- Email: [email protected]
Metallization of polymer through a novel surface modification applying a photocatalytic reaction
Surface & Coatings Technology 201 (2006) 3761 – 3766 www.elsevier.com/locate/surfcoat
Metallization of polymer through a novel surface modification applying a photocatalytic reaction Gyung Guk Kim a , Joung Ah Kang a , Ji Hui Kim a , Sun Jae Kim b , Nam Hee Lee b , Seon Jin Kim a,⁎ a
Division of Materials Science and Engineering, Hanyang University, 133-791, Republic of Korea b Department of Nano Science and Technology, Sejong University, 143-747, Republic of Korea Received 14 July 2006; accepted in revised form 14 September 2006 Available online 24 October 2006
Abstract The wet-chemical preconditioning process of polymers prior to metallization is generally performed with a strong acid bath such as a chromic, sulfuric or potassium- permanganate solution. Although the method is widely used in industrial applications, it results in undesirably environmental pollution and has inherent problems of uniformity and reproducibility for plating products. In the present study, a novel surface modification of a polymer utilizing the photocatalytic reaction in a P-25 dispersed solution and TiO2 sol prepared by a hydrothermal method was introduced to replace the wet-chemical pretreatment process which resulted in environmental pollution. Chemical changes in the surface were investigated with X-ray photoelectron spectroscopy (XPS). Analysis of the morphological changes was done by using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The surface modification method using the photocatalytic reaction in the presence of TiO2 particles resulted in excellent adhesion strength without a change of the surface morphology at the surface modification stage before electroless Cu plating for polymers. © 2006 Elsevier B.V. All rights reserved. Keywords: Photocatalytic reaction; Surface modification; Wet-chemical pretreatment; Glass epoxy resin
1. Introduction An interest in the deposition of metallic layers on polymers has gradually increased for either decorative or functional purposes in applications such as food packaging, microelectronics packaging, and coatings for EMI shielding and wear protection. Polymers are also used more and more in the automotive sector due to their light weights. Electroless metal deposition is one of the most frequently used industrial processes for metallizing insulators such as polymers [1–4]. Thus the deposition of a metallic coating on these parts enhances their range of application and creates a considerable added value. For metallization of polymers, surface modification processes are necessary to improve adhesion and surface seeding of an electroless catalyst. The conventional methods for surface modification are mechanical and wet-chemical methods to produce either chemical or morphological changes in the ⁎ Corresponding author. Tel.: +82 2 2220 0406; fax: +82 2 2293 7844. E-mail address: [email protected] (S.J. Kim). 0257-8972/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2006.09.052
surface. However, these processes have inherent problems of uniformity and reproducibility for plating products. Furthermore, they result in undesirable environmental pollution due to the aggressive acidic solutions such as chromic, sulfuric or potassium-permanganate solutions required to modify the surface of the polymer materials. Modification methods using plasma or laser as an alternative technique have the disadvantage of the large investment costs needed for commercialization. These environmental and economical limitations have increased the demand for the development of new, efficient, and dependable processes. Due to the high chemical stability, the low cost, and the possibility of using sunlight as the source of irradiation, the photocatalytic process, which is one of the advanced oxidation processes, is gradually receiving attention. As the surface of photocatalyst is irradiated with UV light, the process is initiated with the formation of electron/hole pairs by exciting electrons from the valence to the conduction band. In this photocatalytic reaction, the photogenerated holes react with water molecules and hydroxyl ions adsorbed on the surface of the photocatalyst
3762
G.G. Kim et al. / Surface & Coatings Technology 201 (2006) 3761–3766
Fig. 1. Schematic diagram of the apparatus used for the surface modification.
producing hydroxyl radicals. The resulting hydroxyl radicals act as very strong oxidizing agents and can oxidize most organic compounds and form the activated oxygen species such as – C_O, –OH, and –COOH [5–8]. In addition, these activated oxygen species are able to induce the hydrophile property which contributes to improve the adhesion strength of the electroless deposited film on the polymer surface [9]. So, it is possible that the photocatalytic reaction can be used to economically modify the polymer surfaces without environmental pollution. In the present study, the photocatalytic reaction in a P-25 dispersed solution and a TiO2 sol prepared by a hydrothermal method was investigated as a new approach for the surface modification of polymers.
The light source used was a mercury short arc lamp which emits its maximum radiation at the wavelength of 360 nm. UV light was irradiated for 15, 30, 60, and 120 min, and the intensity of incident light inside quartz cell was 120 mW/cm2. The conventional procedure of electroless Cu plating and the chemical composition of electroless Cu plating bath are shown in Fig. 2 (a) and (b), respectively. After the glass epoxy resin was irradiated by UV light in solution, it was rinsed twice with distilled water and finally immersed in the electroless Cu plating bath at 55–60 °C for 3 min. The Cu deposited substrate was thermally dried at 120 °C for 1 h in an oven. For Cu-patterning, the electroless Cu film was deposited after surface modification for either 15 min in a 1 M KMnO4 solution or for 1 h in TiO2 sol. The schematic illustration of the Cu-patterning process is shown in Fig. 3. Field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) were used to examine the change of surface morphology and the activated radical groups, respectively. The change of the contact angle on the substrates was measured to
2. Experimental procedure Glass epoxy resin, commonly used as the material for printed circuit boards, was chosen as a substrate for the surface modification before electroless Cu plating. An apparatus as shown in Fig. 1 was used for the surface modification of the glass epoxy resin. TiO2 sol was prepared by a hydrothermal method as follows [10]. Firstly, an aqueous solution of 0.1 M NH4OH was dropped slowly for 30 min into a 0.1 M TiOCl2 aqueous solution. The resulting Ti hydroxide was precipitated until the pH was equal to 7 and agitated for 1 h. After that, the hydroxide was repeatedly washed with distilled water to completely remove the chloride ions. The complete removal of chloride was confirmed through reaction between chloride ion in the waste water and an aqueous AgNO3 solution. Finally, the Ti hydroxide was dissolved in a 1.0 M hydrogen peroxide solution to obtain a yellow TiO2 precursor. Next, 400 ml of the TiO2 precursor was heated at 120 °C for 10 h in an autoclave (inner diameter 80 mm × height 120 mm). Also, conventional P-25 powder (Degussa Co. Ltd., 30 nm average particle size) having excellent photocatalytic activity was used as a reference to evaluate the ability for the surface modification of the hydrothermally prepared TiO2 sol. In the previous study, it was shown that the adhesion strength was excellent when the glass epoxy resin was modified in 0.01 g/L P-25 dispersed solution [11].
Fig. 2. (a) The procedure for electroless Cu plating and (b) the chemical composition of electroless Cu plating bath.
G.G. Kim et al. / Surface & Coatings Technology 201 (2006) 3761–3766
3763
achieved efficiently by the surface modification using the photocatalytic reaction and the surface roughness increased with the irradiated time. As demonstrated in Figs. 4 and 5, the photocatalytic reaction may lead to the change of surface morphology at the nano-scale. Thus, it is expected that the surface modification by the photocatalytic reaction in the presence of TiO2 particles may result in a more uniformly
Fig. 3. Schematic illustration of the Cu-patterning process.
confirm the hydrophile property caused by the photocatalytic reaction. The adhesion strength of the deposited Cu film was determined by using the scratch test with a 200 μm radius. 3. Results and discussion 3.1. Morphology studies of the modified surface Fig. 4 shows the FE-SEM images of the surface morphology before and after the surface modification using the photocatalytic reaction in a 0.01 g/L P-25 dispersed solution and a TiO2 sol. Fig. 4 (a) is the image of the glass epoxy resin before treatment and Fig. 4 (b) and (c) are images taken after the surface modification for 15 min in 0.01 g/L P-25 dispersed solution and for 1 h in TiO2 sol, respectively. In general, wetchemical pretreatment methods may result in morphological changes and the removal of weakly cohesive surface material resulting in severely rough and uneven surface morphology [8]. However, as shown in Fig. 4, the surface morphology after treating in the 0.01 g/L P-25 dispersed solution and the TiO2 sol showed almost no change in comparison with that before treatment. To examine the changes of the modified surface at the nanoscale, the modified surface after up to 2 h in TiO2 sol was also observed by AFM. As opposed to the FE-SEM images, the AFM images show that the photocatalytic reaction between TiO2 particles and substrate resulted in a change of surface morphology. Uniform conical surface structures could be
Fig. 4. FE-SEM micrographs of the surface of glass epoxy resin (a) before test, (b) after test for 15 min in 0.01 g/L P-25 dispersed solution, and (c) after test for 1 h in TiO2 sol.
3764
G.G. Kim et al. / Surface & Coatings Technology 201 (2006) 3761–3766
3.3. XPS analysis of the unmodified and the modified surface XPS analysis of the modified surface was performed to investigate other surface modification effects and clarify the reason for an improvement of the hydrophile properties. It was possible to observe which surface molecular structure was formed on the surface and how the occupancy ratio of carbon to oxygen on the surface was changed. Fig. 7 shows C1s XPS spectra of the glass epoxy resin before and after the photocatalytic reaction in the 0.01 g/L P-25 dispersed solution and in TiO2 sol measured by monochromatic Al-Kα X-ray excitation. The chemistry changes resulting from the photocatalytic reaction can be observed by comparing the C1s spectra before and after the surface modification. The spectra could be divided into five peaks although another peak developed after the surface modification. The changes of the intensities of the peaks were evaluated. Compared with the results before treating the surface, the peaks of species with oxygen such as C–O, C_O, –COO–, and O–C_O increased after the treatment. Namely, the amounts of initial species with oxygen increased more than those without oxygen and the oxidized species were more activated by the photocatalytic reaction. Meanwhile, the main carbon ring bonds such as C–C and C–H began to be broken and were oxidized rapidly with oxygen as the consequence of photocatalytic reaction in the presence of TiO2 particles. In addition, it has been shown that an increase of the peaks of the species with oxygen such as C–O, C_O, –COO–, and O–C_O increases the hydrophile property [8,9]. This implies that more activated oxygen species were formed on the modified surface by the photocatalytic reaction and the adhesion strength between the electroless Cu film and the glass epoxy resin may be improved by the hydrophile property resulting from the photocatalytic reaction. Fig. 5. AFM images of the modified surface for the glass epoxy resin; (a) before test, (b) after 1 h, and (c) after 2 h in TiO2 sol.
3.4. Adhesion strength of the deposited Cu film Fig. 8 shows the change of adhesion strength between the deposited Cu film and glass epoxy resin after the surface
deposited electroless Cu film compared to the wet-chemical method. 3.2. The change of contact angle after surface modification To evaluate the effect of the photocatalytic reaction on the surface modification, the contact angle was measured for the substrate before and after the surface modification in TiO2 sol. The initial contact angle before the surface modification was 83°, showing a hydrophobic surface. However, the contact angle after the surface modification decreased to 54°. This proves that the hydrophile property was induced on the modified surface by the photocatalytic reaction. The hydrophile property improves the wettability for the surface and leads to more intimate contact between the substrate and the electroless deposited film. Therefore, it is suggested that the photocatalytic reaction may contribute to improve the adhesion strength of the electroless deposited film on the polymer surface [9] (Fig. 6).
Fig. 6. The change of contact angle for glass epoxy resin after the photocatalytic reaction in TiO2 sol.
G.G. Kim et al. / Surface & Coatings Technology 201 (2006) 3761–3766
3765
Fig. 8. An increase of adhesion strength after the surface modification at different conditions.
irradiated with UV in deionized water in the absence of TiO2 was similar to that of the unmodified substrate. However, the adhesion strength of the modified substrate using the photocatalytic reaction in the presence of TiO2 particles was distinguishably improved. Even though it was not superior to that using 1 M KMnO4 solution, this means that the
Fig. 7. XPS analysis of the modified surface for the glass epoxy resin; (a) before test, (b) after test for 15 min in 0.01 g/L P-25 dispersed solution, and (c) after test for 1 h in TiO2 sol.
modification using the photochemical reaction under various conditions. The unmodified substrate was an electroless deposited Cu film, but the adhesion strength was poor in spite of thermal drying. The adhesion strength of the surface
Fig. 9. FE-SEM micrographs of Cu-patterned features after the electroless Cuplating and surface modification for (a) 15 min in a 1 M KMnO4 solution and (b) for 1 h in TiO2 sol.
3766
G.G. Kim et al. / Surface & Coatings Technology 201 (2006) 3761–3766
photocatalytic reaction between TiO2 particles and the substrate had a significant influence on the adhesion strength of the deposited Cu film. While the adhesion strength depended only slightly on the condition of TiO2 solution, it is presumed that the photocatalytic reactions for the surface modification in the hydrothermally prepared TiO2 sol was more activated than in the 0.01 g/L P-25 dispersed solution [10]. 3.5. The observation of Cu patterned features After the electroless Cu film was deposited on the modified surface for either 15 min in a 1 M KMnO4 solution or for 1 h in the TiO2 sol, the morphology of Cu-patterning was examined to observe the Cu patterned features with the surface modification methods. The Cu patterned features are shown in Fig. 9. Although there are no apparent differences, the deposited Cu film was formed more unevenly on the substrate treated with the 1 M KMnO4 solution than on the substrate treated with the TiO2 sol. In addition, it was possible to confirm that the morphologies on the deposited Cu film and in the vicinity of patterned lines are different for the two surface modification methods. Using the photocatalytic reaction, there were relatively smooth and uniform compared with that using the 1 M KMnO4 solution. It is considered that the photocatalytic reaction in the presence of TiO2 sol is able to modify the surface without a change of surface morphology as shown in Fig. 4. 4. Conclusions A study for the use of the photocatalytic reaction in the presence of TiO2 particles for a surface modification of glass epoxy resin was performed. The surface morphology after treating in the presence of TiO2 particles showed almost no change in comparison with that before treatment. As opposed to the surface modified in the 1 M KMnO4 solution, the deposited Cu film and Cu patterned features were relatively smooth and uniform when using TiO2. XPS results revealed that the main carbon ring bonds such as C–C and C–H began to be broken
and were oxidized rapidly with oxygen as a consequence of the photocatalytic reaction. Adhesion strength was more improved distinguishably when using the hydrothermally prepared TiO2 sol than when using only UV light irradiation in the absence of TiO2. Thus the photocatalytic reaction in the presence of TiO2 particles makes it possible to modify effectively the surface of polymer. And it is presumed that it may be applied to result in excellent adhesion strength without a change of the surface morphology. Acknowledgement This work has been carried out under the Cleaner Production Program supported by Korea National Cleaner Production Center, and supported by the SRC/ERC program of MOST/ KOSEF (R11-2000-067-01-002-0). References [1] G.O. Mallolry, J.B. Hajdu, Electroless Plating: Fundamentals and Applications, American Electroplaters and Surface Finishers Society, Orlando, FL, 1990. [2] K.L. Mittal, Metallized Plastics; 5 and 6 Fundamental and Applied Aspects, VSP, Utrecht, 1998. [3] L.T. Romankiw, Electrochim. Acta 42 (1997) 2985. [4] T.T. Mai, J.W. Schultze, G. Staikov, Electrochim. Acta 48 (2003) 3021. [5] V.A. Sakkas, I.M. Arabatzis, I.K. Konstaninou, A.D. Dimou, T.A. Albanis, P. Falaras, Appl. Catal. B. 49 (2004) 195. [6] S. Malato, J. Blanco, C. Richter, J. Gimenez, D. Curco, Water Sci. Technol. 35 (1997) 157. [7] O. Carp, C.L. Huisman, A. Reller, Prog. Solid State Chem. 32 (2004) 33. [8] I. Mathieson, R.H. Bradley, Int. J. Adhes. Adhes. 16 (1996) 29. [9] K.L. Mittal, A. Pizzi, Adhesion Promotion Techniques: Technological Applications, Marcel Dekker, New York, 1999. [10] Sun-Jae Kim, Doo-Sun Hwang, Nam-Hee Lee, Seunghan Shin, Seon-Jin Kim, Jpn. J. Appl. Phys. 44 (2005) 7703. [11] G.G. Kim, J.A. Kang, S.J. Kim, S.H. Shin, S.J. Kim, First International Symposium on Functional Materials, Kuala Lumpur, Malaysia, 2005, p. 32.
Metallization of polymer through a novel surface modification applying a photocatalytic reaction Gyung Guk Kim a , Joung Ah Kang a , Ji Hui Kim a , Sun Jae Kim b , Nam Hee Lee b , Seon Jin Kim a,⁎ a
Division of Materials Science and Engineering, Hanyang University, 133-791, Republic of Korea b Department of Nano Science and Technology, Sejong University, 143-747, Republic of Korea Received 14 July 2006; accepted in revised form 14 September 2006 Available online 24 October 2006
Abstract The wet-chemical preconditioning process of polymers prior to metallization is generally performed with a strong acid bath such as a chromic, sulfuric or potassium- permanganate solution. Although the method is widely used in industrial applications, it results in undesirably environmental pollution and has inherent problems of uniformity and reproducibility for plating products. In the present study, a novel surface modification of a polymer utilizing the photocatalytic reaction in a P-25 dispersed solution and TiO2 sol prepared by a hydrothermal method was introduced to replace the wet-chemical pretreatment process which resulted in environmental pollution. Chemical changes in the surface were investigated with X-ray photoelectron spectroscopy (XPS). Analysis of the morphological changes was done by using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The surface modification method using the photocatalytic reaction in the presence of TiO2 particles resulted in excellent adhesion strength without a change of the surface morphology at the surface modification stage before electroless Cu plating for polymers. © 2006 Elsevier B.V. All rights reserved. Keywords: Photocatalytic reaction; Surface modification; Wet-chemical pretreatment; Glass epoxy resin
1. Introduction An interest in the deposition of metallic layers on polymers has gradually increased for either decorative or functional purposes in applications such as food packaging, microelectronics packaging, and coatings for EMI shielding and wear protection. Polymers are also used more and more in the automotive sector due to their light weights. Electroless metal deposition is one of the most frequently used industrial processes for metallizing insulators such as polymers [1–4]. Thus the deposition of a metallic coating on these parts enhances their range of application and creates a considerable added value. For metallization of polymers, surface modification processes are necessary to improve adhesion and surface seeding of an electroless catalyst. The conventional methods for surface modification are mechanical and wet-chemical methods to produce either chemical or morphological changes in the ⁎ Corresponding author. Tel.: +82 2 2220 0406; fax: +82 2 2293 7844. E-mail address: [email protected] (S.J. Kim). 0257-8972/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2006.09.052
surface. However, these processes have inherent problems of uniformity and reproducibility for plating products. Furthermore, they result in undesirable environmental pollution due to the aggressive acidic solutions such as chromic, sulfuric or potassium-permanganate solutions required to modify the surface of the polymer materials. Modification methods using plasma or laser as an alternative technique have the disadvantage of the large investment costs needed for commercialization. These environmental and economical limitations have increased the demand for the development of new, efficient, and dependable processes. Due to the high chemical stability, the low cost, and the possibility of using sunlight as the source of irradiation, the photocatalytic process, which is one of the advanced oxidation processes, is gradually receiving attention. As the surface of photocatalyst is irradiated with UV light, the process is initiated with the formation of electron/hole pairs by exciting electrons from the valence to the conduction band. In this photocatalytic reaction, the photogenerated holes react with water molecules and hydroxyl ions adsorbed on the surface of the photocatalyst
3762
G.G. Kim et al. / Surface & Coatings Technology 201 (2006) 3761–3766
Fig. 1. Schematic diagram of the apparatus used for the surface modification.
producing hydroxyl radicals. The resulting hydroxyl radicals act as very strong oxidizing agents and can oxidize most organic compounds and form the activated oxygen species such as – C_O, –OH, and –COOH [5–8]. In addition, these activated oxygen species are able to induce the hydrophile property which contributes to improve the adhesion strength of the electroless deposited film on the polymer surface [9]. So, it is possible that the photocatalytic reaction can be used to economically modify the polymer surfaces without environmental pollution. In the present study, the photocatalytic reaction in a P-25 dispersed solution and a TiO2 sol prepared by a hydrothermal method was investigated as a new approach for the surface modification of polymers.
The light source used was a mercury short arc lamp which emits its maximum radiation at the wavelength of 360 nm. UV light was irradiated for 15, 30, 60, and 120 min, and the intensity of incident light inside quartz cell was 120 mW/cm2. The conventional procedure of electroless Cu plating and the chemical composition of electroless Cu plating bath are shown in Fig. 2 (a) and (b), respectively. After the glass epoxy resin was irradiated by UV light in solution, it was rinsed twice with distilled water and finally immersed in the electroless Cu plating bath at 55–60 °C for 3 min. The Cu deposited substrate was thermally dried at 120 °C for 1 h in an oven. For Cu-patterning, the electroless Cu film was deposited after surface modification for either 15 min in a 1 M KMnO4 solution or for 1 h in TiO2 sol. The schematic illustration of the Cu-patterning process is shown in Fig. 3. Field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) were used to examine the change of surface morphology and the activated radical groups, respectively. The change of the contact angle on the substrates was measured to
2. Experimental procedure Glass epoxy resin, commonly used as the material for printed circuit boards, was chosen as a substrate for the surface modification before electroless Cu plating. An apparatus as shown in Fig. 1 was used for the surface modification of the glass epoxy resin. TiO2 sol was prepared by a hydrothermal method as follows [10]. Firstly, an aqueous solution of 0.1 M NH4OH was dropped slowly for 30 min into a 0.1 M TiOCl2 aqueous solution. The resulting Ti hydroxide was precipitated until the pH was equal to 7 and agitated for 1 h. After that, the hydroxide was repeatedly washed with distilled water to completely remove the chloride ions. The complete removal of chloride was confirmed through reaction between chloride ion in the waste water and an aqueous AgNO3 solution. Finally, the Ti hydroxide was dissolved in a 1.0 M hydrogen peroxide solution to obtain a yellow TiO2 precursor. Next, 400 ml of the TiO2 precursor was heated at 120 °C for 10 h in an autoclave (inner diameter 80 mm × height 120 mm). Also, conventional P-25 powder (Degussa Co. Ltd., 30 nm average particle size) having excellent photocatalytic activity was used as a reference to evaluate the ability for the surface modification of the hydrothermally prepared TiO2 sol. In the previous study, it was shown that the adhesion strength was excellent when the glass epoxy resin was modified in 0.01 g/L P-25 dispersed solution [11].
Fig. 2. (a) The procedure for electroless Cu plating and (b) the chemical composition of electroless Cu plating bath.
G.G. Kim et al. / Surface & Coatings Technology 201 (2006) 3761–3766
3763
achieved efficiently by the surface modification using the photocatalytic reaction and the surface roughness increased with the irradiated time. As demonstrated in Figs. 4 and 5, the photocatalytic reaction may lead to the change of surface morphology at the nano-scale. Thus, it is expected that the surface modification by the photocatalytic reaction in the presence of TiO2 particles may result in a more uniformly
Fig. 3. Schematic illustration of the Cu-patterning process.
confirm the hydrophile property caused by the photocatalytic reaction. The adhesion strength of the deposited Cu film was determined by using the scratch test with a 200 μm radius. 3. Results and discussion 3.1. Morphology studies of the modified surface Fig. 4 shows the FE-SEM images of the surface morphology before and after the surface modification using the photocatalytic reaction in a 0.01 g/L P-25 dispersed solution and a TiO2 sol. Fig. 4 (a) is the image of the glass epoxy resin before treatment and Fig. 4 (b) and (c) are images taken after the surface modification for 15 min in 0.01 g/L P-25 dispersed solution and for 1 h in TiO2 sol, respectively. In general, wetchemical pretreatment methods may result in morphological changes and the removal of weakly cohesive surface material resulting in severely rough and uneven surface morphology [8]. However, as shown in Fig. 4, the surface morphology after treating in the 0.01 g/L P-25 dispersed solution and the TiO2 sol showed almost no change in comparison with that before treatment. To examine the changes of the modified surface at the nanoscale, the modified surface after up to 2 h in TiO2 sol was also observed by AFM. As opposed to the FE-SEM images, the AFM images show that the photocatalytic reaction between TiO2 particles and substrate resulted in a change of surface morphology. Uniform conical surface structures could be
Fig. 4. FE-SEM micrographs of the surface of glass epoxy resin (a) before test, (b) after test for 15 min in 0.01 g/L P-25 dispersed solution, and (c) after test for 1 h in TiO2 sol.
3764
G.G. Kim et al. / Surface & Coatings Technology 201 (2006) 3761–3766
3.3. XPS analysis of the unmodified and the modified surface XPS analysis of the modified surface was performed to investigate other surface modification effects and clarify the reason for an improvement of the hydrophile properties. It was possible to observe which surface molecular structure was formed on the surface and how the occupancy ratio of carbon to oxygen on the surface was changed. Fig. 7 shows C1s XPS spectra of the glass epoxy resin before and after the photocatalytic reaction in the 0.01 g/L P-25 dispersed solution and in TiO2 sol measured by monochromatic Al-Kα X-ray excitation. The chemistry changes resulting from the photocatalytic reaction can be observed by comparing the C1s spectra before and after the surface modification. The spectra could be divided into five peaks although another peak developed after the surface modification. The changes of the intensities of the peaks were evaluated. Compared with the results before treating the surface, the peaks of species with oxygen such as C–O, C_O, –COO–, and O–C_O increased after the treatment. Namely, the amounts of initial species with oxygen increased more than those without oxygen and the oxidized species were more activated by the photocatalytic reaction. Meanwhile, the main carbon ring bonds such as C–C and C–H began to be broken and were oxidized rapidly with oxygen as the consequence of photocatalytic reaction in the presence of TiO2 particles. In addition, it has been shown that an increase of the peaks of the species with oxygen such as C–O, C_O, –COO–, and O–C_O increases the hydrophile property [8,9]. This implies that more activated oxygen species were formed on the modified surface by the photocatalytic reaction and the adhesion strength between the electroless Cu film and the glass epoxy resin may be improved by the hydrophile property resulting from the photocatalytic reaction. Fig. 5. AFM images of the modified surface for the glass epoxy resin; (a) before test, (b) after 1 h, and (c) after 2 h in TiO2 sol.
3.4. Adhesion strength of the deposited Cu film Fig. 8 shows the change of adhesion strength between the deposited Cu film and glass epoxy resin after the surface
deposited electroless Cu film compared to the wet-chemical method. 3.2. The change of contact angle after surface modification To evaluate the effect of the photocatalytic reaction on the surface modification, the contact angle was measured for the substrate before and after the surface modification in TiO2 sol. The initial contact angle before the surface modification was 83°, showing a hydrophobic surface. However, the contact angle after the surface modification decreased to 54°. This proves that the hydrophile property was induced on the modified surface by the photocatalytic reaction. The hydrophile property improves the wettability for the surface and leads to more intimate contact between the substrate and the electroless deposited film. Therefore, it is suggested that the photocatalytic reaction may contribute to improve the adhesion strength of the electroless deposited film on the polymer surface [9] (Fig. 6).
Fig. 6. The change of contact angle for glass epoxy resin after the photocatalytic reaction in TiO2 sol.
G.G. Kim et al. / Surface & Coatings Technology 201 (2006) 3761–3766
3765
Fig. 8. An increase of adhesion strength after the surface modification at different conditions.
irradiated with UV in deionized water in the absence of TiO2 was similar to that of the unmodified substrate. However, the adhesion strength of the modified substrate using the photocatalytic reaction in the presence of TiO2 particles was distinguishably improved. Even though it was not superior to that using 1 M KMnO4 solution, this means that the
Fig. 7. XPS analysis of the modified surface for the glass epoxy resin; (a) before test, (b) after test for 15 min in 0.01 g/L P-25 dispersed solution, and (c) after test for 1 h in TiO2 sol.
modification using the photochemical reaction under various conditions. The unmodified substrate was an electroless deposited Cu film, but the adhesion strength was poor in spite of thermal drying. The adhesion strength of the surface
Fig. 9. FE-SEM micrographs of Cu-patterned features after the electroless Cuplating and surface modification for (a) 15 min in a 1 M KMnO4 solution and (b) for 1 h in TiO2 sol.
3766
G.G. Kim et al. / Surface & Coatings Technology 201 (2006) 3761–3766
photocatalytic reaction between TiO2 particles and the substrate had a significant influence on the adhesion strength of the deposited Cu film. While the adhesion strength depended only slightly on the condition of TiO2 solution, it is presumed that the photocatalytic reactions for the surface modification in the hydrothermally prepared TiO2 sol was more activated than in the 0.01 g/L P-25 dispersed solution [10]. 3.5. The observation of Cu patterned features After the electroless Cu film was deposited on the modified surface for either 15 min in a 1 M KMnO4 solution or for 1 h in the TiO2 sol, the morphology of Cu-patterning was examined to observe the Cu patterned features with the surface modification methods. The Cu patterned features are shown in Fig. 9. Although there are no apparent differences, the deposited Cu film was formed more unevenly on the substrate treated with the 1 M KMnO4 solution than on the substrate treated with the TiO2 sol. In addition, it was possible to confirm that the morphologies on the deposited Cu film and in the vicinity of patterned lines are different for the two surface modification methods. Using the photocatalytic reaction, there were relatively smooth and uniform compared with that using the 1 M KMnO4 solution. It is considered that the photocatalytic reaction in the presence of TiO2 sol is able to modify the surface without a change of surface morphology as shown in Fig. 4. 4. Conclusions A study for the use of the photocatalytic reaction in the presence of TiO2 particles for a surface modification of glass epoxy resin was performed. The surface morphology after treating in the presence of TiO2 particles showed almost no change in comparison with that before treatment. As opposed to the surface modified in the 1 M KMnO4 solution, the deposited Cu film and Cu patterned features were relatively smooth and uniform when using TiO2. XPS results revealed that the main carbon ring bonds such as C–C and C–H began to be broken
and were oxidized rapidly with oxygen as a consequence of the photocatalytic reaction. Adhesion strength was more improved distinguishably when using the hydrothermally prepared TiO2 sol than when using only UV light irradiation in the absence of TiO2. Thus the photocatalytic reaction in the presence of TiO2 particles makes it possible to modify effectively the surface of polymer. And it is presumed that it may be applied to result in excellent adhesion strength without a change of the surface morphology. Acknowledgement This work has been carried out under the Cleaner Production Program supported by Korea National Cleaner Production Center, and supported by the SRC/ERC program of MOST/ KOSEF (R11-2000-067-01-002-0). References [1] G.O. Mallolry, J.B. Hajdu, Electroless Plating: Fundamentals and Applications, American Electroplaters and Surface Finishers Society, Orlando, FL, 1990. [2] K.L. Mittal, Metallized Plastics; 5 and 6 Fundamental and Applied Aspects, VSP, Utrecht, 1998. [3] L.T. Romankiw, Electrochim. Acta 42 (1997) 2985. [4] T.T. Mai, J.W. Schultze, G. Staikov, Electrochim. Acta 48 (2003) 3021. [5] V.A. Sakkas, I.M. Arabatzis, I.K. Konstaninou, A.D. Dimou, T.A. Albanis, P. Falaras, Appl. Catal. B. 49 (2004) 195. [6] S. Malato, J. Blanco, C. Richter, J. Gimenez, D. Curco, Water Sci. Technol. 35 (1997) 157. [7] O. Carp, C.L. Huisman, A. Reller, Prog. Solid State Chem. 32 (2004) 33. [8] I. Mathieson, R.H. Bradley, Int. J. Adhes. Adhes. 16 (1996) 29. [9] K.L. Mittal, A. Pizzi, Adhesion Promotion Techniques: Technological Applications, Marcel Dekker, New York, 1999. [10] Sun-Jae Kim, Doo-Sun Hwang, Nam-Hee Lee, Seunghan Shin, Seon-Jin Kim, Jpn. J. Appl. Phys. 44 (2005) 7703. [11] G.G. Kim, J.A. Kang, S.J. Kim, S.H. Shin, S.J. Kim, First International Symposium on Functional Materials, Kuala Lumpur, Malaysia, 2005, p. 32.