Adhesive Janus Self-Standing Films Modified with

Article pubs.acs.org/IECR

Oleophobic/Adhesive Janus Self-Standing Films Modified with Bifurcated Short Fluorocarbon Chains as Transparent Oil Stain-Free Coating with Attachability Taichi Nakashima,† Mizuki Tenjimbayashi,† Takeshi Matsubayashi,† Kengo Manabe,† Masato Fujita,‡ Takeshi Kamiya,‡ Tsunetoshi Honda,‡ and Seimei Shiratori*,† †

Center for Material Design Science, School of Integrated Design Engineering, Graduate School of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, Kanagawa 223-8522, Japan ‡ Mitsubishi Materials Electronic Chemicals Co., Ltd., 3-1-6 Barajima, Akita City, Akita 010-8585, Japan S Supporting Information *

ABSTRACT: Oil stains negatively affect the performances of our belongings and industrial equipment. However, conventional oleophobic coatings contain complex nanostructures or long fluoroalkyl chains, which are environmentally unsafe and limit their applications. In addition, the integration of film transparency, flexibility, and oleophobicity represent extremely challenging tasks. Herein, we report self-standing oleophobic/ adhesive Janus membranes with flexibility and transparency, which were composed of environmentally low impact materials: poly(vinyl alcohol) (PVA)/SiO2 nanoparticle composites modified with bifurcated short fluorocarbon chains via the sol−gel method. The optimized coating performed the oleophobicity (oleic acid sliding angle = 27.9°) and reduced more than 50% of oil adhesion on glass substrate. It also maintained its transparency (93.13% at wavelength of 550 nm) after the exposure to oil mist. Moreover, the coatings were able to attach to various substrates to provide them an oleophobicity. Our results demonstrate the important role to develop oleophobic coating materials with low environmental impact.

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INTRODUCTION Oil and its products are ubiquitous in our daily life and many industry fields; consequently, oil stains can be seen in such places as kitchen walls, factories, and smartphone surfaces. For instance, kitchen walls are easily stained by oil, which deteriorates their appearance; as a result, they require periodic cleaning. Adhesion of petroleum in factory can cause duct fire accidents. The fingerprints left on smartphone displays impair their visibility which bothers numerous people along with the recent development of electronic devices. So far, oil adhesion was removed by wiping the surface with surfactant for restoring the original appearance of kitchen wall surfaces, preventing fires caused by oil spills, and improving the visibility of smartphone displays.1 However, this approach is accompanied by energy losses and produce large amounts of disposal waste, which seriously affect the environment and biological living organisms.2 In particular, most surfactants cause the formation of heterologous organisms which obstruct the branchial respiration of fish. Alternatively, surfaces with oleophobicity have attracted much attention because of their self-cleaning abilities and liquid repellent properties, which can prevent the adhesion of oil species without energy losses.3−9 There are the following three approaches to prevent oil adhesions. The one approach is © 2017 American Chemical Society

superoleophobic coating, which is designed by nano- and microtextured hierarchical structures and the following modification of fluorocarbon materials.10−16 The oil droplets become spherical shapes to slide off on the slightly tilted surface. This surface can prevent adhesion of oil almost perfectly. Another approach corresponds to perfluorinated group end-tethered smooth surfaces.17−21 Thanks to the chemical stability and the low surface energy of fluorine compounds, the surfaces can easily remove adhesion. In addition, this coating is generally transparent because of the surface smoothness. The third approach is represented by oleophobic surfaces with long alkyl chains tethered on glass substrates, which can slide various liquids off with tilting thanks to the “liquidlike” long alkyl chain moving to parry a liquid.22 The surface also performs transparency and high chemical stability.22−24 Despite the considerable efforts, however, the challenge such as light scattering derived from rough structures, elaborate fabrication steps, its biocompatibility, and coatings on limited Received: Revised: Accepted: Published: 3928

January 14, 2017 March 14, 2017 March 22, 2017 March 22, 2017 DOI: 10.1021/acs.iecr.7b00164 Ind. Eng. Chem. Res. 2017, 56, 3928−3936

Article

Industrial & Engineering Chemistry Research

Figure 1. Structural formula of (a) DB-EOS, (b) TEOS, and (c) PVA. (d) A schematic of the adhesive oleophobic film production. The central image describes the structure of the produced Janus films, and the right image depicts the curved substrate. The top polymer layer corresponds to the oleophobic molecular layer, the middle layer contains the flexible polymer, and the bottom layer represents the substrate.

environmental impact than regulated fluorine compounds such as perfluorooctanoic acid. During film preparation, the PVA and DB−EOS components were combined by a sol−gel method in the presence of tetraethylorthosilicate (TEOS) cross-linker (Figure 1b).33−39 The resulting coating performed transparency, oleophobicity, and attach-ability to various substrates thanks to the water-induced adhesion characteristics of PVA (Figure 1c). Although the obtained film can be easily swelled in the presence of water, this problem can be alleviated by the addition of silica nanoparticles (NPs) into the PVA matrix.40−43 The structure of the membrane is shown in Figure 1d.

substrates still remain for practical use. Especially, the practical use of long fluoroalkyl chains (i.e., fluorocarbon with carbon number C ≥ 8) is forbidden by the Stockholm Convention on Persistent Organic Pollutants due to their negative environmental effects, which limits the application.25−27 Herein, we propose transparent oleophobic/adhesive “Janus” films,28,29 that the surface performs oleophobicity (low surface energy) and the back can be firmly attached to various substrates (high surface energy), with low environmental impact materials. The surface was modified with short fluoroalkyl chains (carbon number C = 4), while the other one exhibited adhesive characteristics. Poly(vinyl alcohol) (PVA) polymer was used as a substrate for the produced transparent and self-standing adhesive coatings,30−32 owing to its low costs, high solubility in water, and low environmental impact; hence it can be used in a broad range of applications. Additionally, the attachment is repeatedly available because its adhesion strength is low enough not to destroy the surface structure of the attached materials). As a surface modifier with a low environmental impact, fluoroalkyl silane DB−EOS was utilized (see Figure 1a for the structure). It contains a bifurcated structure without long fluoroalkyl chains (C = 4). Therefore, this compound is expected to have a lower

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EXPERIMENTAL SECTION Materials. Ethanol (EtOH; Kanto Chemical Co., Inc., Tokyo, Japan), HCl (Kanto Chemical Co., Inc., Tokyo, Japan), glass substrates (76 × 26 mm, thickness: 1.0 mm, refractive index: 1.51, Matsunami Glass Ind., Ltd., Kishiwada, Japan), and DB−EOS is kindly provided by Mitsubishi material Co., Inc., (Tokyo, Japan). The chemical structure is listed in Figure 1a, PVA (PD = 1500, refractive index: 1.53, Wako Chemical Co., Inc., Tokyo, Japan), TEOS (Wako Pure Chemical Industries Ltd., Osaka, Japan), water-dispersed colloidal silica (OXS,

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DOI: 10.1021/acs.iecr.7b00164 Ind. Eng. Chem. Res. 2017, 56, 3928−3936

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by ultraviolet−visible (UV−Vis) spectroscopy (UVmini−1240, Shimadzu Co., Ltd., Kyoto, Japan). In addition to investigating the effect of SiO2 NPs addition, haze values for the obtained films were measured by a haze meter (NDH−5000, Nippon Denshoku Industries, Tokyo, Japan), using a white lightemitting diode (5.0 V, 3.0 W) as an optical source. Refractive index of coatings was determined by ellipsometry (MARY-102, FiveLab Co., Ltd., Kawaguchi, Japan). Swelling Tests. During swelling testing, a water droplet was applied to the surface of each fabricated oleophobic film for 10 min, after which its thickness was evaluated by laser microscopy. Chemical bonding characteristics were investigated for each film via Fourier transform infrared (FT−IR) spectroscopy (Alpha, Bruker Corporation, Billerica). Oil Adhesion Tests. For oil adhesion testing, 30 μL of oleic acid-containing colored carbon NP solution was applied to a rubber stamp with dimensions of 1 × 1 cm. Subsequently, the treated rubber stamp was adhered to the produced coatings at a load of 500 g/cm2, and the resulting color difference was observed using a color reader (CR−13, Minolta Co., Ltd., Tokyo, Japan; see Figure S1). Oil Mist Adhesion Tests. Oil mist was produced by heating oleic acid to 150 °C. Afterward, the obtained films were exposed to the resulting vapor for 2 h, and their transmittance values were evaluated. During oil mist adhesion testing, the TEOS and DB−EOS (4.8) coatings were used (Table 1). Film Adhesion Tests. After applying water to the surface of the fabricated films, they were adhered to the walls of a glass beaker followed by the removal of water excess. Subsequently, oleic acid colored by the oil red O dye solution was dropped onto the surface of the fabricated oleophobic films. Mechanical Durability Tests. As adhesion force measurements, the fabricated films were cut into 2 × 2 cm pieces and attach to stainless steel, glass, or polystyrene plate. Then, adhesion force was measured by a tensile testing machine (EZ− S, Shimadzu Corporation, Tokyo, Japan). As abrasion tests, the fabricated films were cut into bigger (3 × 3 cm) and smaller (1× 1 cm) pieces, which were subsequently studied using the tensile testing machine.

particle diameter: 4−6 nm, refractive index: 1.50, Nissan Chemical Co., Inc., Tokyo, Japan), and oleic acid (Wako Chemical Co., Inc., Tokyo, Japan) were used for film fabrication. Polymer Layer Formation. Two grams of the colloidal solution containing PVA and SiO2 NPs [PVA/water solution = 1:9 (weight ratio), NP content: 0−25%] was spread across the surface of a glass slide. Consequently, a closely packed NPcontaining PVA layer was formed on the glass substrate after the resulting sample was dried at 100 °C for 1 h. Oleophobic Layer Formation. A mixture containing ethanol, TEOS, and DB−EOS components was stirred for 10 min; after that, HCl and water species were added to the obtained solution, which was stirred for another 30 min. (The corresponding experimental conditions are listed in Table 1, Table 1. Components Utilized for the Fabrication of the Oleophobic PVA-Based Coatings coating pure PVA TEOS DB−EOS TEOS and DB−EOS (2.9) TEOS and DB−EOS (4.8) TEOS and DB−EOS (7.2) SiO2 NPs (2.5) SiO2 NPs (5) SiO2 NPs(15) SiO2 NPs(25)

TEOS (mmol)

DB−EOS (mmol)

SiO2 NPs (mol)/PVA (mol) (%)

− 4.8 − 2.9

− − 0.3 0.3

− − − −

4.8

0.3

−

7.2

0.3

−

4.8 4.8 4.8 4.8

0.3 0.3 0.3 0.3

2.5 5 15 25

and the volume of EtOH, water, and HCl were 12.7 mL, 13.9 mmol, 0.0793 mmol, respectively, except for the pure PVA film.) The PVA film on the glass substrate prepared in the previous section was immersed into the resulting solution for 20 h and then dried at 100 °C for 1 h, and finally the film was peeled off from the glass substrate to provide the oleophobic/ adhesive Janus property. Film Thickness Measurements. Images of the PVA films on the glass substrates were obtained by laser microscopy (VK−9710 instrument, KEYENCE CORPORATION, Osaka, Japan). The resulting film thickness was measured as a difference between the total thickness of the sample and that of the glass substrate. Contact Angles and Sliding Angle Measurements. A droplet containing 10 μL of water or oleic acid was dropped onto each fabricated coating. The corresponding equilibrium contact angles and sliding angles were measured using a contact angle meter (CA−DT, Kyowa Interface Science Co., Ltd., Niza, Japan), and the contact angle hysteresis was measured by increasing and decreasing the droplet volume to extract the advancing and receding contact angles. Surface Chemistry and Morphology Measurements. X-ray photoelectron spectroscopy (XPS, JPS-9010TR, JEOL Ltd., Musashino, Japan) was used to investigate the difference of wettability and the chemical composition of the surface. Atomic force microscope (SPM-9500 J2, Shimadzu Co., Ltd., Kyoto, Japan) is used to investigate the surface morphology. Film Transmittance Measurements. All coatings were first applied to the glass substrate and measured transmittance

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RESULTS AND DISCUSSION Effect of TEOS and DB-EOS Addition on Film Wettability. In this section, the effect of the TEOS and DBEOS addition on wettability of the produced PVA films was investigated. Figure 2a shows the contact angles obtained for each surface, which were systematically higher for the DB− EOS-containing films, indicating that the bifurcated fluorocarbon groups of DB−EOS decreased the film surface energy.40 In addition, the magnitudes of the contact angle obtained for the TEOS-modified surfaces were also higher than that for the pure PVA film because the methyl groups of TEOS produced a similar effect.41,42 However, since the addition of fluorocarbon groups resulted in lower surface energies (as compared to the surfaces modified with only methyl groups), the coatings containing DB−EOS species were characterized by the higher contact angles. At the same time, the PVA films modified only with DB−EOS exhibited lower contact angles of both water and oleic acid as compared to those measured for the surfaces containing both the TEOS and DB−EOS components (indicating that the DB−EOS-induced reaction was milder than the process initiated by both the TEOS and DB−EOS modifiers). Therefore, TEOS addition is necessary for fabricating a flat coating surface. A comparison between the 3930


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Figure 2. (a) Contact angles, (b) sliding angles, (c) advancing (Adv.) and receding (Rec.) contact angles, and (d) contact angle hysteresis of water measured for the produced oleophobic films with different TEOS, DB−EOS, and SiO2 NPs contents.

resulting NPs aggregates, leading to poor film visibility properties. Therefore, colloidal SiO2 NPs must be used for this purpose, owing to their small sizes (less than the light wavelength) and the absence of particle aggregation. The observed effect of the SiO2 NPs addition on the film contact angle was small, and all coating with the NP contents ranging from 2.5 to 25 mol % were characterized by the low surface energies (Figure 2a). As well as the contact angles, virtually no differences in the oleic acid sliding angle were observed for the NPs-modified PVA coatings (Figure 2b). Figure 2 (panels c and d) shows the advancing contact angle, receding contact angle, and contact angle hysteresis on the coating surfaces. These results exhibit TEOS + DB-EOS (4.8) is the best condition in terms of hydrophobicity for this fabricated coating. SiO2 NPs have a negative effect for droplet pinning due to the increase of RMS by SiO2 NPs (Figure 3a), whereas the SiO2 NPs work positively to slide a large volume droplet off the surface. The difference between contact angle hysteresis and sliding angle are probably because the hygroscopic property of PVA, which varies with droplet volume and the contact time, influences wettability, being varied with droplet volume and contact time. Surface Topography and Chemical Characteristics. The sliding angle measured for the TEOS and DB−EOS (7.2) sample was greater than that obtained for the TEOS and DB− EOS (4.8) one (Table 1 and Figure 2b). The corresponding AFM images shown in Figure 3a indicate that the RMS roughness of the resulting film increases with the amount of

DB−EOS-modified films with the coatings containing both the TEOS and DB−EOS species revealed that TEOS was an important cross-linking component. If the amount of TEOS is low, the bonding between TEOS and DB-EOS becomes weaker. As a result, the surface with a low TEOS content would not be uniformly covered with DB−EOS. Figure 2b shows the results of the sliding angle measurements performed for fabricated films, indicating that all obtained oleophobic film samples except NPs(2.5) and NPs(5) were unable to slide a water droplet. Due to the hygroscopic property of PVA, PVA film swells by absorbing water (Figure S2). The lowest value of the oleic acid sliding angle was obtained for the TEOS-modified coating (Figure 2b). Previous studies reported that alkyl-chain tethered surfaces enhanced their oleophobicity by adding the TEOS because TEOS had worked to expand the space of alkyl-chain resulting in the enhancement of alkyl chain movement.22,24 Therefore, the molecular chains tethered surface with TEOS could lead to enhance the liquid repellency. However, the TEOS-coated PVA surfaces were characterized by the relatively low contact angles and cannot repel low surface tension liquids of hexadecane and octane; therefore, they did not exhibit noticeable oleophobic abilities, and fluorine compound is required for repelling low surface tension liquid.43 Oleophobic films can experience swelling due to the water interaction with PVA; their water resistance can be enhanced by the addition of SiO2 NPs.44−47 However, this process is often accompanied by the increase in the light scattering from the 3931


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Figure 3. (a) AFM images obtained for the PVA oleophobic films with various ratios between the TEOS, DB−EOS, and SiO2 NP components. (b) Chemical elements covering the surface of the coatings and (c) molar ratios between the Si and F contents determined via XPS measurements. (d) FT-IR spectra recorded for the unmodified PVA film and PVA coating containing 5 mol % of SiO2 NPs. (e) FT-IR separated spectra of PVA film with 5 mol % of SiO2 NPs and the spectra of pure PVA.

Figure 4. (a) UV−vis spectra recorded for the PVA oleophobic films with various TEOS, DB−EOS, and SiO2 NP contents. (b) Haze parameters obtained for the oleophobic films with different contents of colloidal SiO2 NPs (here T.T. is the total transmittance, P.T. is the parallel light transmittance, and DIF is the diffusion factor).

TEOS to change the wettability. The optimized contents of the TEOS and DB−EOS components in the modified PVA films

correspond to the sample with 4.8 mmol of TEOS. The RMS of SiO2 NPs (25) is the largest, and all SiO2 NPs content film 3932


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Figure 5. (a) Color differences observed during oil adhesion testing. (b) Transmittance of the glass and NPs (5) samples before and after oil mist testing. (c) A schematic illustration of the transmission increase mechanism.

has larger RMS than TEOS + DB-EOS (4.8). It causes the decrease of oleophobicity (Figure 2d). Figure 3b shows the XPS spectra recorded for the coatings with different relative amounts of TEOS and DB−EOS, indicating that the relative F content increased at higher TEOS amounts. It can be seen from the F/Si molar ratio as shown in Figure 3c. Therefore, the lower the TEOS content, the smaller is the contact angle value of both oleic acid and water because of the nonuniformity of the resulting F layer. The effect of the SiO2 NPs in PVA was also investigated by FT−IR spectroscopy (Figure 3, panels d and e). The obtained IR peak positions were consistent with the magnitudes previously reported in the literature.47 The original PVA matrix did not include any carbonyl (CO) groups; however, the corresponding IR peaks could result from the vinyl acetate species produced from PVA via saponification. The intensities of the IR peaks attributed to the hydroxyl (O−H), methyl (C− H), and carbonyl (CO) groups were not changed after the addition of SiO2 NPs. However, the peak corresponding to C− O stretching was affected by the added SiO2 NPs, and that obtained for siloxane species remained almost the same. Generally, PVA reacts with other species via its hydroxyl groups. The difference of this result is the only peak value of C−O binding and Si−O binding. Thus, the chemical reaction is not caused by PVA and SiO2 NPs. A fabricated film with SiO2 NPs enhances topological constraints. The constraints restrict the swelling of the polymer network. Both PVA and the SiO2 NPs contain highly polar hydroxyl groups, which enhance intermolecular forces and thus increase the film water resistance (Figure S2).48 Relationship between Film Transmittance and Modifier Content. The UV−vis spectra displayed in Figure 4a show that the coating modified only with DB−EOS is characterized by the lowest transmittance value due to the presence of white DB−EOS aggregates, which preclude light penetration, while

the addition of TEOS decreases the degree of light scattering. The obtained results suggest that the added TEOS species serve as the cross-linker for the PVA and DB−EOS molecules. The transmittance of the TEOS-modified coating is almost identical to that of the pure PVA substrate, which can be explained by the chemical transformation of TEOS molecules into SiO2 species characterized by the magnitudes of refractive index similar to those of PVA and the glass substrate. According to the Fresnel equation described below, a larger difference between the refractive indices of two media na and nb increases light reflection R and, therefore, decreases its transmission T.49,50 ⎛ na − nb ⎞2 R=1−T=⎜ ⎟ ⎝ na + nb ⎠

(1)

The calculated transmittance of the unmodified PVA film was 96.0%, while the transmittance value obtained for the oleophobic coating was equal to 95.6%. The measured transmittance magnitudes for the PVA film and TEOS and DB−EOS (4.8) sample at a wavelength of 550 nm were 90.42% and 90.11%, respectively. The obtained difference between the experimental and calculated data was relatively large because only light reflectance was taken into account during calculations, while both PVA and the glass substrate could also absorb light. Since both the PVA and the TEOS modifier did not decrease light transmittance, the corresponding coatings exhibited excellent visibility properties. The transmittance of the coatings containing both the TEOS and DB−EOS species was larger than that of the PVA film. In accordance with the results of the ellipsometry measurements, their refractive index was equal to 1.41, while the corresponding transmittance was 97.0% (for comparison, the experimental transmittance measured at a wavelength of 550 nm was 93.13%). The observed discrepancy between the measured and calculated results was due to the light absorption by PVA and 3933


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Figure 6. (a) A schematic illustration of the adhesive layer fabrication process. (b) Tensile testing of the produced oleophobic films with different contents of colloidal SiO2 NPs (the sample size was 1 × 1 cm). (c) Adhesion force between SiO2 NPs (5) and each surface. (d) Oleophobic properties of the fabricated film [SiO2 NPs (5)] demonstrated by adhering it to the curved glass surface.

films, as indicated by the color change equal to 1.7 (according to the earlier study, a human eye is not capable of detecting a variation of the color difference lower than 3).51 Therefore, the addition of SiO2 NPs did not significantly affect the film antifouling properties. Since the rough structure of SiO2 NPs could trap oil droplets, the observed color difference ΔE increased. The results of the conducted oil mist tests are shown in Figure 5b. The transmittance of glass decreased after oil mist testing due to its oleophilic nature. (The exposure to oil vapor causes the formation of large oil droplets. As a result, the related transmittance magnitude decreases.) On the other hand, the fabricated film exhibited oleophobicity, which allow easy removal of large oil droplets from the film surface. Smaller oil droplets are much harder to remove, but their presence does not significantly affect the scattering properties, while they can be converted to larger ones via coalescence (Figure 5c). The obtained results suggest that the fabricated oleophobic film prevents the adhesion of stains caused by the exposure to oil mist and maintains its visible transparency. The fabricated films are capable of adhering to the substrate as explained in Figure 6a. In addition, the results of the tensile testing of the oleophobic films indicate that all tested samples exhibited flexibility properties (Figure 6b). The addition of TEOS and DB−EOS modifiers increased film elongation at the same tension load, while the presence of SiO2 NPs in the PVA matrix increased film flexibility but decreased the maximum tension load. Figure 6c shows adhesion force measurements of the fabricated film. This film can adhere to glass, stainless, polystyrene, and other surfaces. The adhesion force of this film is not strong, and the adhered surface is not broken, which indicates that this film can adhere and be peeled several times. Figure 6d describes the adhesion properties of the fabricated PVA film containing 5 mol % of SiO2 NPs. The obtained

the glass substrate. Thus, the produced oleophobic layer was characterized by the low refractive index and high transmittance, which decreased light reflection and enhanced the film visibility properties. The increase in the SiO2 NPs content decreases film transmittance. Large contents of SiO2 NPs lead to their aggregation because their intermolecular interactions become stronger than the interactions between the SiO2 NPs and the PVA species. As a result, the roughness of the oleophobic film increases the light scattering from the film surface. The added SiO2 NPs increased haze and decreased parallel transmittance of the films (Figure 4b). If the amount of the haze change is below 1%, it is most likely due to the machining accuracy (ISO 14782). The NPs (2.5) film exhibited the haze value, which was 0.23% larger than that for PVA, while the haze for NPs (15) was 1.65% larger than that for PVA. When the amount of added SiO2 NPs is in the range of 2.5−5 mol %, the corresponding haze values increase by about 1%. At a SiO2 NPs content of 5%, the related magnitudes of the total transmittance (T.T.) and the parallel transmittance (P.T.) were equal to 91.30% and 88.69%, respectively, which were lower than the value measured for the film without SiO2 NPs [TEOS and DB−EOS (4.8)] by 0.67% and 2.16%, respectively. The obtained results indicate that the films with the SiO2 NPs performed their high transparency. However, they also indicate that the addition of NPs decreased the film transmittance. Oil Adhesion Characteristics. After the rubber stamp treated with black colored oil was attached to the glass and PVA samples (Figure S1), the observed color difference was quite large due to the oleophilic nature of these two materials (Figure 5a). However, the fabricated films exhibited a significantly less intense color change after oil adhesion (since oil could be easily removed from their surfaces due to the film oleophobicity). The NP addition lowered the transmittance of the resulting 3934


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(3) Li, F.; Du, M.; Zheng, Q. Dopamine/Silica Nanoparticle Assembled, Microscale Porous Structure for Versatile Superamphiphobic Coating. ACS Nano 2016, 10, 2910−2921. (4) Stachewicz, U.; Bailey, R. J.; Zhang, H.; Stone, C. a.; Willis, C. R.; Barber, A. H. Wetting Hierarchy in Oleophobic 3D Electrospun Nanofiber Networks. ACS Appl. Mater. Interfaces 2015, 7, 16645− 16652. (5) Tuteja, A.; Choi, W.; Ma, M.; Mabry, J. M.; Mazzella, S. a; Rutledge, G. C.; McKinley, G. H.; Cohen, R. E. Designing Superoleophobic Surfaces. Science 2007, 318, 1618−1622. (6) Manabe, K.; Kyung, K. H.; Shiratori, S. Biocompatible Slippery Fluid-Infused Films Composed of Chitosan and Alginate via Layer-byLayer Self-Assembly and Their Antithrombogenicity. ACS Appl. Mater. Interfaces 2015, 7, 4763−4771. (7) Brown, P. S.; Atkinson, O. D. L. A.; Badyal, J. P. S. Ultrafast Oleophobic-Hydrophilic Switching Surfaces for Antifogging, SelfCleaning, and Oil-Water Separation. ACS Appl. Mater. Interfaces 2014, 6, 7504−7511. (8) Masheder, B.; Urata, C.; Hozumi, A. Transparent and Hard Zirconia-Based Hybrid Coatings with Excellent Dynamic/thermoresponsive Oleophobicity, Thermal Durability, and Hydrolytic Stability. ACS Appl. Mater. Interfaces 2013, 5, 7899−7905. (9) Manabe, K.; Matsubayashi, T.; Tenjimbayashi, M.; Moriya, T.; Tsuge, Y.; Kyung, K. H.; Shiratori, S. Controllable Broadband Optical Transparency and Wettability Switching of Temperature-Activated Solid/Liquid-Infused Nanofibrous Membranes. ACS Nano 2016, 10, 9387−9396. (10) Ellinas, K.; Pujari, S. P.; Dragatogiannis, D. A.; Charitidis, C. A.; Tserepi, A.; Zuilhof, H.; Gogolides, E. Plasma Micro-Nanotextured, Scratch, Water and Hexadecane Resistant, Superhydrophobic, and Superamphiphobic Polymeric Surfaces with Perfluorinated Monolayers. ACS Appl. Mater. Interfaces 2014, 6, 6510−6524. (11) Zhang, S.; Lu, F.; Tao, L.; Liu, N.; Gao, C.; Feng, L.; Wei, Y. Bio-Inspired Anti-Oil-Fouling Chitosan-Coated Mesh for Oil/water Separation Suitable for Broad Ph Range and Hyper-Saline Environments. ACS Appl. Mater. Interfaces 2013, 5, 11971−11976. (12) Zhang, G.; Zhang, X.; Li, M.; Su, Z. A Surface with Superoleophilic-to-Superoleophobic Wettability Gradient. ACS Appl. Mater. Interfaces 2014, 6, 1729−1733. (13) Steele, A.; Bayer, I.; Loth, E. Inherently Superoleophobic Nanocomposite Coatings by Spray Atomization. Nano Lett. 2009, 9, 501−505. (14) Li, L.; Breedveld, V.; Hess, D. W. Design and Fabrication of Superamphiphobic Paper Surfaces. ACS Appl. Mater. Interfaces 2013, 5, 5381−5386. (15) Xiong, L.; Kendrick, L. L.; Heusser, H.; Webb, J. C.; Sparks, B. J.; Goetz, J. T.; Guo, W.; Stafford, C. M.; Blanton, M. D.; Nazarenko, S.; Patton, D. L. Spray-Deposition and Photopolymerization of Organic-Inorganic Thiol-Ene Resins for Fabrication of Superamphiphobic Surfaces. ACS Appl. Mater. Interfaces 2014, 6, 10763− 10774. (16) Manabe, K.; Nishizawa, S.; Kyung, K. H.; Shiratori, S. Optical Phenomena and Antifrosting Property on Biomimetics Slippery FluidInfused Antireflective Films via Layer-by-Layer Comparison with Superhydrophobic and Antireflective Films. ACS Appl. Mater. Interfaces 2014, 6, 13985−13993. (17) Urata, C.; Masheder, B.; Cheng, D. F.; Hozumi, A. A Thermally Stable, Durable and Temperature-Dependent Oleophobic Surface of a Polymethylsilsesquioxane Film. Chem. Commun. 2013, 49, 3318− 3320. (18) Urata, C.; Masheder, B.; Cheng, D. F.; Hozumi, A. Unusual Dynamic Dewetting Behavior of Smooth Perfluorinated Hybrid Films: Potential Advantages over Conventional Textured and Liquid-Infused Perfluorinated Surfaces. Langmuir 2013, 29, 12472−12482. (19) Park, J.; Urata, C.; Masheder, B.; Cheng, D. F.; Hozumi, A. Long Perfluoroalkyl Chains Are Not Required for Dynamically Oleophobic Surfaces. Green Chem. 2013, 15, 100.

material undergoes moderate swelling and produces a sticky layer after application of a water droplet. Since the fabricated film exhibits high flexibility, it can easily adhere to the curved glass substrate. Hence, the produced oleophobic films can be attached to various surfaces.

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CONCLUSION In this study, transparent Janus oleophobic/adhesive films, which can be applied to various curved surfaces, have been manufactured from environmentally lower impact materials. Introduction of SiO2 NPs into the films enhanced the waterresistance on the oleophobic side without significantly impairing its transmittance, flexibility, and oleophobicity. The presence of bifurcated fluorine chains, DB-EOS, improved the surface wettability with the large contact angles and small sliding angles, which allowed fast removal of oil and water species. Thanks to its flat surface structure, in addition, the films prevented oil adhesion and oil mist adhesion, and maintained their transparency. Oleophobic surface is useful for our lives; however, various problems related to their biocompatibility and transparency properties as well as substrate usage currently exist. Owing to its transparency and adhesion characteristics, our films can bestow oleophobicity onto various surfaces.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.7b00164. Laser microscopy images obtained for the omniphobic films with various content of colloidal silica (SiO2) NPs; schematic image of definition of color difference and method of antifouling test (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Kengo Manabe: 0000-0002-8601-8003 Seimei Shiratori: 0000-0001-9807-3555 Author Contributions

T.N. conceived, designed, and carried out the experiments and analyzed the data. T.N., M.T., and K.M. wrote the paper. M.T., T.M., and K.M. provided experimental support and support in data analysis. M.F., T.K., T.H., D.T., and S.S. gave scientific advice. S.S. commented on the manuscript and supervised this project. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We appreciate very much the support from Drs. Yoshio Hotta, Kouji Fujimoto, and Kyu-Hong Kyung, whose attentive comments were a great help.

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REFERENCES

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