一种快速制备超疏水表面的方法

A Rapid One-Step Fabrication of Patternable Superhydrophobic Surfaces Driven by Marangoni Instability

Sung-Min Kang, †Sora Hwang, †Si-Hyung Jin, †

Daeyeon Lee, §and Chang-Soo Lee *, †Chang-Hyung Choi, †Jongmin Kim, †Bum Jun Park, ‡

†Department of Chemical Engineering, Chungnam National University, Yuseong-gu, Daejeon 305-764, South Korea

‡Department of Chemical Engineering, Kyung Hee University, Yongin-si, Gyeonggi-do 446-701, South Korea

§Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States *Supporting Information

The fabrication of superhydrophobic surface is a fast growing roughening of the surface of hydrophobic materials, the area in both scienti fic and technological fields because of their chemical modi fication of the surface with fluorinated chemicals unique water-repellent and self-cleaning properties and their of low surface energy (bottom-upapproach), 4,13,14and physical potential for practical applications ranging from biotechnology formation of micro/nanostructurethrough silicon fabrication to self-cleaning commodity materials such as rain-or snow-techniques including etching, deposition, or photolithography proof glass, stain-resistant textiles, self-cleaning tra ffic signs, (top-downapproach). 15−18However, these approaches typi-micro fluidic devices, and functional separation equipment. 1−12cally involve multistep, time-consuming procedures, harsh Superhydrophobicity is explained by the Cassie −Baxter model preparation conditions, limited substrates, specialized chemical according to which air is trapped in the microgrooves of the modi fiers or reagents, and equipment. In addition, they are rough surface expensive and only applicable to small area or speci fic materials.

2,4,5and water droplets rest on the microstructured surface. Nature utilizes the extreme water-repellent proper-As a result, practical applications of such functional materials ties of have not been fully realized, and there is a clear need for an

−superhydrophobic 3surfaces in many plants and animals. 1Well-known examples include lotus leaves and inexpensive and broadly applicable approach toward super-water striders that are able to walk on the surface of water. hydrophobic coatings.

Based on the understanding of the relationship between Recently, alternative approaches have been developed to surface energy and roughness of natural nonwetting surfaces, a enable the straightforward fabrication of superhydrophobic

surfaces using the phase separation of polymers. 19−21The number of approaches inspired by nature open routes toward major route of the phase separation method is coating of a fabrication of arti ficial superhydrophobic surfaces; the speci fic polymer and then treating the coating with a nonsolvent for the

micro −nano binary structures dramatically increase the surface polymer at a speci fic temperature and under certain humidity roughness and minimize the contact area between the conditions. Thus, the relevant selection of solvents and the structures and the liquid. For water repellency, especially precise control of temperature or relative humidity may impose surface roughness and low surface energy are essential. A water limitation to scale-up for creating large-area uniform coatings or drop gently deposited on the surface shows a contact angle

above 150°and rolls o ffeasily, demonstrating the surface ’s Received:July 13, 2013

superhydrophobicity. Published:February 24, 2014

Figure Marangoni 1. Fabrication flow (case1) of and superhydrophobic generation of smooth surface. surface (A)Formation when glass of cover superhydrophobic is applied (casesurface 2). (B)containing Static contact micro-angle and of nanostructure water on the driven fabricated by polymeric heterogeneous surface with various cover materials.

process is almost evaporation. identical, the Evaporation surface would (solidbe arrows) (C)

preserved occurs Schematic

to its over inherent the diagram entire property interface of the fabrication

during between evaporation coating process,

and solution depicting Marangoni flow induced by

photopolymerization. and cover. If the rate However, of evaporation the rate of tension evaporation area to is higher heterogeneous interfacial beneath tension the area, PDMS is induced cover, inducing to replenish Marangoni coating flow. fluid, Thus, which a capillary ultimately flow leads (dottedto the arrows), formation from of the binary lower surface micro/nanostructures.

selective patterning of the superhydrophobic surfaces on straightforward patterning of superhydrophobic features is substrates. highly desirable.

Patterning superhydrophobic surface as another technical Here, we present an inexpensive and broadly applicable issue is especially important for numerous applications method that facilitates the preparation of patternable super-including hydrophobic surfaces with exceptional water repellency using

16,22,23water harvesting, bioassay, micro fluidics, and fluid transport. However, microscale patterning of super-Marangoni instability and photopolymerization. We demon-hydrophobic structures typically requires multiple steps and strate one-step formation of a superhydrophobic surface using a cannot be scaled up easily. Also, most of the previous methods trimethylpropane triacrylate (TMPTA)monomer solution in tend to focus on patterning hydrophilic regions on super-ethanol

hydrophobic surfaces, rather than directly patterning super-“as a coating solution on the substrate, following a hydrophobic structure on a hydrophilic surface. Directly coating spread, solution cover, and containing photopolymerization photoinitiator (SCP)is directly ”route. spread The patterning superhydrophobic features on glass, for example, onto a clean slide glass, followed by the placement of a PDMS would allow for subsequent functionalization of glass using the cover on top of the precursor solution and subsequently silane chemistry, which would provide versatility in controlling photopolymerization triggered by UV irradiation. A super-the surface wettability and properties for a variety of hydrophobic film is immediately obtained without any

additional treatment, where uneven evaporation and cluster applications. Thus, the development of methods to enable formation of the polymer take place to a fford

superhydrophobic

Figure 2. E ffect of ethanol concentration on the fabrication of superhydrophobic surface. SEM images at (A)10%,(B)20%,(C)30%,(D)40%,(E)50%,droplet (F)on 60%,each (G)surface. 70%,(H)(J)Static 80%,and water (I)contact 90%ethanol. angle on The each precursor film. (K)solution Analysis comprises of roughness TMPTA at and each ethanol. film. Scale The bars inset are image 300show nm.

a static water surfaces with the desired combination of micro-and nanoscale formation of porous polymer structures that have micro-and roughness. Consequently, the morphology of the binary nanoscale hierarchical structures. architecture in the superhydrophobic surface can be simply and e fficiently controlled by changing the concentration of To better understand the formation mechanisms of the ethanol and the use of PDMS cover. We also demonstrate that superhydrophobic morphology from the precursor solution, we these superhydrophobic surfaces can be readily patterned on examine the in fluence of solvent evaporation on the fabrication glass using a simple molding technique. We envision that these of superhydrophobic surfaces using di fferent types of covers. surfaces will be useful in fluid handling and transportation, The concentration of ethanol is kept constant at 50%.The optical sensing, medicine, and as self-cleaning and antifouling e ffect of di fferent covers on creating superhydrophobic surfaces materials is summarized in Figure 1B and Figure S1. We find that the ■operating in extreme. water contact angle increases when a PDMS or a PDMS/glass

RESULTS AND DISCUSSION cover is used, which demonstrates the use of the PDMS cover

has a signi ficant in fluence on the formation of super-

Our strategy based on a simple “spread, cover, and photo-hydrophobic surfaces. There is little di fference in water contact polymerization (SCP)”route to generate a superhydrophobic angles when the PDMS and PDMS/glasscovers are used. surface is schematically shown in Figure 1A. Interestingly, we However, in case of maximized retardation of solvent have found that a superhydrophobic surface showing rough evaporation with a glass cover and free evaporation without topology and exhibiting a water contact angle above 160°can the use of any covers, we cannot obtain a superhydrophobic be fabricated by placing a PDMS cover above the precursor surface.

solution during photopolymerization (case1). If a nonporous In the case of the PDMS or PDMS/glasscover, the result of glass cover is used during photopolymeziation, we are able to high contact angle value (above160°) implies that large obtain a hydrophilic surface rather than a superhydrophobic or volumes of air is trapped under a water droplet in the surfaces, hydrophobic one (case2). The topology of the hydrophilic resulting from high surface roughness. In other words, surface is smooth and flat. These results indicate that the key increasing the surface roughness of the film plays a major step in the generation of superhydrophobic surface is the role in rendering the surface superhydrophobic. The

photo-

polymerization under the limited evaporation condition (viasurfaces are fabricated with high water contact angles (>160°) the use of a PDMS or a PDMS/glasscover) results in di fferent (Figure2D −I). Owing to the extremely low adhesion of water surface wettabilities because the porous structure of PDMS to the coating, it is di fficult to deposit water drops on the likely plays a decisive role in fabricating superhydrophobic coatings with high contact angles. For instance, only PDMS and superhydrophobic surfaces; that is, water droplets immediately PDMS/glasscovers provide limited evaporation environment roll o ffupon their placement on these superhydrophobic during the photopolymerization. Thus, this phenomenon surfaces, which indicates that our fabrication method induces indicates that the limited evaporation of solvent in photo-superhydrophobic properties in a simple and rapid manner. polymerization can play a vital role in the generation of Phase-shifting interferometry images of surface morphologies superhydrophobic surfaces (>160°) with di fferent surface of the surface and their corresponding roughness also highlight morphology. the in fluence of the concentration of ethanol on both the We believe that the results can be explained by Marangoni surface hydrophobicity and the surface morphology (FigureS2instability induced by the limited evaporation of the solvent and Figure 2J). As we expected, roughness analysis shows that during photopolymerization. Figure 1C outlines the proposed the surface roughness increases from low to high concen-mechanism for the formation of binary micro/nanostructurestrations of ethanol. While the surfaces obtained at low via the Marangoni flow, driven by the combined solvent concentration of ethanol (below30%)are not structured, evaporation and photopolymerization. First, a film of the high concentration of ethanol leads to the formation of micro-coating solution is spread on the substrate and covered with a and/ornanostructure. When the concentration of ethanol is PDMS slab. Subsequently, the precursor solution under PDMS above 40%,coral-like surface morphologies are generated with is exposed to UV irradiation triggering photopolymerization. As large numbers of micrometer-scale spherulites decorated with volatile ethanol unevenly evaporates through the highly nanometer-sized fine structures, achieving high roughnesses permeable PDMS cover during photopolymerization, the (above1.4μm). In other words, an increase in the evaporation of the solvents induces cooling near the surface concentration of ethanol results in an increase in the formation and leads to the formation of temperature gradient between the of binary structure with micro-and nanosized spherical top layer (Taggregates. It is interesting to see that the polymerized films

1) and bottom surface (Ttemperature are simultaneously 2). Finally, the gradients in composition and induced in the without signi ficant surface roughnesses are hydrophilic. We thin precursor solution, as shown in Figure 1C because believe the polymerized film under limited evaporation interfacial tension is a function of solution temperature and provides re-entrant microstructures that renders these surfaces concentration. The gradients change the interfacial tension, superhydrophobic. 27

inducing flow near the surface of the precursor film. The high In addition, we have investigated the bouncing of a droplet as interfacial tension area pulls the solution from the low dynamic e ffect of superhydrophobic surface because the ability interfacial tension area; a surface tension gradient (dottedof water to bounce on a surface provides an indication of the arrow in Figure 1C scheme) and hence a Marangoni flow surface properties (FigureS3). The result also con firms the develop and drive the aggregation of polymers toward the high hydrophobicity of a surface, with a relationship established interfacial tension area to form micro/nanostructures.24−26between water contact angle and number of bounces, which is Therefore, in this case, the Marangoni flow is mainly attributed dependent on the surface microstructure. 28,29

to the di fference in the interfacial tension, which is responsible In short, the increase in the concentration of ethanol under for the formation of binary micro/nanostructures.This the photopolymerization of the monomer has two major hypothesis is also supported by the use of di fferent covers consequences:(1)inhomogeneous or limited evaporation of (Figure1B). the volatile solvent, ethanol, through a porous PDMS cover The quanti fication of the changes in the water contact angle provides the Maragoni instability in the precursor solution; (2)and the evaporation results in the localization of monomers, which fisurface roughness form nuclei for the formation of micro/nanoclustersand, as a hydrophobic rst step toward under di fferent conditions provides a surface understanding formation. First, the to principle investigate of the super-role consequence, binary structures are formed. The resulting of the ethanol in the formation of superhydrophobic surfaces, surface morphology and roughness have a signi ficant e ffect we determine water contact angle and roughness as a function on the water-repellent properties. Our method provides a of ethanol concentration, averaged over five experimental straightforward and simple method to generate superhydro-results (Figure2). The fabrication of the thin film with di fferent phobic surface.

concentration of ethanol is performed, and the surface The superhydrophobic surfaces prepared using our SCP properties of the prepared films are examined with a scanning method can be used for diverse applications owing to its electron microscope (SEM),water contact angle measure-excellent water repellency. We present three examples of ments, and phase-shift interferometry. applications using our superhydrophobic surface in self-The surface morphology and water contact angle of the cleaning, selective oil removal, and one-step patterning. Lotus polymerized surfaces depend signi ficantly on the concentration leafs, natural superhydrophobic surfaces, are well-known of ethanol in the precursor solution. When the concentration of examples of self-cleaning surfaces. 1,3,6When a water droplet ethanol is below 20%,little surface features are observed. The is placed on a particle-contaminated superhydrophobic surface, surface formed with low concentration of ethanol solvent (10the droplet captures the particles on the surface while it is and 20%w/v)shows small increase of hydrophobicity with a moving around on the surface. The adsorption of the particles water contact angle of 74°and 83°, respectively (Figure2A,B). is due

The polymerized surface at 30%ethanol is structured; however, 30to the strong attachment of particles to the droplet surface. We con firm the e ffectiveness of the superhydropho-the surface roughness is not su fficient to induce super-bic surface in self-cleaning toward particle contamination. hydrophobic properties (Figure2C). When the concentration When the surfaces contaminated with co ffee, cream, and sugar of ethanol is raised above 40%ethanol, superhydrophobic powders are rinsed with water, the liquid forms into droplets

and collect dirt from the surface while it freely moves around As a last example, we demonstrate one-step complex pattern on the surface (Figure3A). formation of superhydrophobic surfaces using micromolding in capillaries (MIMIC)(Figure4and Figure S5). 34,35By slightly

Figure patterning 4. using Schematic micromolding diagram in for capillary selective (MIMIC):superhydrophobic (A)PDMS micromold solution placement, (B,

Figure radiation, by (E)capillary C) filling the micromold with a precursor

removing action, the (D)PDMS the curing micromold. of prepolymer (F)Selective by UV

cleaning, 3. patterning

phase

system. oil Diverse capture applications in (B)oil of and superhydrophobic water, and (C)water surface:and (A)oil two-self-

stration of of infosurface superhydrophobic using selective surface patterning onto substrate. of superhydrophobic (G)Demon-

surface. Scale bar:300μm.

We examine the capability of the superhydrophobic surface modifying the SCP method, we can achieve a single-step to selectively capture oil and transport the fluid. Such a material patterning of superhydrophobic surfaces directly on glass. First, is especially important because the number of environmental we prepare a lithography mask that contains information in the accidents involving oil spills has been on the rise in the recent form of a barcode or a Quick Response (QR)code, which is years; for example, the Deep Horizon oil spill in the Gulf of then used to fabricate a PDMS micromold. The micromold, Mexico seriously damaged the ocean in 2010. Functional which can be used repeatedly, is placed on a glass surface, and materials that 33can remedy these situations are in high the precursor solution is introduced to one side of the demand. 31−We demonstrate the selective oil capture process micromold by capillary action (Figure4A −F). Through in two-phase systems. For example, we have made a two-phase capillarity, the solution is wicked into the patterned region solution composed of olive oil (dyedwith a red dye) and water between the mold and the glass surface. The precursor is (dyedwith a blue dye). Because the density of olive oil is lower polymerized under UV irradiation to form a patterned than that of water, olive oil forms the superphase, whereas superhydrophobic surface (Figure4F). water forms the subphase. Figure 3B illustrates selective oil Remarkably and unexpectedly, these superhydrophobic absorption by simply immersing the superhydrophobic surface patterns exhibit strong fluorescence although no fluorescent into the water phase through the oil phase. Interestingly, the molecules color of the polymer surface turns red, indicating that the polymer surface selectively absorbs the oil. Conversely, we have flcorrelates uorescence have strongly observed been added with over to the roughness a the wide structure. of range The the surface of intensity wavelength of (Figuremade a di fferent two-phase system composed of transparent S5), which can be tuned by the concentration of ethanol in the FC-40as the oil phase and water containing a red food dye. In precursor solution prior to photopolymerization. In short, the this case, the oil phase is the subphase because its density is rougher the surface is the stronger the fluorescence intensity. higher than that of water. Although the superhydrophobic Also, the fluorescence from these patterns is very stable and can surface comes in contact with water first during its immersion, be observed for 6months after sample preparation with little the surface does not show any red color and only absorb protection transparent FC-40oil while retaining its original opaque appearance (Figure3C). In addition, we have performed a flfrom ambient light photopolymerized uorescence may be polymer; attributed however, to and auto oxygen. The strong we fluorescence do not of clearly the removal test of n -decane using this surface as a sponge. When a understand its physical mechanism and origin. The stable and droplet of decane is placed on the surface, the decane drop is strong fluorescence in this patternable superhydrophobic rapidly absorbed into the surface (FigureS4A) and transports surface, nevertheless, presents a new opportunity to generate across the surface (FigureS4B). what we call “infosurface ”that contains information in the

form

of (6)Liu, K. S.; Yao, X.; Jiang, L. Recent developments in bio-inspired flspecial useful uorescence superhydrophobic microscopy. patterns These that structures can be readily can detected be using ■in applications that require protection against especially moisture. (7)Verho, wettability. T.; Bower, Chem. C.; Soc. Andrew, Rev. 2010P.; Franssila, , 39, 3240S.; −3255. Ikkala, O.; Ras, R.

H. A. Mechanically durable superhydrophobic surfaces. Adv. Mater.

CONCLUSIONS 2011To enable commercialization of superhydrophobic coatings, a (8), Anastasiadis, 23, 673−678. S. H. Development of functional polymer surfaces simple and e fficient fabrication process using accessible and with cost-e ffective materials and simple preparation conditions are (9)controlled Celia, E.; wettability. Darmanin, Langmuir T.; de Givenchy, 2013, 29, 9277E. T.; −9290. Amigoni, S.;

Guittard, F. Recent advances in designing superhydrophobic surfaces.

highly desirable. This study demonstrates a facile, simple, and J. fast fabrication route to obtain readily patternable super-(10)Colloid Dash, Interface S.; Garimella, Sci. 2013, S. 402V. , Droplet 1−18. evaporation dynamics on a hydrophobicity by using Marangoni instability. The super-superhydrophobic surface with negligible hysteresis. Langmuir 2013, hydrophobic 29, 10785−10795. “surfaces could be created through a simple (11)Lai, Y. K.; Pan, F.; Xu, C.; Fuchs, H.; Chi, L. F. In situ surface-without spread, need cover, for and the photopolymerize use of any fluorinated (SCP)materials ”procedure, and modification-induced superhydrophobic patterns with reversible sophisticated instruments. The technique described here can be wettability employed to mimic the special micro −nano binary structure of (12)Tuberquia, and adhesion. J. C.; Adv. Jennings, Mater. 2013G. K. , 25Surface , 1682−initiation 1686. from the lotus leaf under ambient conditions, especially suitable for adsorbed polymer clusters:A rapid route to superhydrophobic creating surfaces with complex shapes and patterns, such as QR coatings. and barcodes. We have also demonstrated the successful (13)Wu, ACS W. Appl. L.; Zhu, Mater. Q. Z.; Interfaces Qing, F. 2013L.; Han, , 5, 2593C. C. −2598. Water repellency application of the superhydrophobic surfaces in selective oil on a fluorine-containing polyurethane surface:Toward understanding capture and transportation. Our approach opens a truly simple, the surface self-cleaning effect. Langmuir 2009, 25, 17−20. (14)Wolfs, M.; Darmanin, T.; Guittard, F. Versatile super-rapid, and e fficient route to the generation of superhydrophobic hydrophobic surfaces from a bioinspired approach. Macromolecules surfaces, which may be extended to a wide variety of polymers. 2011Also, it contributes to the realization of superhydrophobic (15), Zhao, 44, 9286H.; −Law, 9294. K. Y.; Sambhy, V. Fabrication, surface properties, surfaces with an eco-friendly approach and opens new and origin of superoleophobicity for a model textured surface. perspectives ■on the application of Marangoni instability. Langmuir (16)Zhai, 2011L.; , 27Berg, , 5927M. −C.; 5935. Cebeci, F. C.; Kim, Y.; Milwid, J. M.;

ASSOCIATED CONTENT Rubner, M. F.; Cohen, R. E. Patterned superhydrophobic surfaces:*Toward a synthetic mimic of the Namib Desert beetle. Nano Lett. Supporting Information 2006Detailed experimental procedure and additional experimental (17), 6Kietzig, , 1213−1217. A. M.; Hatzikiriakos, S. G.; Englezos, P. Patterned results. This material is available free of charge via the Internet superhydrophobic metallic surfaces. Langmuir 2009, 25, 4821−4827. ■at http://pubs.acs.org.(18)Deng, X.; Mammen, L.; Butt, H. J.; Vollmer, D. Candle soot as a

template for a transparent robust superamphiphobic coating. Science

AUTHOR INFORMATION 2012Corresponding Author (19), Zhang, 335, 67Y.; −70. Wang, H.; Yan, B.; Zhang, Y. W.; Yin, P.; Shen, G. L.; *E-mail [email protected](C.-S.L.).Yu, R. Q. A rapid and efficient strategy for creating super-hydrophobic

coatings on various material substrates. J. Mater. Chem. 2008, 18,

Author Contributions 4442−4449. S.-M.K. and S.H. contributed equally to this work. (20)Zhao, N.; Xie, Q. D.; Weng, L. H.; Wang, S. Q.; Zhang, X. Y.; Notes Xu, J. Superhydrophobic surface from vapor-induced phase separation

of

■The authors declare no competing financial interest. (21)copolymer Erbil, H. micellar Y.; Demirel, solution. A. L.; Macromolecules Avci, Y.; Mert, 2005O. Transformation , 38, 8996−8999. of

a simple plastic into a superhydrophobic surface. Science 2003, 299,

ACKNOWLEDGMENTS 1377This study was supported by a grant from the National (22)−1380. Han, S.; Bae, H. J.; Kim, J.; Shin, S.; Choi, S. E.; Lee, S. H.; Research Foundation of Korea (NRF)funded by the Korean Kwon, S.; Park, W. Lithographically encoded polymer microtaggant government (MEST)(No.2011-0017322). D.L. acknowledges using high-capacity and error-correctable QR code for anti-counter-

feiting

■the support from the NSF (CAREERDMR-1055594). (23)Pretsch, of drugs. T.; Adv. Ecker, Mater. M.; 2012Schildhauer, , 24, 5924M.; −5929. Maskos, M. Switchable

REFERENCES information carriers based on shape memory polymer. J. Mater. Chem.

2012(24), 22Erbil, , 7757H. −7766. Y. Evaporation of pure liquid sessile and spherical

special (1)Sun, T. L.; Feng, L.; Gao, X. F.; Jiang, L. Bioinspired surfaces with suspended drops:A review. Adv. Colloid Interface Sci. 2012, 170, 67−

(2)Li, wettability. X. M.; Reinhoudt, Acc. Chem. D.; Crego-Calama, Res. 2005, 38, 644M. −What 652. do we need for 86. a (25)Cai, Y. J.; Newby, B. M. Z. Porous polymer films templated by preparation superhydrophobic of superhydrophobic surface? A review surfaces. on the Chem. recent Soc. progress Rev. 2007in , the 36, Marangoni flow-induced water droplet arrays. Langmuir 2009, 25, 13507638(26)−7645. Lu, S. Y.; Chen, H. L.; Wu, K. H.; Chen, Y. Y. Formation of antireflection (3)−Min, 1368. W. coatings. L.; Jiang, Adv. Mater. B.; Jiang, 2008P. , 20Bioinspired , 3914−3918. self-cleaning nanowire striations driven by marangoni instability in spin-cast

polymer

structures (4)Bhushan, (27)Tuteja, thin films. A.; Choi, Langmuir W.; Ma, 2007M. , 23L.; , Mabry, 10069−J. 10073. M.; Mazzella, S. A.; Philos. Trans. for B.;

R. superhydrophobicity, Jung, Y. C.; Koch, K.

Soc., A 2009, 367, 1631self-cleaning Micro-, nano-

−1672. and and low hierarchical adhesion. Rutledge, G. C.; McKinley, G. H.; Cohen, R. E. Designing

superoleophobic surfaces. Science 2007, 318, 1618−1622.

emerging (5)Nosonovsky, applications:M.; Non-adhesion, Bhushan, B. Superhydrophobic energy, green engineering. surfaces Curr. and (28)Richard, D.; Quere, D. Bouncing water drops. Europhys. Lett. Opin. Colloid Interface Sci. 2009, 14, 270−280. 2000, 50, 769−775.

(29)Lee, D. J.; Kim, H. M.; Song, Y. S.; Youn, J. R. Water droplet bouncing nanostructures. and superhydrophobicity ACS Nano 2012, 6, induced 7656−7664. by multiscale hierarchical Curr. (30)Binks, B. P. Particles as surfactants -similarities and differences.

(31)Opin. Hayase, Colloid G.; Kanamori, Interface Sci. K.; 2002Fukuchi, , 7, 21M.; −41. Kaji, H.; Nakanishi, K. Facile harsh conditions synthesis of for marshmallow-like the separation of macroporous oil and water. gels Angew. usable Chem., under Int. Ed. 2013, 52

durable (32)Wang, ,

superhydrophobic C. 1986F.; −Tzeng, 1989. F. zinc S.; Chen, oxide-coated H. G.; Chang, mesh films C. J. Ultraviolet-for surface and 10015underwater-oil capture and transportation.

(33)−Langmuir 2012, 28,

Xue, 10019. Z. X.; Wang, S. T.; Lin, L.; Chen, L.; Liu, M. J.; Feng, L.; Jiang, hydrogel-coated L. A novel mesh superhydrophilic for oil/waterand separation. underwater Adv. Mater. superoleophobic 2011, 23, 4270

Choi, (34)−Shim, 4273.

J. S.; H. Han, W.; J.; Lee, Lee, J. H.; C. S. Hwang, Patterning T. S.; of Rhee, proteins Y. W.; and Bae, cells Y. M.; on functionalized micromolding in surfaces capillaries. prepared Biosens. by Bioelectron. polyelectrolyte 2007, multilayers 22, 3188−3195. and capillaries:(35)Kim, E.; Xia, Y. N.; Whitesides, G. M. Micromolding in 118, 5722−Applications 5731.

in materials science. J. Am. Chem. Soc. 1996,