Regulating Underwater Oil Adhesion on Superoleophobic Copper

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Regulating Underwater Oil Adhesion on Superoleophobic Copper Films through Assembling n‑Alkanoic Acids Zhongjun Cheng,‡ Hongwei Liu,‡ Hua Lai,‡ Ying Du,‡ Kewei Fu,‡ Chong Li,‡ Jianxin Yu,§ Naiqing Zhang,*,†,‡ and Kening Sun*,†,‡ †

State Key Laboratory of Urban Water Resource and Environment, School of Municipal and Environmental Engineering, ‡Natural Science Research Center, Academy of Fundamental and Interdisciplinary Sciences, and §Center for Analysis and Measurement, School of Material Science and Engineering, Harbin Institute of Technology, Harbin, Heilongjiang 150090, P. R. China

Downloaded by GEORGETOWN UNIV on September 2, 2015 | http://pubs.acs.org Publication Date (Web): September 1, 2015 | doi: 10.1021/acsami.5b06374

S Supporting Information *

ABSTRACT: Controlling liquid adhesion on special wetting surface is significant in many practical applications. In this paper, an easy selfassembled monolayer technique was advanced to modify nanostructured copper substrates, and tunable adhesive underwater superoleophobic surfaces were prepared. The surface adhesion can be regulated by simply varying the chain length of the n-alkanoic acids, and the tunable adhesive properties can be ascribed to the combined action of surfaces nanostructures and related variation in surface chemistry. Meanwhile, the tunable ability is universal, and the oil-adhesion controllability is suitable to various oils including silicon oil, n-hexane, and chloroform. Finally, on the basis of the special tunable adhesive properties, some applications of our surfaces including droplet storage, transfer, mixing, and so on are also discussed. The paper offers a novel and simple method to prepare underwater superoleophobic surfaces with regulated adhesion, which can potentially be applied in numerous fields, for instance, biodetection, microreactors, and microfluidic devices. KEYWORDS: underwater superoleophobic, tunable adhesion, self-assemble, copper film, n-alkanoic acids

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INTRODUCTION Inspired by special oil-repellent ability of fish scales in water,1,2 underwater superoleophobic surfaces with oil contact angles higher than 150° have become a new research focus during the past decade,3−20 and the special oil-repellent ability allows them wide applications including self-cleaning of marine equipment,21 antibioadhesive,22,23 oil/water separation,24,25 small oil droplet transportation,26,27 and lab-on-chip devices.28 In these applications, control oil adhesion is significant since the surface adhesion can directly affect their practical applications. To satisfy various applications, surfaces that have tunable underwater oil adhesions are favorable, and it is significant to put forward new methods and novel materials for preparation of such surfaces. In the past few years, much progress has been made in developing such underwater superoleophobic surfaces with tunable adhesive properties, and this research found that the surface adhesive property is governed together by its chemical composition and microstructures.29−38 For example, through a free radical polymerization process, Chen et al. prepared a thermal-responsive PNIPAM hydrogel,29 on which the adhesive forces to oil droplet can be regulated by altering the temperature. By using the emulsion polymerization method, Huang et al. prepared a series of latex particles with different morphologies and reported controlled underwater oil adhesion on the films assembled with these particles.30 Some other examples include pH-trigged poly(acrylic acid) (PAA) surface prepared by the plasma polymerization process 31 and © XXXX American Chemical Society

construction of potential-modulated polyaniline nanowires/ polypyrrole film through the electrochemical polymerization process.36 Noticeably, almost all of these works are focused on preparing the polymer coatings, and the used methods have some limitations, for example, expensive materials, poor durability, tedious fabrication process, and severe fabrication conditions. In this regard, a novel and simple method for preparation of such tunable adhesive underwater superoleophobic surfaces would be necessary and highly desired. In this paper, by using the self-assembled monolayer technique,39,40 a series of underwater superoleophobic copper surfaces with controlled adhesion were prepared. Through modifying n-alkanoic acids with different chain lengths on the nanostructured copper films, surfaces with different oil adhesive forces can be obtained, less than 1 μN (modified by those molecules with carbon number less than 6), about 7−8 μN (modified by those molecules with carbon number 6 or 7), and larger than 58 μN (modified by those molecules with carbon number larger than 7), demonstrating highly controllability on our surfaces. Meanwhile, the special tunable adhesive ability allows us to demonstrate some applications such as droplets storage, transfer, mixing, and splitting with our surfaces. The surfaces reported here have such special controllable oil adhesive properties, and we believe they can potentially be Received: July 15, 2015 Accepted: August 26, 2015

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DOI: 10.1021/acsami.5b06374 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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ACS Applied Materials & Interfaces applied in many fields, for instance, microfluidic device, biodetection, and other adhesion-related applications.


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EXPERIMENTAL SECTION

Fabrication of Copper Film. The copper films were prepared through a simple sputtering process. Briefly, glass substrates were first cleaned with acetone and ethanol and finally dried with N2. Then these glass substrates were coated with copper films using a sputter-coater (Leica EM, SCD 500). The working distance between the glass substrates and the copper target is kept at 10 cm, the intensity of working current is 60 mA, and the sputtering time is about 600 s. After that, a layer of copper film with thickness of about 210 nm would be present on the glass substrates. Assembly of n-Alkanoic Acids on the Copper Films. After production of the copper films, the substrates were further immersed into the ethanol solution containing different n-alkanoic acids (0.001 M) for about 12 h.40 At last, the surfaces were cleaned by ethanol and dried under N2. Instrumentation and Characterization. The surface morphologies were measured on an atomic force microscope (AFM, Bruker, Dimension Icon) and a field emission scanning electron microscope (FESEM, HITACHI, SU8000). Surface chemical compositions were confirmed by X-ray photoelectron spectroscopy (XPS), obtained using Al Ka (1486.6 eV) radiation (Thermo Fisher Scientific Company). The surface wetting properties were carried on a contact angle meter (Shanghai Zhongchen, JC 2000D5). Droplets were dropped onto the surfaces directly for investigation in air. For investigation in water, the surfaces were first placed in a transparent cistern filled with water. The oil droplets were placed upon/beneath the surfaces according to the densities of the oils. The final values were calculated via averaging six different positions. The rolling angles were examined with a 4 μL oil droplet on the same contact angle meter. A high-sensitivity microelectromechanical balance system (Dataphysics DCAT 11, Germany) was used to examine the oil-adhesive forces. A metal ring that can capture the oil droplet (5 μL) was first installed to the above system. A stage with the surface underwater was raised at a rate of 0.01 mm s−1, and when the surface contacted the droplet, the stage began to leave. The forces were recorded during the whole process, and 1, 2dichloroethane was used as the test liquid. The photos shown in Figure 7, panel a were recorded by using a camera (Canon 70D).

Figure 1. SEM images viewed from (a) top and (b) side of the copper film on glass substrate after 600 s of sputtering, respectively; (c) 2D and (d) 3D AFM images of the copper film, respectively.

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RESULTS AND DISCUSSION In this paper, the copper films were produced on the glass substrates through a simple sputtering process (Figures S1 and S2). Figure 1, panel a displays the SEM image of the asprepared film. It can be found that the glass substrate has been covered fully by the copper particles. Some islands with the size of about 50− 250 nm were formed due to the accumulation of the copper particles, which can be observed clearly between the cracks on the surface. The cross-sectional image indicates that the thickness of the whole copper film is about 210 nm (Figure 1b). In addition to the SEM, the surface morphology was further investigated with AFM, one of the most powerful tools for surface nanostructures investigation. As is shown in Figure 1, panels c and d, the size of the copper nanogranules is in the range of 10−30 nm, and the surface roughness is about 4.77 nm from the analysis of the AFM results. After production of copper film, the substrates were immersed into the ethanol solution of n-alkanoic acids. The n-alkanoic acids molecules would adsorb onto the copper surfaces,45 which can be confirmed by the results of XPS. From Figure 2, panel a, it can be found that on the substrate modified by n-octanoic acid, elements Cu, C, and O can be seen clearly. On the high-resolution C 1s spectra, more detailed information can be found (Figure 2b). Compared with the original copper

Figure 2. (a) XPS survey spectrum of the sample modified by noctanoic acid; (b) high-resolution C 1s XPS spectra of the copper surface and that after modification by n-octanoic acid, respectively.

surface, the C 1s peak assigned to C−C/C−H at 284.8 eV is greatly enhanced (a weak peak on the original copper film can be found in the C 1s spectrum is ascribed to the impurity). Meanwhile, a peak at 288.2 eV ascribed to −COO arises, indicating that the n-octanoic acid molecules have been assembled onto the copper film successfully (Figure S3).41 B


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ACS Applied Materials & Interfaces

is further increased (with carbon number larger than 7), the obtained surfaces would be highly adhesive, and an oil droplet would be pinned tightly (herein, the sliding angle 90° means the droplet is in the pinning state). In addition to 1, 2dichloroethane, the surface underwater oil wettability was also tested by other oils including n-hexane, silicon oil, and chloroform. For these oils, superoleophobicity (Figure 4a)


From the above results, it is reasonable to conclude that the method used here is effective for assembling the n-alkanoic acids on the copper surface. By using a contact angle measure meter, the surface wettability was examined accurately. Figure S4 shows the results of water and oil (1, 2-dichloroethane) contact angles measured in air. It can be observed that all the obtained surfaces are superoleophilic, and the oil contact angles are less than 10°. Noticeably, for water, a remarkable variation of the contact angles can be observed, which is increased apparently with increasing the molecular chain length. The results are similar to Prof. Wang’s report, and such increase of water contact angles can further confirm that the n-alkanoic acids have been assembled on the copper films.40 In this work, underwater oil wetting performance and especially the surface adhesion are our major interests. Figure 3, panel a displays the oil contact angles on the surfaces before

Figure 4. Statistics of underwater oil (a) contact and (b) sliding angles for various oils on the surfaces modified with different n-alkanoic acids, respectively.

and controlled oil adhesion can also be observed on these surfaces (Figure 4b), indicating that the tunability of the surface adhesion is universal regardless of oil type. From the above results, it can be found that by simply controlling the chain length of n-alkanoic acids, surfaces with different adhesive properties for oil droplets in water can be prepared. Meanwhile, such controllability can be kept at least 1 week after the surfaces were placed in water or in air without special protection, indicating that the obtained surfaces have a good stability. The surface adhesive properties were further examined by a high-sensitivity microelectromechanical balance system through the approach, contact, and leave process, and the results are displayed in Figure 5. For surface modified by n-alkanoic acids with short chain length, such as n-propanoic acid, the adhesive force is less than 1 μN and difficult to be detected (Figure 5a). No apparent variation of the oil droplet during the investigation process can be observed (inset in Figure 5a). As the chain length is increased, for example, n-hexanoic acid (Figure 5b), the obtained surface adhesive force is increased to about 7.6 μN, and some distortion of the oil droplet can be observed

Figure 3. Underwater oil (a) contact angles and (b) sliding angles as a function of chain length of the used n-alkanoic acids, respectively. Surface modified by n-alkanoic acid with carbon number 0 represents the as-prepared copper film.

and after modification with different n-alkanoic acids in water. It can be found that for surfaces modified with different n-alkanoic acids, the contact angles are higher than 150°, meaning that superoleophilic surfaces in air become sueproleophobic in water. More interestingly, the dynamic actions of oil droplets on the surfaces can be regulated by varying the chain length of the n-alkanoic acids (Figure 3b). For surface modified by nalkanoic acids with short chain length (with carbon number less than 6), the surface is low adhesive. The sliding angle for a 1, 2dichloroethane droplet (4 μL) is less than 5°. With increasing the chain length (with carbon number of 6 and 7), the sliding angle would be slightly increased. As the molecular chain length C


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Figure 5. Force curves for surfaces modified with different n-alkanoic acids contact with the oil droplet: (a) n-propanoic acid; (b) n-hexanoic acid; (c) n-octanoic acid, respectively. (d) Statistic of the adhesive forces for different surfaces. Insets are the shapes of oil droplets at various stages during the measuring process.

would be very small (Figure 6b) because the molecular chains are disordered and scattered (Figure 6c). Meanwhile, because of the same reason, a lot of high-energy metal surface are exposed, and the surface shows hydrophilicity (Figure S4). When such hydrophilic surface is placed into water, the interspaces between the copper particles would be occupied by water, and the oil droplet would stand on a heterogeneous interface composed of water and solid (Figure 6a). The contact area fraction between solid and the oil droplet can be calculated according to the following modified Cassie equation:43,44

during the examining process (inset in Figure 5b). Further increasing the chain length would result in high adhesion on the surface. As shown in Figure 5, panel c, on surface modified with n-octanoic acid, the adhesive force (larger than 58 μN) is high enough to result in a large distortion of the droplet. After examination, some oil even was left on the surface (inset in Figure 5c). From the above results, it can be concluded that the surface adhesions can be regulated by varying the chain length of the modified n-alkanoic acids, and the surfaces with different oil adhesive forces can be obtained, less than 1 μN (modified by those molecules with carbon number less than 6), about 7−8 μN (modified by those molecules with carbon number of 6 or 7), and larger than 58 μN (modified by those molecules with carbon number larger than 7), indicating that good controllability can be observed on our surfaces (Figure 5d). The obtained surfaces have such special tunable adhesive abilities that can be interpreted by the following two points: the first is different amount of oleophilic alkyl groups on the surface for different n-alkanoic acids molecules, which can directly result in different oil-adhesive forces; the second is different oil/ solid contact areas due to different capillary effects that originate from the combined action of oleophilic alkyl groups and surface nanostructures. Figure 6, panel a depicts the underwater oil wetting state on the as-prepared surfaces. According to Tao’s report,42 the chain length of the n-alkanoic acid can influence the structure of self-assembled monolayer prominently. On the surface modified by n-alkanoic acids with short chain length, the number of oleophilic alkyl groups is scarce and the oil-adhesive force provided by the alkyl groups

′ = f cos θow + f − 1 cos θow

(1)

Herein, f represents the solid/oil area fraction, θ′ow represents underwater oil contact angle on the rough film, and θow represents the underwater oil contact angle on a smooth film. Taking the film modified by n-propanoic acid as an example, θ′ow = 162° (Figure 3), θow = 102° (Figure S5), and f = 0.062. It can be found that under the oil droplet, most of the contact area (larger than 93%) is the oil/water interface, and oil/solid interface is very small. Therefore, as shown in Figure 3, the oil droplets on surfaces modified by n-alkanoic acids with short chain length have high contact angles/extreme low sliding angles, and low adhesive forces to the oil droplet (Figure 5d). As the chain length is increased, the oil-adhesive force is increased since more oleophilic alkyl groups are present on the surface (Figure 6d). The increase of the oleophilic alkyl groups can be ascribed to that the packing of molecular chains becomes denser and more ordered with the increasing of chain length42 (Figure 6e). At the same time, the nanostructures are D


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oil droplet is placed onto the surface (Figure 6a). The solid/oil contact area fraction can also be calculated according to eq 1, which is 0.099 (obviously larger than the solid/oil area fraction 0.062 on n-propanoic acid modified surface; although the solid/ oil contact area is increased on surfaces modified by n-alkanoic acids with long chain length, the oil/water contact area is still the main fraction under oil droplet, and the surfaces can still show superoleophobicity), indicating that as the chain length is increased, the solid/oil contact area is also increased. Therefore, as shown in Figure 3, panel b and Figure 5, panel d, the surfaces modified with long chain length molecules have high adhesive forces, and the oil droplet is pinned on these surfaces. From the above results, it is clear that the increase of surface adhesion in this work is not only because of the increase of the number of oleophilic alkyl groups, but also for the reason for the increase of solid/oil contact area. The obtained surfaces with controlled oil adhesion have many potential applications, especially in the droplet-based devices.48 In recent years, such devices have shown significant advances in sample analysis and microreaction.49,50 Herein, the special tunable adhesions on our surfaces can allow them to implement many critical functions in such devices. As displayed in Figure 7, panel a, on the surface with high adhesion, arrays of microliter oil droplets (1, 2-dichloroethane, the red color of oil droplet for the addition of oil red) can be pinned on the surface without any mobility, indicating that the surface can be served as the storage media for oil droplets, which would be significant for high-throughput screening. In addition to the droplets storage, some other applications including droplet transfer (Figure 7b) and droplets mixing (Figure 7c) can also be realized through combining the high adhesive surface and the low adhesive surface. These functions would be very useful in the droplet-based microreactors and biodetection. Similar to the droplet transfer between two surfaces, the high adhesive surface can also be used to sample small volume of oil from a single oil droplet. From Figure 7, panel d, one can observe that an oil droplet was first placed on an underwater oleophobic glass substrate (with higher adhesion than the used surface), then the high adhesive surface was used to touch the droplet, and it can sample small volume of oil from the oil droplet (more information see Figure S6). This function is important and useful in some applications in which it is necessary to obtain multiple samples from one droplet for different analysis.

Figure 6. Schematic illustration of the oil/solid interactions in water. For surfaces modified with different n-alkanoic acids, the oil droplet resides in the composite interface composed with water and solid (a). For surface modified by n-alkanoic acids with short chain length, the oleophilic alkyl groups are scarce, and the oil droplet resides in the low adhesive state with little solid/oil contact area (b) because the molecular chains are scattered (c). When the chain length is increased, the number of alkyl groups increases (d), which can lead to the increase of oil-adhesive force because that the packing of molecular chains becomes denser and more ordered (e). At the same time, the solid/oil contact area is increased due to the capillary action originates from the synergistic effect between oleophilic alkyl groups and nanostructures; thus, the adhesive force is increased.

also important for the increase of adhesive force because it can result in the increase of solid/oil contact area. Taking the film modified by n-octanoic acid as the example, since the intrinsic underwater oil contact is smaller than 90° (about 80°, Figure S5), this means that the surface is underwater oleophilic. In this situation, the Wenzel equation is usually used to explain the contact angle on the rough structured surface:45

″ = r cos θow cos θow

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(2)

CONCLUSIONS In summary, a facile and novel approach was advanced to prepare tunable adhesive underwater superoleophobic surfaces based on assembling n-alkanoic acids onto the copper nanostructures. The surfaces adhesive forces can be increased from less than 1 μN to larger than 58 μN by simply increasing the chain length of used n-alkanoic acids. The increase of surface adhesive force is ascribed to the increase of both oleophilic groups and the solid/oil contact area. Noticeably, the controllability of surface adhesion is universal regardless of oil type. This paper proposed a new concept to control the underwater oil adhesion on metal surface, and we believe the simple concept reported here can easily be extended to other metals, which would open up a new perspective in regulating metal surface adhesion in water and extend the applications shown in current work, for example, antifouling, microfluidic devices, and chemical engineering materials.

Herein, r is the ratio of the actual area of the rough surface to the geometric projected area, and θ″ow and θow are the contact angles of an oil droplet on rough and smooth solid surfaces in water, respectively. Because r is always larger than 1, according to eq 2, the rough surface would be more oleophilic compared with the flat surface, which is apparently contradictory with our results (Figure 3a, superoleophobicity on our surface). Therefore, the Wenzel equation is not suitable here, and it is assumed that the oil droplet should also be in the composite Cassie state. From Figure S4, it can be found that even on the surfaces modified with long chain length molecules, the surfaces still show relatively weak hydrophobicity (the water contact angles in air are less than 120°). When these surfaces are placed into water, the interspaces between copper nanoparticles would be taken up by water under the water pressure.19,46,47 Thus, similar to those surfaces modified by short chain molecules, the oil/water/solid three-phase interface can be formed when the E


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Figure 7. Applications of the as-prepared surfaces: (a) droplets storage on the surface with high adhesion; (b) transfer oil droplet using the surface with high adhesion; (c) mixing two oil droplets between two different adhesive surfaces; (d) sampling small volume liquid (emphasized by the red circle) from one droplet assisted by the surface with high adhesion. These results indicate that our surfaces can demonstrate similar functions as shown in reference on superhydrophobic surfaces,48 while advancing new application environment in water.

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Author Contributions

ASSOCIATED CONTENT

S Supporting Information *

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Zhongjun Cheng and Hongwei Liu contributed equally.

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.5b06374. XRD of copper film; dependence of underwater oil contact angles on sputtering time; AFM images of film after modification with n-alkanoic acid; dependence of water and oil contact angles on chain length of n-alkanoic acids; dependence of underwater oil contact angles on chain length of n-alkanoic acids on flat copper films; droplet splitting results for surfaces modified with different n-alkanoic acids (PDF)

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Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS

This work is supported by the National Natural Science Foundation of China (NSFC Grant No. 21304025), the Fundamental Research Funds for the Central Universities (Grant No. HIT.IBRSEM.A.201408), the Research Fund for the Doctoral Program of Higher Education of China (20112302120062), and the assisted project by Heilong Jiang Postdoctoral Funds for scientific research initiation (LBHQ13063).

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Phone: (+86) 045186412153. Fax: (+86) 045186412153. F


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(22) Chen, L.; Liu, M.; Bai, H.; Chen, P.; Xia, F.; Han, D.; Jiang, L. Antiplatelet and Thermally Responsive Poly(N-isopropylacrylamide) Surface with Nanoscale Topography. J. Am. Chem. Soc. 2009, 131, 10467−10472. (23) Liu, W.; Liu, X.; Fangteng, J.; Wang, S.; Fang, L.; Shen, H.; Xiang, S.; Sun, H.; Yang, B. Bioinspired Polyethylene Terephthalate Nanocone Arrays with Underwater Superoleophobicity and AntiBioadhesion Properties. Nanoscale 2014, 6, 13845−13853. (24) Xue, Z.; Wang, S.; Lin, L.; Chen, L.; Liu, M.; Feng, L.; Jiang, L. A Novel Superhydrophilic and Underwater Superoleophobic Hydrogel-Coated Mesh for Oil/Water Separation. Adv. Mater. 2011, 23, 4270−4273. (25) Zhang, L.; Zhang, Z.; Wang, P. Smart Surfaces with Switchable Superoleophilicity and Superoleophobicity in Aqueous Media: Toward Controllable Oil/Water Separation. NPG Asia Mater. 2012, 4, e8. (26) Yong, J.; Yang, Q.; Chen, F.; Bian, H.; Du, G.; Farooq, U.; Hou, X. Superoleophobic Surfaces: Reversible Underwater Lossless Oil Droplet Transportation. Adv. Mater. Interfaces 2015, 2, 1400388. (27) Su, B.; Wang, S.; Song, Y.; Jiang, L. Utilizing Superhydrophilic Materials to Manipulate Oil Droplets Arbitrarily in Water. Soft Matter 2011, 7, 5144−5149. (28) Wu, D.; Wu, S.; Chen, Q.; Zhao, S.; Zhang, H.; Jiao, J.; Piersol, J. A.; Wang, J.; Sun, H.; Jiang, L. Facile Creation of Hierarchical PDMS Microstructures with Extreme Underwater Superoleophobicity for Anti-Oil Application in Microfluidic Channels. Lab Chip 2011, 11, 3873−3879. (29) Chen, L.; Liu, M.; Lin, L.; Zhang, T.; Ma, J.; Song, Y.; Jiang, L. Thermal-Responsive Hydrogel Surface: Tunable Wettability and Adhesion to Oil at The Water/Solid Interface. Soft Matter 2010, 6, 2708−2712. (30) Huang, Y.; Liu, M.; Wang, J.; Zhou, J.; Wang, L.; Song, Y.; Jiang, L. Controllable Underwater Oil-Adhesion-Interface Films Assembled from Nonspherical Particles. Adv. Funct. Mater. 2011, 21, 4436−4441. (31) Cheng, Q.; Li, M.; Yang, F.; Liu, M.; Li, L.; Wang, S.; Jiang, L. An underwater pH-Responsive Superoleophobic Surface with Reversibly Switchable Oil-Adhesion. Soft Matter 2012, 8, 6740−6743. (32) Tian, D.; Guo, Z.; Wang, Y.; Li, W.; Zhang, X.; Zhai, J.; Jiang, L. Phototunable Underwater Oil Adhesion of Micro/Nanoscale Hierarchical-Structured ZnO Mesh Films with Switchable Contact Mode. Adv. Funct. Mater. 2014, 24, 536−542. (33) Dunderdale, G. J.; Urata, C.; Hozumi, A. An Underwater Superoleophobic Surface That Can Be Activated/Deactivated via External Triggers. Langmuir 2014, 30, 13438−13446. (34) Liu, M.; Nie, F.; Wei, Z.; Song, Y.; Jiang, L. In Situ Electrochemical Switching of Wetting State of Oil Droplet on Conducting Polymer Films. Langmuir 2010, 26, 3993−3997. (35) Tan, K. Y.; Hughes, T. L.; Nagl, M.; Huck, W. T. S. Nonfouling Capture−Release Substrates Based on Polymer Brushes for Separation of Water-Dispersed Oil Droplets. ACS Appl. Mater. Interfaces 2012, 4, 6403−6409. (36) Ding, C.; Zhu, Y.; Liu, M.; Feng, L.; Wan, M.; Jiang, L. PANI Nanowire Film with Underwater Superoleophobicity and PotentialModulated Tunable Adhesion for No Loss Oil Droplet Transport. Soft Matter 2012, 8, 9064−9068. (37) Manna, U.; Lynn, D. M. Synthetic Surfaces with Robust and Tunable Underwater Superoleophobicity. Adv. Funct. Mater. 2015, 25, 1672−1681. (38) Tie, L.; Guo, Z.; Liu, W. pH-Manipulated Underwater Oil Adhesion Wettability Behavior on the Micro/Nanoscale Semicircular Structure and Related Thermodynamic Analysis. ACS Appl. Mater. Interfaces 2015, 7, 10641−10649. (39) Yu, X.; Wang, Z. Q.; Jiang, Y. G.; Shi, F.; Zhang, X. Reversible pH-Responsive Surface: From Superhydrophobicity to Superhydrophilicity. Adv. Mater. 2005, 17, 1289−1293. (40) Wang, S.; Feng, L.; Liu, H.; Sun, T.; Zhang, X.; Jiang, L.; Zhu, D. Manipulation of Surface Wettability between Superhydrophobicity and Superhydrophilicity on Copper Films. ChemPhysChem 2005, 6, 1475−1478.

REFERENCES

(1) Liu, M.; Wang, S.; Wei, Z.; Song, Y.; Jiang, L. Bioinspired Design of a Superoleophobic and Low Adhesive Oil/Water Interface. Adv. Mater. 2009, 21, 665−669. (2) Waghmare, P. R.; Gunda, N. S. K.; Mitra, S. K. Under-water Superoleophobicity of Fish Scales. Sci. Rep. 2014, 4, 7454. (3) Xu, L.; Peng, J.; Liu, Y.; Wen, Y.; Zhang, X.; Jiang, L.; Wang, S. Nacre-Inspired Design of Mechanical Stable Coating with Underwater Superoleophobicity. ACS Nano 2013, 7, 5077−5083. (4) Liu, X.; Zhou, J.; Xue, Z.; Gao, J.; Meng, J.; Wang, S.; Jiang, L. Clam’s Shell Inspired High-Energy Inorganic Coatings with Underwater Low Adhesive Superoleophobicity. Adv. Mater. 2012, 24, 3401− 3405. (5) Callow, J. A.; Callow, M. E. Trends in the Development of Environmentally Friendly Fouling-Resistant Marine Coatings. Nat. Commun. 2011, 2, 244. (6) Xu, L.; Zhao, J.; Su, B.; Liu, X.; Peng, J.; Liu, Y.; Liu, H.; Yang, G.; Jiang, L.; Wen, Y.; Zhang, X.; Wang, S. An Ion-Induced Low-OilAdhesion Organic/Inorganic Hybrid Film for Stable Superoleophobicity in Seawater. Adv. Mater. 2013, 25, 606−611. (7) Lin, L.; Liu, M.; Chen, L.; Chen, P.; Ma, J.; Han, D.; Jiang, L. BioInspired Hierarchical Macromolecule−Nanoclay Hydrogels for Robust Underwater Superoleophobicity. Adv. Mater. 2010, 22, 4826−4830. (8) Liu, X.; Gao, J.; Xue, Z.; Chen, L.; Lin, L.; Jiang, L.; Wang, S. Bioinspired Oil Strider Floating at the Oil/Water Interface Supported by Huge Superoleophobic Force. ACS Nano 2012, 6, 5614−5620. (9) Jin, M.; Li, S.; Wang, J.; Xue, Z.; Liao, M.; Wang, S. Underwater Superoleophilicity to Superoleophobicity: Role of Trapped Air. Chem. Commun. 2012, 48, 11745−11747. (10) Cheng, Z.; Ding, C.; Liu, H.; Zhu, Y.; Jiang, L. A Facile Bacterial Assisted Electrochemical Self-Assembly of Polypyrrole Micro-pillars: Towards Underwater Low Adhesive Superoleophobicity. Nanoscale 2014, 6, 190−194. (11) Zhang, G.; Zhang, X.; Huang, Y.; Su, Z. A Surface Exhibiting Superoleophobicity Both in Air and in Seawater. ACS Appl. Mater. Interfaces 2013, 5, 6400−6403. (12) Sawai, Y.; Nishimoto, S.; Kameshima, Y.; Fujii, E.; Miyake, M. Photoinduced Underwater Superoleophobicity of TiO2 Thin Films. Langmuir 2013, 29, 6784−6789. (13) Ma, W.; Xu, H.; Takahara, A. Substrate-Independent Underwater Superoleophobic Surfaces Inspired by Fish-Skin and MusselAdhesives. Adv. Mater. Interfaces 2014, 1, 1300092. (14) Palamà, I. E.; D'Amone, S.; Biasiucci, M.; Gigli, G.; Cortese, B. Bioinspired Design of a Photoresponsive Superhydrophobic/oleophilic Surface with Underwater Superoleophobic Efficacy. J. Mater. Chem. A 2014, 2, 17666−17675. (15) Yong, J.; Chen, F.; Yang, Q.; Du, G.; Shan, C.; Bian, H.; Farooq, U.; Hou, X. Bioinspired Transparent Underwater Superoleophobic and Anti-oil Surfaces. J. Mater. Chem. A 2015, 3, 9379−9384. (16) Yong, J.; Chen, F.; Yang, Q.; Zhang, D.; Farooq, U.; Du, G.; Hou, X. Bioinspired Underwater Superoleophobic Surface with Ultralow Oil-Adhesion Achieved by Femtosecond Laser Microfabrication. J. Mater. Chem. A 2014, 2, 8790−8795. (17) Wang, H.; Guo, Z. Design of Underwater Superoleophobic TiO2 Coatings with Additional Photo-Induced Self-Cleaning Properties by One-Step Route Bio-Inspired From Fish Scales. Appl. Phys. Lett. 2014, 104, 183703. (18) Hejazi, V.; Nyong, A. E.; Rohatgi, P. K.; Nosonovsky, M. Wetting Transitions in Underwater Oleophobic Surface of Brass. Adv. Mater. 2012, 24, 5963−5966. (19) Palamà, I. E.; D'Amone, S.; Arcadio, V.; Caschera, D.; Toro, R. G.; Gigli, G.; Cortese, B. Underwater Wenzel and Cassie Oleophobic Behavior. J. Mater. Chem. A 2015, 3, 3854. (20) Huang, H.; Zacharia, N. S. Layer-by-Layer Rose Petal Mimic Surface with Oleophilicity and Underwater Oleophobicity. Langmuir 2015, 31, 714−720. (21) Nishimoto, S.; Bhushan, B. Bioinspired Self-Cleaning Surfaces with Superhydrophobicity, Superoleophobicity, and Superhydrophilicity. RSC Adv. 2013, 3, 671−690. G


Research Article


ACS Applied Materials & Interfaces (41) Zhu, X.; Zhang, Z.; Men, X.; Yang, J.; Xu, X. Rapid Formation of Superhydrophobic Surfaces with Fast Response Wettability Transition. ACS Appl. Mater. Interfaces 2010, 2, 3636−3641. (42) Tao, Y. T. Structural Comparison of Self-Assembled Monolayers of n-alkanoic Acids on the Surfaces of Silver, Copper, and Aluminium. J. Am. Chem. Soc. 1993, 115, 4350−4358. (43) Cassie, A. B. D.; Baxter, S. Wettability of Porous Surfaces. Trans. Faraday Soc. 1944, 40, 546−551. (44) Jung, Y. C.; Bhushan, B. Wetting Behavior of Water and Oil droplets in Three-Phase Interfaces for Hydrophobicity/Philicity and Oleophobicity/Philicity. Langmuir 2009, 25, 14165−14173. (45) Wenzel, R. N. Resistence of Solid Surfaces to Wetting by Water. Ind. Eng. Chem. 1936, 28, 988−994. (46) Marmur, A. Underwater Superhydrophobicity: Theoretical Feasibility. Langmuir 2006, 22, 1400−1402. (47) Bobji, M. S.; Kumar, S. V.; Asthana, A.; Govardhan, R. N. Underwater Sustainability of the “Cassie” State of Wetting. Langmuir 2009, 25, 12120−12126. (48) Balu, B.; Berry, A. D.; Hess, D. W.; Breedveld, V. Patterning of Superhydrophobic Paper to Control the Mobility of Micro-Liter Drops for Two-Dimensional Lab-On-Paper Applications. Lab Chip 2009, 9, 3066−3075. (49) Song, H.; Chen, D. L.; Ismagilov, R. F. Reactions in Droplets in Microfluidic Channels. Angew. Chem., Int. Ed. 2006, 45, 7336−7356. (50) deMello, A. J. Control and Detection of Chemical Reactions in Microfluidic Systems. Nature 2006, 442, 394−402.

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Regulating Underwater Oil Adhesion on Superoleophobic Copper

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