Article Journal of Chemical and Biological Interfaces Vol. 1, 53 57, 2013

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1 Copyright 2013 American Scientific Publishers All rights reserved Printed in the United States of America Article Journal of Chemical and Biological Interfaces Vol. 1, 53 57, Selective Immobilization of Silver Nanoparticles onto Poly(acrylic acid)-patterned Poly(tetrafluoroethylene) Surface Prepared by Using Radiation-Induced Graft Polymerization Chan-Hee Jung 1, In-Tae Hwang 1, In-Seol Kuk 1, Oh-Sun Kwon 2, Kwanwoo Shin 2 1 3, and Jae-Hak Choi 1 Advanced Radiation Technology Institute, Korea Atomic Energy Research Institute, Jeongeup-si, Jeollabuk-do , Republic of Korea 2 Department of Chemistry and Institute of Biological Interfaces, Sogang University, Seoul , Republic of Korea 3 Department of Polymer Science and Engineering, Chungnam National University, Yusong-gu, Daejeon , Republic of Korea Selective immobilization of silver nanoparticles IP: on a On: polymer Sun, surface 08 Apr by2018 using06:47:33 ion irradiation-induced graft polymerization was demonstrated in this research. Poly(tetrafluoroethylene) Copyright: American Scientific (PTFE) films Publishers were irradiated with accelerated proton ions through a pattern mask. Acrylic acid (AA) was graft Delivered polymerized by Ingenta selectively on the irradiated regions of the PTFE surface at various fluences. The grafting degree of AA on the PTFE surface was dependant on the ion fluence and peroxide concentration. The analytical results for the chemical structure and wettability of the grafted PTFE verified the occurrence of the graft polymerization on the irradiated surface. The UV-Vis and SEM-EDX analysis revealed that silver nanoparticles were successfully immobilized on the grafted regions of the PTFE surface, and therefore, resulting in well-defined patterns of silver nanoparticles on the PTFE surface. KEYWORDS: Silver Nanoparticles, Pattern, Poly(tetrafluoroethylene), Poly(acrylic acid), Radiation-grafting, Ion Irradiation. INTRODUCTION Owing to the size-dependant properties of the metal nanoparticles, 1 3 the fabrication of patterned metal nanoparticles has received tremendous attention for a variety of applications in biochemical, electronic, photonic, and magnetic devices. 4 6 Thus, numerous research activities on patterning of metal nanoparticles by using various techniques have been carried out on inorganic substrates such as the glass, silicon, indium-tin oxide glass, and metal. 1 Recently, patterning of metal nanoparticles on a polymer substrate has been of great interest since a polymer substrate is lightweight, flexible and lower cost. 7 9 Author to whom correspondence should be addressed. s: jaehakchoi@kaeri.re.kr, jaehakchoi@cnu.ac.kr Received: 21 March 2013 Accepted: 29 March 2013 Various approaches including photolithography, surfacetemplate deposition, ink-jet printing, laser or e-beam writing, and soft lithography have been reported to pattern metal nanoparticles on a polymer substrate However, immobilization of metal nanoparticles on a polymer surface by using ion beam-induced graft polymerization has been rarely studied so far. Polytetrafluoroethylene (PTFE) is an interesting material for the applications such as a flexible printed circuit, polymer electrolyte membrane, and biomaterials because it exhibits the superior chemical resistance, low dielectric constant, good thermal stability, high mechanical strength, and biological inertness in the human body In addition, PTFE can be easily functionalized by radiationinduced grafting Therefore, PTFE was chosen as a substrate for patterning metal nanoparticles in this research. J. Chem. Biol. Interfaces 2013, Vol. 1, No /2013/1/053/005 doi: /jcbi

2 Selective Immobilization of Silver Nanoparticles In this research, we report on an efficient method for the selective immobilization of silver nanoparticles on a PTFE surface by using patterned graft polymerization based on ion irradiation. The process consisted of two steps: (1) the patterned surface graft polymerization of acrylic acid on the selectively-activated PTFE by ion irradiation and (2) the immobilization of silver nanoparticles on the grafted PTFE surface. The poly(acrylic acid) (PAA)-patterned PTFE surface was investigated in terms of the peroxide concentration, grafting degree, surface chemical structure, and wettability. Moreover, the selectively immobilized silver nanoparticles on the PAA-patterned PTFE surface were characterized by a scanning electron microscope with an energy dispersive X-ray spectrometer (SEM-EDX). Jung et al. in a 50% acetic acid solution, and then the optical densities of the resulting solutions were measured at 633 nm using a UV-Vis spectrophotometer (MQX 200 model, Bio- Tek Instruments, USA). The degree of grafting was calculated by the assumption that a carboxylic acid group in the AA combined with a TBO stoichiometrically. The chemical structures of the control, irradiated, and grafted films were analyzed by using attenuated total reflectance Fourier transform infrared spectroscope (ATR-FTIR, Tensor 37, Bruker) and the samples at a fluence of ions/cm 2 were used for this characterization of the irradiated and PAA-grafted PTFE. The wettability of the control, irradiated, and grafted films were examined by measuring water contact angles with a contact angle analyzer (Phoenix 300, Surface Electro Optics Company). EXPERIMENTAL DETAILS Immobilization of Silver Nanoparticles on the PAA-Patterned PTFE Preparation of Selectively PAA-Grafted PTFE Surface The immobilization of silver nanoparticles on the PAApatterned PTFE surfaces was performed by the similar PTFE (100 m thick, Nichias) films were irradiated with 150 kev H + method described in the literature. ions in the presence of a pattern mask (SUS, 27 The PAA-patterned PTFE films prepared at a fluence of m space, 150 m pitch) at fluences between 5 15 ions/cm 2 were and ions/cm 2 put into an aqueous AgNO. After irradiation, the irradiated PTFE films were exposed to air for 24 h to effec- 2 atmosphere. Thereafter, 3 (8 mm Showa Chemical) solution and stirred for 1 h under N tively generate peroxides on their irradiated surfaces. 24 the resulting films were rapidly immersed into an aqueous For 0.2 M NaBH graft polymerization, the irradiated samples were placed in 4 (Aldrich) solution. After stirring for 2 h, the films were washed several times with deionized water glass ampoules containing an aqueous IP: solution of 20On: vol% Sun, 08 andapr dried 2018 in a06:47:33 vacuum oven at 40 acrylic acid (AA, Aldrich), 0.2 M HCopyright: 2 SO 4 (Aldrich) American and C. The patterns of silver Scientific Publishers 0.1 wt% Mohr s salt ((NH 4 2 Fe(SO 4 2, Aldrich). Delivered The by Ingenta nanoparticles formed on the films were observed by ampoules were deaerated by purging with nitrogen gas for 30 min and then placed in a water bath at 65 C for 12 h. After heating, the resulting films were thoroughly washed with hot water to remove the formed homopolymers, and dried under vacuum at 50 C for 24 h. Surface Analysis The peroxide concentration on the irradiated PTFE surface was measured by a well-known 1,1-dipheyl-2- picryhydrazyl (DPPH) method described in the literature. 25 For this, the irradiated PTFE films were added into a DPPH/toluene solution ( mol/l) at 70 Cfor5h to decompose the peroxides formed on the surfaces. The consumed DPPH molecules were measured from the difference in the absorbance at 520 nm using S-1100 UV/Vis spectrophotometer (Scinco Co., Ltd., Korea) between the control and irradiated films. The grafting degree of the AA onto the PTFE films was determined by a Toluidine Blue O (TBO) staining method reported in the literature. 26 The grafted films were dipped into a 0.5 mm TBO solution at ph 10 and then constantly agitated for 6 h at room temperature. Afterwards, the TBO-stained films were thoroughly washed with an excess amount of sodium hydroxide solution (ph 10) to eliminate the free TBO molecules adhering to the surfaces. The TBO molecules complexed on the grafted PTFE surfaces were detached by dissolving a JEOL JSM-7500F scanning electron microscope (SEM) with an energy dispersive X-ray spectrometer (EDX). RESULTS AND DISCUSSION The schematic illustration for patterning silver nanoparticles on a polymer surface by using ion irradiation-induced grafting is described in Figure 1. First, the PTFE surface is irradiated by accelerated proton ions in the presence of a mask to selectively generate peroxides on the PTFE surface which can be as an initiator for graft polymerization. Subsequently, the graft polymerization of AA on the selectively irradiated PTFE is conducted by breaking the formed peroxide at an elevated temperature, and therefore, resulting in the formation of PAA patterns on the PTFE surface. Finally, the silver nanoparticles were selectively anchored on the PAA patterns on the PTFE surface via chemical reaction. The amounts of the peroxides formed on the irradiated PTFE films under various fluences were determined by a well-established DPPH method and the results are presented in Figure 1(a). The peroxide concentrations formed on the PTFE surfaces were increased with an increasing fluence because more radicals were generated on the surface at a higher fluence, and therefore, resulting in the higher generation of peroxides caused by an oxidation after exposed to air. 28 Moreover, the concentration of the 54 J. Chem. Biol. Interfaces 1, 53 57, 2013

3 Jung et al. Selective Immobilization of Silver Nanoparticles Figure 1. Schematic illustration for the selective immobilization of silver nanoparticle on the PTFE surface by ion beam-induced surface grafting. formed peroxides on the irradiated PTFE surfaces considerably affected the grafting degree on the surface because the peroxide worked as an initiator for graft polymerization of AA. Therefore, like the peroxide concentration, the grafting degree also increased with an increasing fluence and the highest grafting degree, 11.2 g/cm 2,was obtained for the PTFE film irradiated at a fluence of ions/cm 2 as shown in Figure 2(b). FTIR was employed to characterize the molecular structure of the PTFE after ion irradiation and graft polymerization and the results are shown in Figure 3. For the control PTFE in Figure 3(a), the characteristic absorption bands attributed to C F asymmetric and symmetric stretching vibrations in CF 2 groups were observed at about 1150 and 1240 cm 1, respectively. After ion irradiation, the FTIR spectrum was almost similar to that of IP: On: Sun, 08 theapr control 2018 PTFE. 06:47:33 On the other hand, for the PAA-grafted Copyright: American Scientific PTFE, the Publishers main characteristic bands of the grafted PAA Delivered by were Ingenta clearly detected at 3475 ( OH), 2930 ( CH), and 1710 cm 1 ( C O) in the spectrum of Figure 3(c). This result indicates that PAA was successfully grafted on the irradiated PTFE surface. The changes in the chemical nature of the PTFE surface after irradiation and graft polymerization was investigated by contact angle measurement and the results are present in Figure 4. The hydrophobic surface of the control PTFE exhibited a large water contact angle of around 105. In comparison to that of the control PTFE, the contact Figure 2. The peroxide concentration (a) and grafting degree (b) as a function of the fluence. Figure 3. FTIR spectra of the control (a), irradiated (b), and PAA-grafted PTFE films (c). J. Chem. Biol. Interfaces 1, 53 57,

4 Selective Immobilization of Silver Nanoparticles Jung et al. Figure 6. SEM images of the silver nanoparticle line/space patterns on the PAA-grafted PTFE and its corresponding EDX spectra for the line (b) and space (c) regions: The inset image in (a) represents the 3000 magnification of the dotted-circle. Figure 4. Variations in the water contact angles as a function of the fluence. angles of the irradiated PTFE were further reduced about 80 with an increasing fluence. After the graft polymerization of a hydrophilic AA, the contact angles were much more dropped up to 23 and depended on the grafting degree. This lower water contact angles of the PAA-grafted PTFE surfaces demonstrated that the hydrophobic PTFE surface was converted to the hydrophilic one by successful graft polymerization of hydrophilic AA on the irradiated surface. The formation of silver nanoparticles on the PAApatterned PTFE surface after the chemical IP: reduction On: of the Sun, 08 (C) Apr and 2018 fluorine 06:47:33 (F) of the PTFE substrate, indicating that AgNO 3 solution was confirmed by UV-Vis Copyright: spectroscopy. American Scientific the surface Publishers graft polymerization did not occur on the nonirradiated Ingenta regions on whose surface silver As shown in Figure 5, the PAA-grafted PTFEDelivered did not by nanoparticles show any absorption peak in the spectrum. However, in the spectrum of the silver nanoparticles (Ag)-immobilized PTFE, a symmetric absorption peak were clearly observed at approximately 420 nm (Fig. 5), which is the characteristic surface plasmon resonance of spherical silver nanoparticles. 27 Accordingly, the silver nanoparticles were effectively immobilized on the PAA-grafted PTFE surface. The silver nanoparticles immobilized on the PAAgrafted region of the PTFE surface were observed by SEM analysis. Figure 6(a) exhibits the resolved 50 m silver nanoparticles-immobilized patterns on the PTFE surface. The inset images in Figure 6(a) reveals that the surface of the control PTFE in the right part of the images was rather smooth surface but that of silver in the left part was very rough on which a lot of silver nanoparticles had been generated. In addition, to ascertain the silver immobilized only on the PAA grafted regions of the PTFE surfaces, the elemental content of the silver nanoparticles-immobilized PTFE surface was investigated by using EDX linked with SEM. As shown in Figure 6(c), the EDX spectrum for the space region between the silver nanoparticles-immobilized patterns showed only two peaks corresponding to carbon could not be immobilized. On the other hand, the EDX spectrum for the patterns (line) in Figure 6(b) exhibit three new peaks for carbon (C), oxygen (O), and silver (Ag) besides the C and F elements due to the immobilization of silver nanoparticles on the PAA-grafted region. Therefore, these results confirmed that the PAA were grafted on the irradiated regions of the PTFE surface and therefore silver nanoparticles were successfully formed only on the PAA-grafted regions of the PTFE surface. Figure 5. UV-Vis absorption spectra of the silver nanoparticle (Ag) immobilized on the PAA-grafted PTFE prepared by chemical reaction. CONCLUSIONS The selective immobilization of silver nanoparticles on a PTFE surface by using patterned graft polymerization based on ion irradiation was successfully demonstrated. The analytical results for the chemical structure and wettability authenticated the successful surface graft polymerization on the irradiated PTFE surface. In this grafting system, the peroxide concentration can be controlled by ion flunece, which can affect the grafting degree. It is obvious from the results of the UV-Vis and SEM- EDX analysis that the silver nanoparticles were successfully immobilized on the PAA-grafted regions of the PTFE surface. This technique can open up a new pathway for the formation of conductive patterns on a polymer substrate to be applicable to polymer electronic devices. 56 J. Chem. Biol. Interfaces 1, 53 57, 2013

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