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Fabrication and application of novel hydrophilic nanomold
ARTICLE IN PRESS
Journal of Physics and Chemistry of Solids 69 (2008) 1436–1438 www.elsevier.com/locate/jpcs
Fabrication and application of novel hydrophilic nanomold Lan-Young Hong, Dong-Hoon Lee, Dong-Pyo Kim School of Applied Chemistry and Biological Engineering, Chungnam National University, 220 Kung-Dong, Yoseong Gu, Daejeon 305-764, Republic of Korea Received 2 July 2007; received in revised form 28 September 2007; accepted 30 October 2007
Abstract We fabricated novel hydrophilic micro/nanostructures on Si substrates using a patented hydrophilic hybrid polymer with excellent processability by soft lithography methods such as the imprinting lithographic technique and microtransfer molding (mTM). Nanoscaled hydrophilic polymer patterns were fabricated with economic nanoscale compact disc (CD), DVD, and blue ray disc (BD) masters using imprint lithography. Novel hydrophilic micro/nanostructures were fabricated on Si substrates using the hydrophilic hybrid polymer with excellent processability by soft lithography methods, such as the imprinting lithographic technique and mTM even on the sub-micron level. Also, hydrophilic material was fabricated from the BD master by means of a nanoscale mold. The PDMS mold was not possible to reproduce due to high viscosity, but the hydrophilic material pattern was reproduced accurately because of its low viscosity and low surface tension. So we successfully could fabricate micro/nanoinorganic replica structures using novel hydrophilic molds. Moreover, three-dimensional microstructures with hydrophilic properties are of interest for their possible use in areas such as optics, for example photonic band-gap structures, and tissue engineering. r 2007 Elsevier Ltd. All rights reserved. Keywords: A. Inorganic compounds; A. Nanostructures; D. Microstructure; D. Surface properties
1. Introduction Coating materials designed to exhibit extreme wetting characteristics such as superhydrophilicity and superhydrophobicity have the potential to open up entirely new avenues for manipulating and controlling the interaction of surfaces. Self-cleaning, antifogging, and bacterial-resistant surfaces are but a few examples of some of the applications that could be developed through the creation of surfaces that either resist wetting or are completely wetted by water [1]. Titanium dioxide has found applications in various fields, such as self-cleaning materials, the purification of polluted water and air, antisepsis pottery and anti-fogging glass [2]. Moreover, the sol–gel process is a chemical technology, which can be very well employed to prepare inorganic as well as organically modified inorganic materials via the hydrolysis and condensation of metal
Corresponding author. Tel.: +82 42 821 6695; fax: +82 42 823 6665.
E-mail address: [email protected] (D.-P. Kim). 0022-3697/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2007.10.108
alkoxides [3,4]. Various hydrophilic materials such as coatings, fibers, and composites have been fabricated by applying the forming process to viscous polymeric precursors. Despite the development of various techniques to fabricate nanoscale patterns, there have been no reports on the fabrication of hydrophilic material patterns at the submicron scale. This paper compared two techniques for fabricating micro- and nanoscale hydrophilic material patterns and structures on Si substrates by utilizing soft lithography with a low viscous hybrid polymeric precursor, viz. the imprinting lithographic technique. In addition, compact discs (CDs), DVDs, and blue ray discs (BDs) were used as available nanoscale test masters, in order to avoid the use of expensive nanoscale masters. It is believed that this work represents an important milestone in the utilization of hydrophilic materials in areas such as nanocomponents or devices. In particular, the micropatterning of hydrophilic polymers can be used to study cell behavior on controlled surfaces, to fabricate lipid-assisted biochips such as DNA-chips, and to study lipid activity kinetics [5,6].
ARTICLE IN PRESS L.-Y. Hong et al. / Journal of Physics and Chemistry of Solids 69 (2008) 1436–1438
2. Experimental method SiO2–TiO2 composite sols of the patented hydrophilic polymer were prepared by mixing the suitable ratios of silica sols and titania sols, which tetraethylorthosilicate (TEOS) and TiCl4 were hydrolyzed in ethanol–water containing HCl. Nonionic triblock copolymer, Pluronic P123 (EO20PO70EO20) was added in SiO2–TiO2 sols, which was used as a structure-directing agent. For the preparation of organic/inorganic hybrid coating solution, the SiO2–TiO2 composite sols were mixed with the desired amount of 3-methacryloxypropyltrimethoxysilane as a silane coupling agent and polyethylene glycol dimethacrylate as a hydrophilic organic component, respectively [7].
Substrate
SSpin-coat polymer
Polymer
P Place a PDMS mold
PDMS
Curing/removal of PDMS mold
Fig. 1. A schematic diagram of imprint lithography method.
1437
For mono-layer patterns using imprint lithography technique, CD and BD were used as nanoscale test masters to fabricate mono-layer nanoscale patterns. The low viscous hydrophilic polymer precursor was spin coated on the BD master at a spin rate of 1000 rpm for 20 s. The PDMS pattern from a CD master was used to fabricate the hydrophilic polymer pattern via imprint lithography, while the PDMS mold from a BD master is difficult to reproduce exactly by imprint lithography. Therefore, BD patterns were directly made from BD master using hydrophilic material, without using the PDMS mold. Fig. 1 shows the schemes used for the imprint lithographic technique. The wetting behavior of the coating was examined by measuring the contact angle of the coated and uncoated glass slide in contact angle goniometry (PSA100, KRUSS GmbH). The coating morphology of the coated film on a glass slide was determined by scanning electron microscope (SEM; PHILIPS, XL30SFEG) and noncontact AFM mode (PSIA, WE-100).
3. Results and discussion The PDMS mold has been widely used in imprint lithography due to many advantages. But the adhesion between the PDMS mold and the patterned materials is often problematic at demolding stage. Therefore, it is expected that novel hydrophilic polymer can be an excellent patterning material with less adhesion to the hydrophobic PDMS mold, and the removal of the PDMS mold may be easier with no stiction problem in imprint lithography method. Fig. 2 shows the AFM images of the CD master, PDMS mold and cured hydrophilic material pattern formed by the imprint lithography. Compared with the original features on the CD master (1.0 mm; width, 200 nm; depth) (Fig. 2a), the PDMS was well transferred (1.0 mm; width, 200 nm; depth) in Fig. 2b, and the hydrophilic material was patterned with a 1 mm (width) and 120 nm (depth) (Fig. 2c) without any distortion or defects in a single step. The height of the cured polymer pattern was lower than that of the master or the PDMS mold, which was attributed to the low wettability of the hydrophilic polymer and the lack of forced infiltration with pressure into the mold. However, the contact angle of
Fig. 2. The AFM images of (a) CD master, (b) PDMS mold, (c) patterned hydrophilic material from PDMS mold, and (d) SEM image of the hydrophilic material pattern.
ARTICLE IN PRESS 1438
L.-Y. Hong et al. / Journal of Physics and Chemistry of Solids 69 (2008) 1436–1438
Fig. 3. Modified imprint lithography result from BD master: (a) AFM image for BD master, (b) AFM image for cured pattern, and (c) SEM image for pattern of the hydrophilic material polymer.
Fig. 4. The SEM images of 3D microstructures of hydrophilic material fabricated using mTM.
cured pattern is more increased at ca. 551 than the contact angle of the thin film (ca. 101). It is proven that the increased surface roughness modified the surface wettability. Alternatively, the finer nanoscale patterns were also fabricated by modified imprint lithography with no use of PDMS mold. Fig. 3 shows SEM and AFM images of the BD master and cured polymer pattern. In the nanopatterns from BD master (363 nm; pitch, 23 nm; depth) (Fig. 3a), the hydrophilic patterns were well transferred with a respective pitch (363 nm) and depth (23 nm) (Fig. 3b). At this work, microtransfer molding (mTM) technique was used to generate both isolated and interconnected microstructures without spin-coating process unlike imprint lithography. Double-layer hydrophilic structures were fabricated by mTM as shown in Fig. 4. Even when fabricated with care, the edges of lines shown in Fig. 4 were still a little softened and blurred. Furthermore, the double layer structures at nanoscale are more challenging to fabricate, which is currently understudy. PDMS mold was not possible to reproduce at nanoscale patterns due to the high viscosity, but hydrophilic material pattern was reproduced accurately because of its low viscosity and low surface tension. The nanoscaled hydrophilic patterns can be used at novel mold materials instead of PDMS mold. And three-dimensional
microstructures with hydrophillic property are interesting for possible use in areas such as optics, for example, photonic band-gap structure, and tissue engineering. Acknowledgments This work was supported by the Center for Nanoscale Mechatronics & Manufacturing Project [M 102KN01000706K1401-00712]. References [1] F.C. Cebeci, Z. Wu, L. Zhai, R.E. Cohen, M.F. Ruber, Langmuir 22 (2006) 2856. [2] D. Ren, X. Cui, J. Shen, Q. Zhang, X. Yang, Z. Zhang, L. Ming, J. Sol–gel Sci. Technol. 29 (2004) 131. [3] S. Hofacker, M. Mechtel, M. Mager, H. Kraus, Prog. Org. Coatings 45 (2002) 159. [4] J.D. Jentsch, M. Mager, M. Mechtel, US 6005131, 1999, Bayer AG. [5] G.M. Bruisma, H.C. van Der Mei, H.J. Busscher, Biomaterials 22 (2001) 3217. [6] M. Metzke, J.Z. Bai, Z. Guan, J. Am. Chem. Soc. 125 (2003) 7760. [7] D.P. Kim, L.Y. Hong, J.H. Won, Y.S. Park, C.K. Shin, WO 2007069867 A1.
Journal of Physics and Chemistry of Solids 69 (2008) 1436–1438 www.elsevier.com/locate/jpcs
Fabrication and application of novel hydrophilic nanomold Lan-Young Hong, Dong-Hoon Lee, Dong-Pyo Kim School of Applied Chemistry and Biological Engineering, Chungnam National University, 220 Kung-Dong, Yoseong Gu, Daejeon 305-764, Republic of Korea Received 2 July 2007; received in revised form 28 September 2007; accepted 30 October 2007
Abstract We fabricated novel hydrophilic micro/nanostructures on Si substrates using a patented hydrophilic hybrid polymer with excellent processability by soft lithography methods such as the imprinting lithographic technique and microtransfer molding (mTM). Nanoscaled hydrophilic polymer patterns were fabricated with economic nanoscale compact disc (CD), DVD, and blue ray disc (BD) masters using imprint lithography. Novel hydrophilic micro/nanostructures were fabricated on Si substrates using the hydrophilic hybrid polymer with excellent processability by soft lithography methods, such as the imprinting lithographic technique and mTM even on the sub-micron level. Also, hydrophilic material was fabricated from the BD master by means of a nanoscale mold. The PDMS mold was not possible to reproduce due to high viscosity, but the hydrophilic material pattern was reproduced accurately because of its low viscosity and low surface tension. So we successfully could fabricate micro/nanoinorganic replica structures using novel hydrophilic molds. Moreover, three-dimensional microstructures with hydrophilic properties are of interest for their possible use in areas such as optics, for example photonic band-gap structures, and tissue engineering. r 2007 Elsevier Ltd. All rights reserved. Keywords: A. Inorganic compounds; A. Nanostructures; D. Microstructure; D. Surface properties
1. Introduction Coating materials designed to exhibit extreme wetting characteristics such as superhydrophilicity and superhydrophobicity have the potential to open up entirely new avenues for manipulating and controlling the interaction of surfaces. Self-cleaning, antifogging, and bacterial-resistant surfaces are but a few examples of some of the applications that could be developed through the creation of surfaces that either resist wetting or are completely wetted by water [1]. Titanium dioxide has found applications in various fields, such as self-cleaning materials, the purification of polluted water and air, antisepsis pottery and anti-fogging glass [2]. Moreover, the sol–gel process is a chemical technology, which can be very well employed to prepare inorganic as well as organically modified inorganic materials via the hydrolysis and condensation of metal
Corresponding author. Tel.: +82 42 821 6695; fax: +82 42 823 6665.
E-mail address: [email protected] (D.-P. Kim). 0022-3697/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2007.10.108
alkoxides [3,4]. Various hydrophilic materials such as coatings, fibers, and composites have been fabricated by applying the forming process to viscous polymeric precursors. Despite the development of various techniques to fabricate nanoscale patterns, there have been no reports on the fabrication of hydrophilic material patterns at the submicron scale. This paper compared two techniques for fabricating micro- and nanoscale hydrophilic material patterns and structures on Si substrates by utilizing soft lithography with a low viscous hybrid polymeric precursor, viz. the imprinting lithographic technique. In addition, compact discs (CDs), DVDs, and blue ray discs (BDs) were used as available nanoscale test masters, in order to avoid the use of expensive nanoscale masters. It is believed that this work represents an important milestone in the utilization of hydrophilic materials in areas such as nanocomponents or devices. In particular, the micropatterning of hydrophilic polymers can be used to study cell behavior on controlled surfaces, to fabricate lipid-assisted biochips such as DNA-chips, and to study lipid activity kinetics [5,6].
ARTICLE IN PRESS L.-Y. Hong et al. / Journal of Physics and Chemistry of Solids 69 (2008) 1436–1438
2. Experimental method SiO2–TiO2 composite sols of the patented hydrophilic polymer were prepared by mixing the suitable ratios of silica sols and titania sols, which tetraethylorthosilicate (TEOS) and TiCl4 were hydrolyzed in ethanol–water containing HCl. Nonionic triblock copolymer, Pluronic P123 (EO20PO70EO20) was added in SiO2–TiO2 sols, which was used as a structure-directing agent. For the preparation of organic/inorganic hybrid coating solution, the SiO2–TiO2 composite sols were mixed with the desired amount of 3-methacryloxypropyltrimethoxysilane as a silane coupling agent and polyethylene glycol dimethacrylate as a hydrophilic organic component, respectively [7].
Substrate
SSpin-coat polymer
Polymer
P Place a PDMS mold
PDMS
Curing/removal of PDMS mold
Fig. 1. A schematic diagram of imprint lithography method.
1437
For mono-layer patterns using imprint lithography technique, CD and BD were used as nanoscale test masters to fabricate mono-layer nanoscale patterns. The low viscous hydrophilic polymer precursor was spin coated on the BD master at a spin rate of 1000 rpm for 20 s. The PDMS pattern from a CD master was used to fabricate the hydrophilic polymer pattern via imprint lithography, while the PDMS mold from a BD master is difficult to reproduce exactly by imprint lithography. Therefore, BD patterns were directly made from BD master using hydrophilic material, without using the PDMS mold. Fig. 1 shows the schemes used for the imprint lithographic technique. The wetting behavior of the coating was examined by measuring the contact angle of the coated and uncoated glass slide in contact angle goniometry (PSA100, KRUSS GmbH). The coating morphology of the coated film on a glass slide was determined by scanning electron microscope (SEM; PHILIPS, XL30SFEG) and noncontact AFM mode (PSIA, WE-100).
3. Results and discussion The PDMS mold has been widely used in imprint lithography due to many advantages. But the adhesion between the PDMS mold and the patterned materials is often problematic at demolding stage. Therefore, it is expected that novel hydrophilic polymer can be an excellent patterning material with less adhesion to the hydrophobic PDMS mold, and the removal of the PDMS mold may be easier with no stiction problem in imprint lithography method. Fig. 2 shows the AFM images of the CD master, PDMS mold and cured hydrophilic material pattern formed by the imprint lithography. Compared with the original features on the CD master (1.0 mm; width, 200 nm; depth) (Fig. 2a), the PDMS was well transferred (1.0 mm; width, 200 nm; depth) in Fig. 2b, and the hydrophilic material was patterned with a 1 mm (width) and 120 nm (depth) (Fig. 2c) without any distortion or defects in a single step. The height of the cured polymer pattern was lower than that of the master or the PDMS mold, which was attributed to the low wettability of the hydrophilic polymer and the lack of forced infiltration with pressure into the mold. However, the contact angle of
Fig. 2. The AFM images of (a) CD master, (b) PDMS mold, (c) patterned hydrophilic material from PDMS mold, and (d) SEM image of the hydrophilic material pattern.
ARTICLE IN PRESS 1438
L.-Y. Hong et al. / Journal of Physics and Chemistry of Solids 69 (2008) 1436–1438
Fig. 3. Modified imprint lithography result from BD master: (a) AFM image for BD master, (b) AFM image for cured pattern, and (c) SEM image for pattern of the hydrophilic material polymer.
Fig. 4. The SEM images of 3D microstructures of hydrophilic material fabricated using mTM.
cured pattern is more increased at ca. 551 than the contact angle of the thin film (ca. 101). It is proven that the increased surface roughness modified the surface wettability. Alternatively, the finer nanoscale patterns were also fabricated by modified imprint lithography with no use of PDMS mold. Fig. 3 shows SEM and AFM images of the BD master and cured polymer pattern. In the nanopatterns from BD master (363 nm; pitch, 23 nm; depth) (Fig. 3a), the hydrophilic patterns were well transferred with a respective pitch (363 nm) and depth (23 nm) (Fig. 3b). At this work, microtransfer molding (mTM) technique was used to generate both isolated and interconnected microstructures without spin-coating process unlike imprint lithography. Double-layer hydrophilic structures were fabricated by mTM as shown in Fig. 4. Even when fabricated with care, the edges of lines shown in Fig. 4 were still a little softened and blurred. Furthermore, the double layer structures at nanoscale are more challenging to fabricate, which is currently understudy. PDMS mold was not possible to reproduce at nanoscale patterns due to the high viscosity, but hydrophilic material pattern was reproduced accurately because of its low viscosity and low surface tension. The nanoscaled hydrophilic patterns can be used at novel mold materials instead of PDMS mold. And three-dimensional
microstructures with hydrophillic property are interesting for possible use in areas such as optics, for example, photonic band-gap structure, and tissue engineering. Acknowledgments This work was supported by the Center for Nanoscale Mechatronics & Manufacturing Project [M 102KN01000706K1401-00712]. References [1] F.C. Cebeci, Z. Wu, L. Zhai, R.E. Cohen, M.F. Ruber, Langmuir 22 (2006) 2856. [2] D. Ren, X. Cui, J. Shen, Q. Zhang, X. Yang, Z. Zhang, L. Ming, J. Sol–gel Sci. Technol. 29 (2004) 131. [3] S. Hofacker, M. Mechtel, M. Mager, H. Kraus, Prog. Org. Coatings 45 (2002) 159. [4] J.D. Jentsch, M. Mager, M. Mechtel, US 6005131, 1999, Bayer AG. [5] G.M. Bruisma, H.C. van Der Mei, H.J. Busscher, Biomaterials 22 (2001) 3217. [6] M. Metzke, J.Z. Bai, Z. Guan, J. Am. Chem. Soc. 125 (2003) 7760. [7] D.P. Kim, L.Y. Hong, J.H. Won, Y.S. Park, C.K. Shin, WO 2007069867 A1.