pubs.acs.org/Langmuir © 2010 American Chemical Society
Rewritable Superhydrophilic-Superhydrophobic Patterns on a Sintered Titanium Dioxide Substrate Kazuya Nakata,† Shunsuke Nishimoto,† Yumi Yuda,† Tsuyoshi Ochiai,† Taketoshi Murakami,† and Akira Fujishima*,†,‡ †
Photocatalyst group, Kanagawa Academy of Science and Technology, KSP West 614, 3-2-1 Sakado, Takatsu-ku, Kawasaki, Kanagawa 213-0012, Japan, and ‡Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan Received May 15, 2010. Revised Manuscript Received June 10, 2010
This Letter describes a new fabrication process for superhydrophilic-superhydrophobic patterns on a TiO2 surface using a combination of an inkjet technique and the site-selective decomposition of a self-assembled monolayer (SAM) by a photocatalytic reaction under UV irradiation. To induce high surface wettability, we carried out simple calcination of a Ti substrate. The substrate was thus oxidized to titanium oxide and had a vortex-like rough morphology, which was suitable for the formation of wettability patterns. Furthermore, the substrate can be regenerated after elimination of the superhydrophilic-superhydrophobic patterns by the photocatalytic decomposition of TiO2 using UV irradiation, and the patterns are deposited again. The renewed surface that we created had a wettability pattern that was different from the preceding pattern. This process is based on a TiO2 surface and should offer a renewable, resource-saving, and environmentally friendly methodology for the formation of wettability patterns.
Introduction Wettability patterns have been applied to many fundamental and industrial applications such as fluidic devices,1 spotting of cells2 and DNA,3 and offset printing.4 Titanium dioxide (TiO2) is used in the fabrication of wettability patterns, as it allows a superhydrophilic state and it decomposes organic chemicals under UV irradiation.5 The combination of these two properties enables the fabrication of wettability patterns with organic selfassembled monolayers (SAMs).6 The high resolution wettability patterns need to have superhydrophilic and superhydrophobic surfaces, which have previously been fabricated on rough surfaces.7 However, only a few reports have dealt with the preparation of TiO2-based superhydrophilic-superhydrophobic patterns.
This is due to the lack of convenient preparation methods for rough surfaces, as currently multiple processes7,8 or surface etching using hazardous chemicals are used.6 We thus report the fabrication of superhydrophilicsuperhydrophobic patterns on a TiO2 surface modified with SAMs and subsequent selective UV irradiation using water-based ink from an inkjet printer. To increase the surface wettability, we roughened the surface using a simple and reproducible method where titanium foil is calcined at high temperature in air. We further demonstrate that the wettability patterns on the TiO2 surface can be erased by UV irradiation over the whole surface and subsequent resurfacing enables us to produce repeated superhydrophobic-superhydrophilic patterns.
Experimental Section *To whom correspondence should be addressed. Phone: þ81-3-3260-4271. Fax: þ81-3-3260-4370. E-mail:
[email protected].
(1) (a) Gau, H.; Herminghaus, S.; Lenz, P.; Lipowsky, R. Science 1999, 283 (5398), 46. (b) Handique, K.; Burke, D. T.; Mastrangelo, C. H.; Burns, M. A. Anal. Chem. 2000, 72, 4100. (2) (a) Ito, Y. Biomaterials 1999, 20(23-24), 2333. (b) Lopez, G. P.; Albers, M. W.; Schreiber, S. L.; Carroll, R.; Peralta, E.; Whitesides, G. M. J. Am. Chem. Soc. 1993, 115(13), 5877. (3) Gillmor, S. D.; Thiel, A. J.; Strother, T. C.; Smith, L. M.; Lagally, M. G. Langmuir 2000, 16(18), 7223. (4) (a) Nakata, K.; Nishimoto, S.; Kubo, A.; Tryk, D. A.; Ochiai, T.; Murakami, T.; Fujishima, A. Chem.;Asian J. 2009, 4, 988. (b) Nishimoto, S.; Kubo, A.; Nohara, K.; Zhang, X.; Taneichi, N.; Okui, T.; Liu, Z.; Nakata, K.; Sakai, H.; Murakami, T.; Abe, M.; Komine, T.; Fujishima, A. Appl. Surf. Sci. 2009, 255(12), 6221. (5) (a) Wang, R.; Hashimoto, K.; Fujishima, A.; Chikuni, M.; Kojima, E.; Kitamura, A.; Shimohigoshi, M.; Watanabe, T. Nature 1997, 388(6641), 431. (b) Fujishima, A.; Rao, T. N.; Tryk, D. A. J. Photochem. Photobiol., C 2000, 1, 1. (c) Fujishima, A.; Zhang, X.; Tryk, D. A. Surf. Sci. Rep. 2008, 63, 515. (d) Fujishima, A.; Hashimoto, K.; Watanabe, T.,TiO2 Photocatalysis: Fundamentals and Applications; BKC: Tokyo, 1999.(e) Noguchi, T.; Fujishima, A. Environ. Sci. Technol. 1998, 32(23), 3831. (f) Fujishima, A.; Rao, T. N.; Tryk, D. A. Electrochim. Acta 2000, 45(28), 4683. (6) (a) Zhang, X.; Jin, M.; Liu, Z.; Nishimoto, S.; Saito, H.; Murakami, T.; Fujishima, A. Langmuir 2006, 22(23), 9477. (b) Zhang, X.; Jin, M.; Liu, Z.; Tryk, D. A.; Nishimoto, S.; Murakami, T.; Fujishima, A. J. Phys. Chem. C 2007, 111(39), 14521. (7) (a) Nishimoto, S.; Sekine, H.; Zhang, X.; Liu, Z.; Nakata, K.; Murakami, T.; Koide, Y.; Fujishima, A. Langmuir 2009, 25(13), 7226. (b) Tadanaga, K.; Morinaga, J.; Matsuda, A.; Minami, T. Chem. Mater. 2000, 12, 590.
11628 DOI: 10.1021/la101947y
Materials. Titanium plates (10 cm 10 cm 0.3 mm) were purchased from Nilaco. Octadecyltrimethoxysilane (ODS) was obtained from Tokyo Kasei and used without further purification. A commercially available HP Photosmart D5360 inkjet printer was used to deposit patterns with the use of a water-based ink prepared from a mixed solvent of H2O (60 mL) and 2-propanol (38 mL) containing direct blue 86 (1 g, TCI). Preparation of Superhydrophobic-Superhydrophilic Patterns.
A titanium plate was calcined at 1000 °C for 1 h in air and then cooled to room temperature. A white layer was formed on the titanium plate and spontaneously separated from the substrate while cooling. The remaining substrate was then treated with ODS by chemical vapor deposition at 120 °C for 3 h. Water-based ink patterns were deposited using an inkjet printer followed by UV-C (2 mW/cm2, 254 nm) irradiation for 2.5 h. After the surface was washed with water, superhydrophobic-superhydrophilic patterns were obtained. (8) (a) Lim, H. S.; Han, J. T.; Kwak, D.; Jin, M.; Cho, K. J. Am. Chem. Soc. 2006, 128, 14458. (b) Zhang, X.; Kono, H.; Liu, Z.; Nishimoto, S.; Tryk, D. A.; Murakami, T.; Sakai, H.; Abe, M.; Fujishima, A. Chem. Commun. 2007, 4949. (c) Feng, X.; Zhai, J.; Jiang, L. Angew. Chem., Int. Ed. 2005, 44, 5115. (d) Laia, Y.; Lina, C.; Wang, H.; Huang, J.; Zhuang, H.; Sun, L. Electrochem. Commun. 2008, 10(3), 387. (e) Borras, A.; Barranco, A.; Gonzalez-Elipe, A. R. Langmuir 2008, 24, 8021.
Published on Web 06/16/2010
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Figure 3. (a) SEM image of the surface of the remaining substrate, (b) magnified image of the vortex-like morphology, and (c) FE-SEM image of the particles on the substrate.
Figure 1. Schematic representation of the wettability pattern fabrication procedure.
Figure 2. Photographs of the delamination of the white layer from the remaining substrate after sintering at 1000 °C.
Renewal of the Substrate. The surface was illuminated using UV-C (2 mW/cm2, 254 nm) for 2.5 h. The superhydrophobicsuperhydrophilic pattern fabrication process was repeated as described for the first process.
Results and Discussion To clarify the fabrication process, all the steps in the fabrication procedure are schematically represented in Figure 1. In the first step, a titanium substrate is calcined at 1000 °C in a furnace under an air atmosphere (step 1). After 1 h, the substrate is taken out of the furnace and cooled to room temperature. Interestingly, a fragile white layer is generated and can be separated from the substrate after cooling (step 2, Figure 2). The surface of the remaining substrate consists of a TiO2 rutile phase and Ti2O as evidenced by its X-ray diffraction pattern. The delaminated white layer consists of a TiO2 rutile phase (Figure S1 in the Supporting Information). We assume that during calcination the top of the surface was oxidized to TiO2 whereas the interface between the remaining substrate and the delaminated layer was gradually oxidized, which may have generated TiO2 and the partially oxidized Ti2O. The surface of the remaining substrate was observed by scanning electron microscopy (SEM) as shown in Figure 3. A rough surface with vortex-like morphology was present, and its surface consists of small particles with an average diameter of 120 nm, which can be attributed to rutile TiO2. The surface of the delaminated layer that was attached to the remaining substrate was quite similar to the remaining substrate with regard to morphology, whereas the opposite side of the delaminated layer has a different morphology composed of crystals (Figure S2 in the Supporting Information). This method to produce the rough surface is quite simple and reproducible compared with previous works which need multiple processes7,8 or hazardous chemicals.6 Langmuir 2010, 26(14), 11628–11630
Figure 4. (a) Photographs of the water-based ink patterns and (b) the wettability patterns after the deposition of water in the first process. (c) Photographs of the water-based ink patterns and (d) the wettability patterns after the deposition of water in the secondary process. Scale bar is 5 mm.
The remaining surface was modified with a SAM of ODS to create a superhydrophobic surface with a contact angle of 160° (step 3). Water-based ink patterns were then deposited onto the surface using a conventional inkjet printer as shown in Figure 4a (step 4). Text patterns consisting of the water-based ink formed successfully on the substrate. The surface was irradiated with UV light (254 nm) for 2.5 h. The SAM of the area that was not protected by the water-based ink was photocatalytically decomposed (step 5). The water contact angles of the areas covered by the water-based ink remained superhydrophobic with a contact angle of 160° even after UV irradiation for 2.5 h, whereas the contact angles for the areas not covered with the water-based ink decreased and reached 0° after 2.5 h under UV irradiation (Figure S3 in the Supporting Information). This suggests that the water-based ink functions as a UVresistant film. The UV absorption properties can be determined by the UV/vis spectrum of the water-based ink, which has a strong absorption at 254 nm attributed to the copper phthalocyanine derivative, which is used as a dye in the water-based ink.4a To check the formation of the wettability patterns based on their superhydrophilicity-superhydrophobicity, we carried out a water deposition test. Initially, the surface containing the waterbased ink patterns was irradiated with UV light and washed with water (step 6). The surface was then dried and water deposition was carried out again. As is clearly shown in Figure 4b, the water selectively adhered to the superhydrophilic area whereas water was repelled from the superhydrophobic area where the waterbased ink patterns were present, which means that wettability patterns were successfully formed. Finally, we demonstrate the wettability pattern resurfacing process for the remaining substrate. The surface was irradiated with UV light for 2.5 h to clean the surface by removing the superhydrophilicsuperhydrophobic patterns (step 7). This process allows for the DOI: 10.1021/la101947y
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photocatalytic decomposition of the SAM over the whole surface. The surface was then reconstructed with superhydrophilicsuperhydrophobic patterns according to the previously described processes. Water-based ink text patterns that were different from those of the first process were clearly deposited as shown in Figure 4c. The surface was irradiated with UV light again and washed with water. Water was then deposited onto the substrate to check for the formation of the wettability patterns prepared by a secondary process as shown in Figure 4d. Text patterns corresponding to the water-based ink patterns were formed on the substrate. It should be noted that the wettability patterns that were prepared in first process did not appear. These results demonstrate that the prepared substrate can function as a rewritable substrate using wettability patterns.
Conclusion In conclusion, we fabricated superhydrophilic-superhydrophobic patterns by the inkjet technique and a site-selective photocatalytic
11630 DOI: 10.1021/la101947y
reaction on a rough surface. This was based on a titanium dioxide substrate prepared by the simple calcination of titanium foil which affords high wettability contrast. We have thus demonstrated that substrates containing wettability patterns are rewritable after UV irradiation, which photocatalytically removes the patterns. This methodology offers a new, resource-saving, environmentally friendly method to fabricate substrates with high contrast wettability patterns. Acknowledgment. This work was supported by a Grant-inAid for challenging Exploratory Research (No. 21654043) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. Supporting Information Available: XRD spectra, SEM images, and contact angles. This material is available free of charge via the Internet at http://pubs.acs.org.
Langmuir 2010, 26(14), 11628–11630
