
fabricated Ag-doped ZnO nanorod rough surfaces on SS-
400 substrate are sufficiently stable after exposure to envi-
ronmental conditions; moreover, they enable spreading of
liquids easily with excellent superamphiphilic properties.
We also tested the mechanical durability of the fabricated
SS-400 substrates by applying different loads for 20 min.
As shown in Figure 5, we applied a load of up to 4 N on
the fabricated surfaces (the loaded area was approximately
5cm
2. The result indicates that Ag-doped ZnO nanorod
Fig. 3. The relationship between temperature and olive oil CA on fab-
ricated Ag-doped ZnO nanorods on an SS-400 substrate.
surfaces on SS-400 substrates retain their superamphiphilic
properties after applying different loads.
A textured superhydrophilic surface can become a
superhydrophobic surface if it is chemically modified with
low-surface-energy materials. Therefore, untreated bare
SS-400 and fabricated SS-400 superamphiphilic samples
were modified with 5 mM of stearic acid in ethanol. The
fabricated substrates were immersed in the stearic acid
Fig. 4. Long-term stability of the fabricated SS-400 substrates with
varying storage duration. The inset shows the olive oil drop spreading on
the surfaces on the fabrication day and after exposure in air for 8 weeks.
1598 Sci. Adv. Mater., 8, 1595–1602, 2016
Barthwal et al. Fabrication of a Superamphiphilic SS-400 Oil Separator Surface Using a Ag-Doped ZnO Nanorod Coating
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Fig. 5. Contact angle of olive oil on the fabricated Ag-doped ZnO nanorod surface on SS-400 substrate after applying different forces.
Fig. 6. Contact angle profile of water on the SS-400 substrate: (a) Bare surface after modification with stearic acid; (b) Ag-doped ZnO nanorods
fabricated on an SS-400 substrate after treatment with stearic acid; (c) sliding angle on the fabricated surface; and (d) photograph of water dropletson
the fabricated surface.
Fig. 7. Photograph and cross-sectional view of different liquid droplets on the fabricated superamphiphobic SS-400 substrate.
Sci. Adv. Mater., 8, 1595–1602, 2016 1599
Fabrication of a Superamphiphilic SS-400 Oil Separator Surface Using a Ag-Doped ZnO Nanorod Coating Barthwal et al.
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Tab l e I . Surface contact angles and sliding angles (SAs) of various
liquids of different surface tensions on the fabricated SS-400 substrates
modified with stearic acid (N.S.: no sliding).
Syurface tension Surface contact Sliding angle
Liquid (mN/m) (20 C) angle (deg.) (SA) (deg.)
Wat er 7 2 0 158 2
Glycerol 636 156 3
Ethylene glycol 480 145 14
Olive oil 320 142 N.S.
solution at room temperature for 20 min and then heated
on a hot plate at 80 C for 1 hour to generate superhy-
drophobic surfaces. After coating with stearic acid, the
apparent contact angles of the untreated bare SS-400 and
Ag-doped ZnO nanorods fabricated on SS-400 substrates
were 111and 158, respectively. In addition to large CAs,
the Ag-doped ZnO nanorods fabricated on SS-400 sub-
strates also showed a low sliding angle (SA) of 2and
water droplets easily rolled off the substrate, as shown in
Figure 6. We also checked the performance of the fab-
ricated surface with several liquids of different surface
tensions, (Fig. 7 and Table I). The CAs for glycerol, ethy-
lene glycol, and olive oil were 156, 145, and 142,
respectively. Thus, we conclude that by altering the surface
energy of the textured surface with a low-surface-energy
material, superhydrophilic (or superamphiphilic) surfaces
can be easily transformed into superhydrophobic or oleo-
phobic (superamphiphobic) surfaces.
Finally, we applied our fabrication method to a helical-
type oil separator.27 A typical refrigerator consists of a
compressor, condenser, expansion valve, and evaporator.
In a refrigeration system, the compressor uses lubricating
oil along with the refrigerant which circulates in the sys-
tem. The compressor and condenser are the key parts of
Scheme 1. Schematic diagram of the experimental set-up.
a refrigeration system. The compressor needs lubricating
oil to improve its working efficiency and it is important to
separate the oil from the refrigerant for both the prevention
of failure and higher system efficiency. Thus, an oil sepa-
rator is installed between the compressor and condenser to
separate oil vapours from those of the refrigerant, which
helps to maintain the compressor oil level and raises the
efficiency of the system by preventing excessive oil cir-
culation (Schematic 1). We used SS-400 material because
it is cost-effective compared to other metals used to build
real oil separators. Oil separators generally consists of a
cylindrical container and a helical body part whose lengths
were 34 cm and 18.2 cm, respectively. The inner walls of
the cylindrical container and the helical part of the oil sep-
arator were treated with our fabrication method to create
superamphiphilic surfaces. Figure 8 shows the oil separa-
tor made of SS-400 material before and after applying our
method to fabricate Ag-doped ZnO nanorod surfaces. It is
clear that the uniform layer of Ag-doped ZnO nanorods
was fabricated on the inner walls of the oil separator; even
the helical part was covered uniformly with the fabricated
surface.
We compared the oil separation efficiency and pres-
sure drop between a commercial oil separator (Henry
Helical S-5182, USA) and our superamphiphilic oil sep-
arator equipped with the fabricated SS-400 surface. Oil
separation efficiency is defined as the ratio of separated
oil to the mixture of oil and refrigerant discharged from
the compressor. As compressed air passed through the oil
mist generator, it was sprayed with oil particles and passed
through the oil separator. The oil particles were trapped
in the container at the bottom of the fabricated superam-
phiphilic oil separator, and the air was released from the
oil separator. The ratio of the amount of collected oil to the
amount of sprayed oil was calculated and the separation
1600 Sci. Adv. Mater., 8, 1595–1602, 2016
Barthwal et al. Fabrication of a Superamphiphilic SS-400 Oil Separator Surface Using a Ag-Doped ZnO Nanorod Coating
ARTICLE
Fig. 8. Oil-separator made of SS-400 consisting of cylindrical and helical body parts, (a) before treatment, (b) after treatment with our fabrication
method; (c) a picture of the assembled helical-type oil separator.
Fig. 9. Comparison of oil separation efficiency and pressure drop between a commercial oil separator (Henry S-5182) and our superamphiphilic oil
separator equipped with the fabricated SS-400 surface.
efficiency was measured. This was expressed by the fol-
lowing equation:28
xef =
Qt
Qd
(1)
where xef denotes the separation efficiency, Qtis the
amount of oil trapped in the oil separator, and Qdis the
amount of sprayed oil.
Similarly, the pressure drop of the oil separator was
measured by differential pressure gauges installed in the
inlet and outlet of the oil separator. As shown in Figure 9,
the oil separator equipped with the superamphiphilic
SS-400 surface shows better oil separation efficiency by
up to 91.2% with a lower pressure drop compared with the
commercial version. Thus, we conclude that our simple
method can be implemented easily for fabricating super-
amphiphilic surfaces which can be applied to large-scale
processes and applications.
4. CONCLUSIONS
In summary, a cost-effective and time-saving method was
demonstrated to fabricate superamphiphilic surfaces on
SS-400 substrates. Ag-doped ZnO nanorods were synthe-
sized using a facile hydrothermal technique to create these
surfaces. The fabricated surfaces show excellent super-
amphiphilic properties with water and olive oil owing to
enhanced surface roughness and complete spreading of
liquids to near-zero contact angles. Furthermore, the fab-
ricated Ag-doped ZnO nanorod surfaces showed excel-
lent superamphiphilic properties that were stable under
long-term storage, thermal, and mechanical tests. We also
demonstrated that, after coating with a low-surface-energy
material, the fabricated superamphiphilic surfaces can eas-
ily be converted into superhydrophobic/oleophobic sur-
faces. Finally, we applied our fabrication method to a
helical-type oil separator made of SS-400 material to
demonstrate that the fabrication technique developed can
be useful in achieving superamphiphilic properties on
large-scale or 3D surfaces. Based on experimental results,
the oil separator treated with our fabrication method to
create superamphiphilic surfaces showed higher separa-
tion efficiency and lower pressure drop compared with
a commercial-type oil separator. Hence, we believe that
this simple, time-saving, and cost-effective method pro-
vides a new perspective for the industrial fabrication of
superamphiphilic surfaces suited to various environmental
conditions.
Sci. Adv. Mater., 8, 1595–1602, 2016 1601
Fabrication of a Superamphiphilic SS-400 Oil Separator Surface Using a Ag-Doped ZnO Nanorod Coating Barthwal et al.
ARTICLE
Acknowledgments: This work was supported by the
Global Excellent Technology Innovation (10038702,
Nature Inspired Smart Water/Solvent Collection Technol-
ogy) and the Human Resources Development of the Pro-
gram (No. 20134010200580) of the Korea Institute of
Energy Technology Evaluation and Planning (KETEP)
grant funded by the Ministry of Trade, Industry and Energy
(MOTIE) of Republic of Korea. It was also supported by
the Global Scholarship Program for Foreign Graduate Stu-
dents at Kookmin University, Republic of Korea.
References and Notes
1. Y. Kwon, N. Patanker, J. Choi, and J. Lee, Langmuir 25, 6129
(2009).
2. L. Liu, F. Xu, and L. Ma, J. Phys. Chem. C 116, 18722 (2012).
3. C. H. Xue, Y. R. Li, P. Zhang, J. Z. Ma, and S. T. Jia, ACS Appl.
Mater. Interfaces 6, 10153 (2014).
4. S.C.Cha,E.K.Her,T.J.Ko,S.J.Kim,H.Roh,K.R.Lee,K.H.
Oh, and M. W. Moon, J. Colloid Interface Sci. 391, 152 (2013).
5. N. J. Shirtcliffe, G. McHale, M. I. Newton, and C. C. Perry,
Langmuir 19, 5626 (2003).
6. Y.Liao,C.H.Loh,R.Wang,andA.G.Fane,ACS Appl. Mater.
Interfaces 6, 16035 (2014).
7. L. Zhai, C. F. Cebeci, R. E. Cohen, and M. F. Rubner, Nano Lett.
4, 1349 (2004).
8. S. H. Li, H. J. Li, X. B. Wang, Y. L. Song, Y. Q. Liu, L. Jiang, and
D. B. Zhu, J. Phys. Chem. B 106, 9274 (2002).
9. W. Xu, J. Song, J. Sun, Y. Lu, and Z. Yu, ACS Appl. Mater. Interfaces
3, 4404 (2011).
10. Yong, F. Chen, Q. Yang, D. Zhang, G. Du, J. Si, F. Yun, and X. Hou,
J. Phys. Ch em. C 117, 24907 (2013).
11. A. Fujishima, X. T. Zhang, and D. A. Tryk, Surf. Sci. Rep. 63, 515
(2008).
12. Z. H. Liu and Y. H. Qiu, ASME Journal of Heat Transfer 128, 726
(2006).
13. L.Zhai,M.C.Berg,F.A.Cebeci,Y.Kim,J.M.Milwid,M.F.
Rubner, and R. E. Cohen, Nano Lett. 6, 1213 (2006).
14. A. Lee, M. W. Moon, H. Lim, W. D. Kim, and H. Y. Kim, Langmuir
28, 10183 (2012).
15. T. Shimizu, T. Goda, N. Minoura, M. Takai, and K. Ishihara,
Biomaterials 31, 3274 (2010).
16. R. Wang, K. Hashimoto, A. Fujishima, M. Chikuni, E. Kojima,
A. Kitamura, M. Shimohigoshi, and T. Watanabe, Nature 388, 431
(1997).
17. D. Tahk, T.-I. Kim, H. Yoon, M. Choi, K. Shin, and K. Y. Suh,
Langmuir 26, 2240 (2010).
18. W. X. Huang, M. Lei, H. Huang, J. C. Chen, and H. Q. Chen, Surf.
Coat. Technol. 204, 3954 (2010).
19. J. Mao, Y. Chu, Y. J. Zhuo, and L. H. Dong, Colloids Surf. A 352, 18
(2009).
20. M. Eita, L. Wågberg, and M. Muhammed, J. P hys . Che m. C
116, 4621 (2012).
21. H. Guo, P. Sun, Y. Liang, Y. Ma, Z. Qin, and S. Cui, Chem.Eng.J
253, 198 (2014).
22. Y. Liu, B. Wang, E. Li, X. Song, H. Yan, and X. Zhang, Colloids
Surf. A 404, 52 (2012).
23. F. Shi, X. X. Chen, L. Y. Wang, J. Niu, J. H. Yu, Z. Q. Wang, and
X. Zhang, Chem. Mater. 17, 6177 (2005).
24. X. Liu and J. He, Langmuir 25, 11822 (2009).
25. Y. Masuda and K. Kato, Thin Solid Films 544, 567 (2013).
26. R. N. Wenzel, J. Phys. Ch em. 53, 1466 (1949).
27. S. Jang, J. Ahn, and S. H. Lim, Int. J. Precis. Eng. Manuf. 16, 2205
(2015).
28. B. H. Kang, K. J. Kim, and S. K. Lee, Int. J. Air-Cond. Refrig.
17, 88 (2009).
1602 Sci. Adv. Mater., 8, 1595–1602, 2016
... Pt, Au, Ag, and Pd) in gas-sensing materials. [25][26][27][28] However, the gas performance of the ZnO structure with Co content has seldom been explored. As a comparatively inexpensive noble metal, Co 2+ ion is a potential candidate that can be successfully doped and is compatible with Zn 2+ ion. ...
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In this investigation, gas sensors based on zinc oxide (ZnO) nanorods (NRs) with Co concentration were successfully fabricated and explored. A 100 nm-thick ZnO film was deposited as a seed layer onto Corning glass substrate via radio frequency (RF) magnetron sputtering technique. Then, Co-doped ZnO (CZO) NR arrays were grown by using a simple chemical bath deposition (CBD) method at 95 °C for 3 h and annealing at 450 °C, in which the Co-doping contents are 0, 5, and 10 mM. The surface-tovolume ratio of CZO NRs was higher than that of the pure ZnO structure. X-ray diffraction (XRD) results showed that the synthesised NRs were a single crystalline of the hexagonal wurtzite structure with uniform growth orientation of the c-axis. In addition, increasing ethanol (C2H5OH) response depends on O vacancy (VO) adsorption, which is measured via photoluminescence (PL) emission. Compared with pure ZnO NRs, the results showed that the CZO-5 (with 5 mM Co solution) NRs exhibited a superior sensitivity in C2H5OH gas applications and a fast response/recovery time. Meanwhile, the CZO-5 gas sensor presented a high response rate of 90.71% at 300 °C operating temperature when the concentration of ambient C2H5OH gas was 100 ppm.
... 하지만 실제 냉동 사이클에 연계한 실험에서 접촉각이 작은 표면의 경우 압력강하도 함께 증가하는 단점이 발견되었다. (12,13) 수치해석을 통해 입구 유동이 유분리기 내부 구조물과 충돌하면서 난류 운동 에너지가 생성되는 것을 확인하였고 (10,11) 이를 피하기 위한 설계로서 Fig. 1 (14) 이에 본 연구에서는 Fig. 1 표면 처리의 경우 선행 연구 (12) 에서 나선구조물과 몸체 모두 친유처리를 한 경우에 가장 분리효율이 높게 나타나 본 연구에서도 Fig. 3 ...
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The effects of oil wettability on the performance of a cyclone-type oil separator was studied through in situ experimentation and in a real refrigeration system. Based on previous research, the geometry of the oil separator in the present study was designed with an oil recovery device installed at its bottom to mount it on the actual refrigerator. The performance of the oil separator without surface treatment was predicted by applying design correlations proposed in the open literature, which were then compared with the experimental data. Through surface treatment, oleophilic or oleophobic properties were given to the inner wall and helix of the oil separator, and its performance was measured in a real refrigeration system. Oil wettability had a great effect on the performance of the oil separator, and in order to obtain high separation efficiency, oleophilic properties were found to be advantageous not only in the inner wall but also in the helix.
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SnO2 films were fabricated on fluorine-doped tin oxide (FTO) substrates in aqueous solutions. The films of about 800 nm in thickness grew in the solutions containing SnF2 of 25 mM at 90 °C for 24 h. They consisted of nanosheets of about 5-10 nm in thickness and about 100-1600 nm in plane size. The films had gradient structure of nanosheets. Smaller nanosheets formed dense structures in a bottom area, while larger nanosheets formed porous structures in a surface area of the films. The SnO2 films showed higher transparency than bare FTO substrates in a visible light region of 470 to 850 nm. Decrease of reflectance increased transparency. The SnO2 films had superhydrophilic surfaces of static contact angle below 1°. Nanosheet-assembled structures contributed high hydrophilicity. The surfaces were further modified with light irradiation. High speed camera observation showed that spread speed of water was improved with the irradiation. Removal of surface adsorbed organic molecules and increase in the number of hydroxyl groups brought superhydrophilicity and high spread speed.
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The ability to control the surface wettability of solid substrates is important in many situations. Here we report the photogeneration of a highly amphiphilic (both hydrophilic and oleophilic) titanium dioxide surface. The unique character of this surface is ascribed to the microstructured composition of hydrophilic and oleophilic phases, produced by ultraviolet irradiation. The result is a TiO2-coated glass which is antifogging and self-cleaning.
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This article describes a simple and convenient method to fabricate hierarchically structured coatings on glass substrates from soda lime glass by one-step hydrothermal method. The surfaces of the coatings are rough and are composed of flower-like particles assembled by nanoflakes or urchin-like particles constructed by nanowires. These rough surfaces exhibit superhydrophilicity, their water contact angles reaching 0 degrees in less than 40 ms. After surface modification by 1H,1H,2H,2H-perfluorooctyltriethoxysilane, the wetting properties of these coatings switch from superhydrophilicity to superhydrophobicity, with water contact angles as high as 160 degrees and slide angle as low as 1 degrees . The formation mechanism of the hierarchically structured coatings is discussed in detail on the basis of experimental results.
  • Y Kwon
  • N Patanker
  • J Choi
  • J Lee
Y. Kwon, N. Patanker, J. Choi, and J. Lee, Langmuir 25, 6129 (2009).
  • L Liu
  • F Xu
  • L Ma
L. Liu, F. Xu, and L. Ma, J. Phys. Chem. C 116, 18722 (2012).
  • C H Xue
  • Y R Li
  • P Zhang
  • J Z Ma
  • S T Jia
C. H. Xue, Y. R. Li, P. Zhang, J. Z. Ma, and S. T. Jia, ACS Appl. Mater. Interfaces 6, 10153 (2014).
  • S C Cha
  • E K Her
  • T J Ko
  • S J Kim
  • H Roh
  • K R Lee
  • K H Oh
  • M W Moon
S. C. Cha, E. K. Her, T. J. Ko, S. J. Kim, H. Roh, K. R. Lee, K. H. Oh, and M. W. Moon, J. Colloid Interface Sci. 391, 152 (2013).
  • N J Shirtcliffe
  • G Mchale
  • M I Newton
  • C C Perry
N. J. Shirtcliffe, G. McHale, M. I. Newton, and C. C. Perry, Langmuir 19, 5626 (2003).
  • Y Liao
  • C H Loh
  • R Wang
  • A G Fane
Y. Liao, C. H. Loh, R. Wang, and A. G. Fane, ACS Appl. Mater. Interfaces 6, 16035 (2014).
  • L Zhai
  • C F Cebeci
  • R E Cohen
  • M F Rubner
L. Zhai, C. F. Cebeci, R. E. Cohen, and M. F. Rubner, Nano Lett. 4, 1349 (2004).