Inkjet Printing Enabled Controllable Paper Superhydrophobization

Research Article Cite This: ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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Inkjet Printing Enabled Controllable Paper Superhydrophobization and Its Applications Yue Zhang,†,§ Tingting Ren,†,‡,§ and Junhui He*,† †

Functional Nanomaterials Laboratory, Center for Micro/Nanomaterials and Technology and Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Zhongguancundonglu 29, Haidianqu, Beijing 100190, China ‡ University of Chinese Academy of Sciences, Beijing 100864, China S Supporting Information *

ABSTRACT: Papers’ intrinsic interconnected porous structures and hydrophilic properties usually results in difficulty and complexity in partial functionalization and regulation processes because the capillary effect may lead to the fast diffusion of modifiers from one side to the other. Here, we report a simple and innovative inkjet printing approach that led to precise hydrophobic functionalization controllable in both planar and steric dimensions. Fabrication of Janus superwetting papers and superwettable patterned papers with high precision was achieved by computer-controlled inkjet printing. Elaborate controls of ink quantity enabled superhydrophobic functionalization on one side of the paper substrate, with the opposite side superhydrophilic. Static water contact angles up to 154° were obtained on the inkjet-printed side of the paper, thanks to an appropriate combination of surface chemistry with dual-scale surface roughness. Furthermore, paper-based microfluidics were fabricated and the resolution of which were estimated to be ca. 600 μm. Meanwhile, a paper-based analytical device for colorimetric sensing of Ni(II) was designed and demonstrated based on superwettable patterned papers by inkjet printing. The inkjet printing approach reported here represents a key step forward in fabricating Janus materials and complicate patterns for practical applications. KEYWORDS: Janus paper, paper superhydrophobization, paper-based superwettable patterns, paper-based analytical devices, inkjet printing

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INTRODUCTION Surfaces with a static water contact angle (WCAs) higher than 150° are generally defined as superhydrophobic surfaces.1,2 In recent years, superhydrophobic surfaces have shown prospects in applications such as self-cleaning,1,3 anticorrosion,4 lossless liquid transfer,5 lab-on chip system,6 oil/water separation,7 and so on. Association of roughness and hydrophobic functionalization is necessary to produce superhydrophobic surfaces. Our group constructed superhydrophobic coatings by layer-by-layer self-assembly and spray-coating approaches, respectively.8,9 In other methods, transparent superhydrophobic coatings were constructed by spraying mixtures of silica and fluoropolymer nanoparticles.10,11 In these systems, the nanoparticles formed micro- and nano-roughness, and the fluoropolymer provided low-energy materials for the surface. While extensive investigations have been performed on the preparation of superhydrophobic surfaces, fewer studies have reported the fabrication of Janus wetting surfaces with high wettability contrast, namely, superhydrophobicity on one side and superhydrophilicity on the other side. Airoudj et al.12 developed a Janus wetting textile via fabrication of functional polymer coatings by plasma polymerization. The Janus © XXXX American Chemical Society

wettability endows the textile with simultaneous liquidrepellency and breathability. Besides, Janus cotton fabrics were generated by combination of selective copolymer crosslinking and sol−gel chemistry approach.13 The as-prepared Janus fabrics functioned well as filters for separation of oil from various oil/water mixtures as well as oil-in-water emulsions. Apart from the fact that few processes can be easily applied to the fabrication of paper-based Janus wetting surfaces, even less could lead to the preparation of paper-based superwettable patterns, which is of great significance for scientific research and applications in the area of lab-on-paper (i.e., paper-based devices). Lab-on-paper has demonstrated potential applications in analytical and biomedical fields because of the paper’s inexpensive, versatile, and easy post-treatment characteristics.14 Alternation of paper’s wettability is beneficial to sample storage, transport, and mixing facilitating fabrication of high-performance paper-based analytical devices (PADs).15−17 To prepare wettability patterned papers, past methods have invoked wax Received: January 21, 2018 Accepted: March 15, 2018

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DOI: 10.1021/acsami.8b01133 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

ACS Applied Materials & Interfaces

hexane was used to investigate the interfacial floating property of the Janus paper. Evaluation of the Durability of Surface Coatings. The printed Janus paper was exposed to severe physical insults (i.e., sand impact and bending cycles) to evaluate the durability of its superhydrophobicity. Regular measurements of static WCAs were performed to monitor the evolution of coating properties along with bending cycles and the sand impact test. The bending test was performed by hand at a bending radius of 7 mm with repeated bending cycles of 300. For the sand impact test, the Janus paper under investigation was tilted by 45° and impacted by 40 g of sand particles with diameters of 100−350 μm. The sand particles flowed out of a steel funnel 100 cm above the substrate surface in 60 s corresponding to an impinging energy of 0.4 J. SEM and optical microscopy were used to characterize the morphologies of the Janus paper before and after the sand impact test.

printing,18 photolithography,19 and plasma processing,20 and so forth. Nevertheless, wide applications of these approaches are limited by either low wettability contrast or sophisticated equipment requirement. Generally, papers possess intrinsic interconnected porous structures and hydrophilic properties. This usually results in difficulty and complexity in partial functionalization and regulation processes because the capillary effect may lead to the fast diffusion of modifiers from one side to the other. Therefore, more efforts need to be devoted to research on Janus membranes and superwettable patterns, including their easy fabrication as well as innovative applications. Inkjet printing has been recognized as a well-established and versatile patterning technology because of its outstanding designability, controllability, suitability for mass production, and capability to precisely deposit picoliter volumes of ink droplets. However, the employment of inkjet printing has been rarely reported for controllable paper superhydrophobization.21 Herein for the first time, inkjet printing was elaborately adopted to realize facile constructions of paper-based superwettable Janus surfaces and patterns with nanoscale surface roughness, on the basis of which fabrication and conceptual demonstration of a PAD for Ni(II) analysis were described as well.

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RESULTS AND DISCUSSION The hydrolysis−condensation of TEOS and POTS under acidic solution induced the generation of hydrophobic precursors. In our previous work, the filter paper was simply soaked with the hydrophobic precursor and the WCAs of obtained hydrophobic paper were smaller than 150° because of the shortage of nanoscale roughness.6 In the current work, inkjet printing was used to generate nanoscale roughness on the filter paper surface to enhance hydrophobicity. As described in Figure 1, the hydrophobic precursor was inkjet-printed onto one side of filter papers through 1−3 printing passes, generating Janus papers.

MATERIALS AND METHODS

Tetraethyl orthosilicate (TEOS, 98+%) and 1H,1H,2H,2H-perfluorooctyltriethoxysilane (POTS, 97%) were purchased from Alfa Aesar. Ethanol (99.5%), n-hexane, hydrochloric acid (36%), rhodamine B, copper sulfate, and nickel nitrate were obtained from Beihua Fine Chemicals. Dimethylglyoxime (DMG) was purchased from TCI, Shanghai. All reagents were used as received unless otherwise stated. Filter paper (#103) with an average thickness of 90.4 μm and a syringe filter (0.22 μm) were obtained from Hangzhou Xinxing Paper Limited and Lanyi Chemicals, respectively. Epson Stylus Photo R330 was used to inkjet print the hydrophobic precursor onto the filter paper, which was cut into pieces of 13 cm × 13 cm. Blank ink cartridges were purchased from CaiTianXia flagship estore. Hydrophobic Precursor Preparation. The hydrophobic precursor was prepared following our previous reports with slight modifications.6,22 Specifically, 24 mL of absolute ethanol was mixed with 1−2 mL of water and 3 μL of hydrochloric acid (36%). The mixture was stirred for 1 min, followed by the addition of 0.5−2 mL of TEOS and 1.5 mL of POTS dropwise successively. After magnetic stirring at room temperature for 24 h, the hydrophobic precursor was obtained and stored under relatively dry conditions. Fabrication of Janus Paper and Superwettable Patterns by Inkjet Printing. Prior to inkjet printing, cartridges containing commercial washing liquid were loaded into ink bin, and the “nozzle cleaning” program was carried out to clean the printing nozzles. The hydrophobic precursor was first filtrated by a 0.22 μm syringe filter and injected into the blank ink cartridge. The hydrophobic precursor was inkjet-printed onto one side of filter papers through 1−3 printing passes to prepare Janus wetting papers. Paper-based hydrophobic− hydrophilic patterns were first drawn by using the SolidWorks software and then fabricated by inkjet printing the hydrophobic precursor onto the superhydrophilic side of as-prepared Janus paper. After inkjet printing, all papers were heated for 1 h in an oven at 60 °C prior to testing. Characterization of Janus Paper and Superwettable Patterns. The morphologies of pristine and printed filter papers were observed by scanning electron microscopy (SEM, Hitachi S4800), atomic force microscopy (AFM, NTEGRA Solaris), and optical microscopy (OPTPRO2008). The WCAs of all surfaces were measured at room temperature (20 °C) on a Kino SL200B/K automatic contact angle meter using a 4 μL deionized water droplet as the liquid probe. A mixture of CuSO4-dyed deionized water and n-

Figure 1. Filter papers were functionalized controllably via inkjet printing exhibiting Janus wetting properties.

The surface wettability of the inkjet-printed paper was investigated by WCA measurements. Figure 2 presents the static WCA measurements that were performed on both sides of the paper after each inkjet printing pass. Hydrophobic functionalization leads to a superhydrophobic surface on account of recorded WCAs higher than 150°. Because of the small quantity of ink jetted by each printing pass, the hydrophobic precursor was printed mostly on the top half of the paper. This realizes precise partial functionalization of a paper, making one surface superhydrophobic and the other remaining superhydrophilic. Controllable loading of hydrophobic precursor is vital for the preparation of Janus paper by the inkjet printing approach. It should be noted that, even after three printing passes, the back side of the paper remains superhydrophilic. According to SEM cross-sectional views (Figure S1), the paper thickness slightly increased as the number of printing pass increased. B


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Figure 2. (A) WCAs and the corresponding images of water droplets on pristine and inkjet-printed papers with various printing passes. (B) Water droplet (dyed with rhodamine B) on the pristine area and the inkjet-printed (by one printing pass) area of the paper. (C) Water (dyed with CuSO4) flowing down from the superhydrophobic surface prepared by three printing passes. (D) Various droplets on the superhydrophobic surface prepared by three printing passes.

Figure 3. SEM images and illustrations of pristine paper (A,E,I) and inkjet-printed papers by one (B,F,J), two (C,G,K), and three (D,H,L) printing passes.

Generally speaking, surfaces with a static WCA higher than 150° are defined as superhydrophobic surfaces. Cassie and Wenzel wetting states are two main superhydrophobic states on a rough surface.2 Cassie’s state exhibits a very low WCA hysteresis. The water droplet adopts a non-wet-contact mode in Cassie’s state and easily rolls off the solid surface.23 By contrast, the superhydrophobic surface in Wenzel’s state is adhesive and exhibits a high WCA hysteresis. The water droplet pins the solid surface in a wet-contact mode and hardly slides.24 To further reveal the wetting states of the Janus paper, the water droplet status on the tilted inkjet-printed surface was tested. As shown in Figure S4, the water droplet pinned the superhydrophobic surface even after the Janus paper was tilted at 40°. This indicates that the superhydrophobic surface of the Janus paper is in Wenzel’s state. SEM images of pristine paper and inkjet-printed papers were taken to examine if morphology changes had occurred upon inkjet printing. As shown in Figure 3, filter papers possess an intrinsic microscale structure and porosity. The cellulose fibers of pristine paper have a relatively smooth appearance. Compared with pristine paper, the fiber roughness of inkjetprinted papers was significantly enhanced. Notably, inkjet printing of a hydrophobic precursor endows filter papers with nanostructured roughness. Increasing the printing pass of the hydrophobic precursor leads to the generation of more tiny

nanonipples, which was indicated by AFM observations as well (Figure S5). Because few nanoparticles in the hydrophobic precursor were observed by high-resolution TEM. The nanoscale roughness is mainly generated by the small inkdroplet jetted. According to the manufacturer’s description of the inkjet printer, each inkdroplet jetted by the printer is only 1.5 pL. Moreover, during the deposition process of the inkdroplet to the paper substrate, the solvent of the ink (e.g., ethanol) volatilizes, leading to the condensation of the hydrophobic polymer and generation of nanoscale roughness. As indicated in Figure 3G,K, paper fibers are thoroughly coated by hydrophobic modifier after two printing passes. This dense superhydrophobic coating will prevent the hydrophobic precursor further loaded by the third inkjet pass from penetrating into the paper. Although the fibers in Figure 3G,K and 3H,L appear as lower roughness outwardly compared with that in Figure 3F,J, more hydrophobic precursor loading through increasing inkjet pass facilitates thorough hydrophobic functionalization of paper fibers. This is consistent with the WCA measurements in Figure 2. Hydrophobic functionalization associated with hierarchical (both microscale and nanoscale) roughness endows the paper surface with superhydrophobicity. Additionally, the interfacial stability associated with the asprepared Janus paper was investigated with an oil/water C


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the superhydrophobic surface of the Janus paper upon bending cycles. The superhydrophobicity was unaltered in spite of repeated bending 300 cycles, demonstrating good flexibility and durability of the superhydrophobic surface. This is of great significance for using the Janus paper in practical applications. A sand impact test was performed to characterize the mechanical resistance ability of the as-prepared superhydrophobic surface to physical insults.26,27 As shown in Figure 6A,

biphase system, which was composed of hexane (upper phase) and water (lower phase). First, both pristine filter paper and dyed Janus paper stayed at the hexane/water interface (Figure 4A,E). Dyed water (10 μL) spread quickly on the pristine filter

Figure 4. Pristine filter paper (A) and superwettable Janus paper (E) at the hexane/water interface initially. Dyed water droplet spread on the pristine paper (B) but formed a sphere on the Janus paper (F). If the hexane/water mixture was stirred or shaken (C,G), the pristine filter paper sank to the bottom (D), while the Janus paper remained at the hexane/water interface (H).

paper, whereas formed a spherical droplet on the superhydrophobic surface of the Janus paper (Figure 4B,F). If the biphase system was stirred, rocked, or shaken, the pristine paper penetrated the water phase and sank to the system bottom, whereas the Janus paper stuck at the interface of hexane/water. Importantly, continuous stirring or rocking the biphase system cannot flip the Janus paper over, with the superhydrophobic surface always upward. This experiment indicates the as-prepared Janus paper possesses antirocking capability arising from its Janus superwettability. The stable interfacial floatability of the Janus paper in the biphase system may provide clue to the design of high-performance micro-/ nano-sized floatation devices.25 The mechanical durability of the superhydrophobic performance relates directly to practical applications. Common physical damages in daily life may destroy the paper surface severely and compromise the superhydrophobic performance of the Janus paper. A bending test was carried out to examine the durability of the as-prepared Janus paper. Figure 5 shows the WCAs of

Figure 6. (A) Sand impact setup. (B,D) Optical microscopy images of the superhydrophobic surface before and after the sand impact test. The insets in (B,D) are WCA images of each surface. (C) SEM image of the superhydrophobic surface after the sand impact test. Yellow arrows indicate trapped sand grains. The inset in (C) shows representative damage of the superhydrophobic surface caused by sand impact.

the Janus paper under investigation was tilted by 45° and impacted by 40 g of sand particles flowed out of a steel funnel 100 cm above the substrate surface in 60 s. Figure 6B,D shows optical microscopy images (insets: WCA images) of the superhydrophobic paper before and after sand impact abrasion, respectively. As seen from Figure 6C,D, sand grains were trapped in the fiber network. Notably, the superhydrophobicity of the printed paper remained intact with a WCA of 153°, although random abrasion damages appeared after the sand impact, as shown in Figure 6C. Moreover, the superhydrophilicity of the nonprinted side of the Janus paper was also intact after sand impact (Figure S2) testifying that both sides of the Janus paper could withstand the sand abrasion test. The robustness of films/coatings to the sand impact test was found to be highly dependent on the mass of sands and the falling height. It is worth to mention that the mass of sand and the falling height in our test are higher than those reported in previous works,26,27 indicating that the as-prepared Janus surface is able to withstand more severe sand impact abrasion. Furthermore, a water washing test was carried out to evaluate the water resistance of surface coatings. A piece of Janus paper was put into a bottle filled with water and shaken for 1 h. After dried in an oven, the WCA of the inkjet-printed side of the Janus paper was measured (Figure S3). It is indicated that the superhydrophobicity of the Janus paper was intact after water washing with an average WCA of 151°. Importantly, after being stored at ambient temperature for 10 months, the superhydrophilicity−superhydrophobicity of the Janus paper remained the same as its initial status (Figure S3).

Figure 5. WCAs of the superhydrophobic surface of the Janus paper upon bending cycles at a bending radius of 7 mm. Insets are illustrations of the bending test and corresponding WCA images of the surface before bending and after 300 bending cycles. D


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Figure 7. (A,B) Predesigned patterns to be printed. (C,D) Resolution of hydrophobic barriers and hydrophilic channels. (E,F) Optical microscopy images of rectangled areas, demonstrating the borderline integrity of printed patterns. The unit of the dimension numbers below (A,B) is mm.

assay reproducibility than manual deposition but also prevent waste of the expensive reagent, thanks to small droplet volumes from the printer (∼1.5 pL). As illustrated in Figure 8, first, a

To further demonstrate the precise hydrophobization potentials of inkjet printing, superwettable microfluidic patterns were produced on the paper substrate. As demonstrated in Figures 3 and S1, the increase of the number of printing passes led to thicker hydrophobic coatings, which are beneficial for the confinement of liquid in microfluidic channels. However, the print precision is usually hampered by increasing the number of printing passes. Thus, a more sophisticated method was proposed here by printing on both sides of the paper. First, a Janus paper was produced by two inkjet printing passes, and then, the predesigned microfluidic patterns were printed onto the superhydrophilic side of the Janus paper. Thus, the superwettable microfluidic patterned paper was obtained, and the liquid to be contained will just stay in the barrier region without any bleeding through the barrier or the back side of the paper. It is worth to mention that if the patterns were inkjetprinted on the pristine paper, water droplet imbibition to the nonprinted side would occur as shown in Figure S6. Figure 7A,B demonstrates two predesigned microfluidic patterns by the SolidWorks software.28 Figure 7C,D shows two examples of printed microfluidic patterns after dyed water was dropped on the triangle region and underwent capillary driven flow along the untreated cellulose (hydrophilic) channels. Note that a 30 μL CuSO4 solution droplet formed a spherical droplet on the inkjet-printed (superhydrophobic) area. These two examples of paper-based microfluidic patterns indicated the precision and resolution of printed functional hydrophobic barriers and hydrophilic channels, respectively. The narrowest fully wetted hydrophilic channel was the fourth from the right (600 μm in width). Because of the slight diffusion of the hydrophobic modifier during inkjet printing, the gaps/channel with designed width lower than 600 μm were readily blocked by hydrophobic coating, which prevented water from wicking into channels. The narrowest hydrophobic barrier capable of blocking aqueous dye solution was the third from the right, e.g., a barrier that could prevent aqueous solutions from crossing it should be wider than 400 μm in designed width. Nickel is an essential trace element for humans because of its presence in proteins and involvement in hormone actions and metabolic processes. However, nickel overload can cause poisoning with unique symptoms of dermatitis, respiratory disorders, and respiratory cancer. Thus, a simple, rapid, and low-cost visualization method for the field detection of Ni(II) is particularly significant.29 In this work, an application of the paper-based superwettable patterns was demonstrated as PADs for Ni(II) assays. Both hydrophobic barriers and colorimetric reagents were inkjet-printed for Ni(II) analysis. Reagent deposition by inkjet printing could not only provide better

Figure 8. Fabrication process (A) and performance verification (B) of PADs for Ni(II) assays. The scale bars in (B) are 5 mm.

hollow flower-shaped superhydrophobic pattern was fabricated on a Janus paper. Followed by inkjet printing the indicator solution (DMG in ethanol) into the flower pattern, a PAD for Ni(II) analysis was obtained. The performance of the PADs under investigation were examined by applying them in water samples containing various amounts of Ni(II). As the concentration of Ni(II) increases from 0 to 5 and 10 mM, the magenta color of the flower pattern became deeper on account of the colorimetric reaction of DMG with Ni(II) (see Figure 8B). This demonstration provides new opportunities for colorimetric PADs with good sensitivity as well as interestingness.

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CONCLUSIONS In the current work, we demonstrated that inkjet printing enabled precise control of hydrophobic functionalization of papers in both planar and steric dimensions. Moreover, elaborate control of ink droplets by an inkjet printer facilitated ingenious construction of nanoscale roughness on cellulose fibers. Association of hydrophobic functionalization and hierarchical roughness endows the paper with superhydrophobicity. For the first time, the fabrication of superwettable Janus paper was presented by using inkjet printing approach. In addition, by using inkjet printing paper-based superwettable patterns were fabricated as well, which show prospective applications in microfluidics and analysis. The microscale resolution of printed microfluidics and the verification of constructed PADs for Ni(II) assays were exhibited. The whole production processes of superwettable Janus surfaces and E


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(7) Yang, H.-C.; Hou, J.; Chen, V.; Xu, Z.-K. Janus Membranes: Exploring Duality for Advanced Separation. Angew. Chem., Int. Ed. 2016, 55, 13398−13407. (8) Ren, T.; He, J. Substrate-Versatile Approach to Robust Antireflective and Superhydrophobic Coatings with Excellent SelfCleaning Property in Varied Environments. ACS Appl. Mater. Interfaces 2017, 9, 34367−34376. (9) Geng, Z.; He, J.; Xu, L.; Yao, L. Rational Design and Elaborate Construction of Surface Nano-Structures toward Highly Antireflective Superamphiphobic Coatings. J. Mater. Chem. A 2013, 1, 8721−8724. (10) Lee, S. G.; Ham, D. S.; Lee, D. Y.; Bong, H.; Cho, K. Transparent Superhydrophobic/Translucent Superamphiphobic Coatings Based on Silica−Fluoropolymer Hybrid Nanoparticles. Langmuir 2013, 29, 15051−15057. (11) Ge, D.; Yang, L.; Zhang, Y.; Rahmawan, Y.; Yang, S. Transparent and Superamphiphobic Surfaces from One-Step Spray Coating of Stringed Silica Nanoparticle/Sol Solutions. Part. Part. Syst. Charact. 2014, 31, 763−770. (12) Airoudj, A.; Gall, F. B.-L.; Roucoules, V. Textile with Durable Janus Wetting Properties Produced by Plasma Polymerization. J. Phys. Chem. C 2016, 120, 29162−29172. (13) Wang, Z.; Wang, Y.; Liu, G. Rapid and Efficient Separation of Oil from Oil-in-Water Emulsions Using a Janus Cotton Fabric. Angew. Chem., Int. Ed. 2016, 55, 1291−1294. (14) Li, J.; Rossignol, F.; Macdonald, J. Inkjet Printing for Biosensor Fabrication: Combining Chemistry and Technology for Advanced Manufacturing. Lab Chip 2015, 15, 2538−2558. (15) Cate, D. M.; Adkins, J. A.; Mettakoonpitak, J.; Henry, C. S. Recent Developments in Paper-Based Microfluidic Devices. Anal. Chem. 2015, 87, 19−41. (16) Yamada, K.; Henares, T. G.; Suzuki, K.; Citterio, D. Paper-Based Inkjet-Printed Microfluidic Analytical Devices. Angew. Chem., Int. Ed. 2015, 54, 5294−5310. (17) Choi, J. R.; Tang, R.; Wang, S.; Abas, W. A. B. W.; PingguanMurphy, B.; Xu, F. Paper-Based Sample-to-Answer Molecular Diagnostic Platform for Point-of-Care Diagnostics. Biosens. Bioelectron. 2015, 74, 427−439. (18) Carrilho, E.; Martinez, A. W.; Whitesides, G. M. Understanding Wax Printing: A Simple Micropatterning Process for Paper-Based Microfluidics. Anal. Chem. 2009, 81, 7091−7095. (19) Martinez, A. W.; Phillips, S. T.; Butte, M. J.; Whitesides, G. M. Patterned Paper as a Platform for Inexpensive, Low-Volume, portable bioassays. Angew. Chem., Int. Ed. 2007, 46, 1318−1320. (20) Li, C.; Boban, M.; Snyder, S. A.; Kobaku, S. P. R.; Kwon, G.; Mehta, G.; Tuteja, A. Paper-Based Surfaces with Extreme Wettabilities for Novel, Open-Channel Microfluidic Devices. Adv. Funct. Mater. 2016, 26, 6121−6131. (21) Balu, B.; Berry, A. D.; Patel, K. T.; Breedveld, V.; Hess, D. W. Directional Mobility and Adhesion of Water Drops on Patterned Superhydrophobic Surfaces. J. Adhes. Sci. Technol. 2011, 25, 627−642. (22) Zhang, Y.; Li, T.; Ren, T.; Fang, D.; He, J. Hydrophobic/ Lipophobic Barrier Capable of Confining Aggressive Liquids for Paper-Based Assay. Colloids Surf., A 2017, 520, 544−549. (23) Cassie, A. B. D.; Baxter, S. Wettability of Porous Surfaces. Trans. Faraday Soc. 1944, 40, 546−551. (24) Wenzel, R. N. Resistance of Solid Surfaces to Wetting by Water. Ind. Eng. Chem. 1936, 28, 988−994. (25) Zhao, Y.; Yu, C.; Lan, H.; Cao, M.; Jiang, L. Improved Interfacial Floatability of Superhydrophobic/Superhydrophilic Janus Sheet Inspired by Lotus Leaf. Adv. Funct. Mater. 2017, 27, 1701466. (26) Xu, L.; Geng, Z.; He, J.; Zhou, G. Mechanically Robust, Thermally Stable, Broadband Antireflective, and Superhydrophobic Thin Films on Glass Substrates. ACS Appl. Mater. Interfaces 2014, 6, 9029−9035. (27) Jiang, L.; Tang, Z.; Clinton, R. M.; Breedveld, V.; Hess, D. W. Two-Step Process to Create “Roll-Off” Superamphiphobic Paper Surfaces. ACS Appl. Mater. Interfaces 2017, 9, 9195−9203.

patterns include mainly hydrophobic colloid preparation and printing steps, demonstrating mass production potentials of inkjet printing. We believe that this research would open new possibilities toward the construction of functional surfaces/ patterns, especially binary cooperative systems and bring broad applications in oil/water separation, surfboard/ship coating, functional textile, and biochemical analysis.

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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/acsami.8b01133. SEM cross-sectional views of pristine and inkjet-printed paper and thicknesses of each sample based on three measurements; water contact angle of the hydrophilic side of the Janus paper after the sand abrasion test; water contact angles of the inkjet-printed side of the Janus paper after 10 months storage and washing test; water droplet state on the superhydrophobic surface of Janus paper tilted at 40°; AFM images of inkjet-printed surfaces; and hydrophobic barriers and hydrophilic channels inkjet-printed on the pristine paper substrate. (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: +86 10 82543535. ORCID

Junhui He: 0000-0002-3309-9049 Author Contributions §

Y.Z. and T.R. contributed equally to this work.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was financially supported by the National Key Research and Development Program of China (2017YFA0207102), the Innovative Talents Cultivation Project of Technical Institute of Physics and Chemistry, the Chinese Academy of Sciences (2014-Z), the National Natural Science Foundation of China (grant no. 21571182), and the Science and Technology Commission of Beijing Municipality (Z151100003315018).

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REFERENCES

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Inkjet Printing Enabled Controllable Paper Superhydrophobization

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