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Analysis of hydrophile process of a polymer surface with an inverter plasma
Surface and Coatings Technology 136 Ž2001. 265᎐268
Analysis of hydrophile process of a polymer surface with an inverter plasma Nariaki Murakami a , Katsutoshi Tanakaa , Satoshi Sugimotob,U , Masato Kiuchi a , Seiichi Goto a a
Plasma Physics Laboratory, Graduate School of Engineering, Osaka Uni¨ ersity, 2-1Yamadaoka, Suita, Osaka 565-0871, Japan b Osaka National Research Institute, 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan
Abstract An analysis of the hydrophile process of a polymer surface was performed with a discharge system composed of an inverter power supply and a pair of insulated parallel electrodes. Using this discharge system, we could produce a narrow-pulsed plasma for which the direction of the applied electric field could be controlled. Contact angle and XPS measurements were performed to analyze the surface of the treated polymer films. In the case of a unipolar pulse operation, the electric field direction toward to the sample surface was more effective to prepare a hydrophilic polymer surface than the opposite one. In the case of a bipolar pulse operation, the contact angle decreased. This observation is important for a better understanding of the hydrophile process. 䊚 2001 Elsevier Science B.V. All rights reserved. Keywords: Surface treatment; Low-density-polyethylene; Contact angle; Hydrophile process; Inverter plasma; Positive ion; Surface reaction; XPS
1. Introduction Plasma surface modification of polymers is a useful method for hydrophile processing by which their adhesion properties can be improved w1᎐4x. Investigation of the treated polymers by surface analysis techniques has revealed that the hydrophile processing is performed by surface reactions, mostly oxidation with the help of electrons, ions, atoms, photons, ozone, and radicals w5᎐8x. However, it is not clear how each kind of particle behaves during the exposure of a polymer surface to a plasma because it is considerably difficult to control the particles separately in plasmas produced conventionally. We have developed a low-frequency pulsed discharge
U
Corresponding author. Tel.: q81-6-6879-7912; fax: q81-6-68797916. E-mail address: [email protected] ŽS. Sugimoto..
system using a high-voltage inverter power supply w9x. A high-voltage bipolar pulse train from the inverter power supply generates an alternating electric field around a reaction region. This electric field plays a role of gas excitation and simultaneously accelerates the charged particles, i.e. the ions and the electrons. Because such an acceleration effect is expected to be advantageous for plasma processing w10x, we call plasma produced by this discharge style inverter plasma. In this work, we have studied a hydrophile process of a polymer surface using the inverter discharge system. Normally, bipolar output pulses are used for processing with this discharge system Žbipolar mode.. As a special case, the only positive or negative output pulse can also be utilized Žunipolar mode.. Using these two modes, it must be possible to enhance the behavior of charged particles in the plasma. In this paper, we describe a configuration of the inverter plasma processing system. We then show the measurement results of samples treated on various pulsing conditions and a correlation
0257-8972r01r$ - see front matter 䊚 2001 Elsevier Science B.V. All rights reserved. PII: S 0 2 5 7 - 8 9 7 2 Ž 0 0 . 0 1 0 2 8 - 8
N. Murakami et al. r Surface and Coatings Technology 136 (2001) 265᎐268
266
Fig. 1. Schematic diagram of inverter plasma discharge system.
between the hydrophile process and the directions of the applied electric field.
2. Experimental system Fig. 1 shows a schematic diagram of the inverter plasma processing system. The output of the high-voltage inverter power supply is connected to the upper electrode plate with respect to the bottom plate, which is grounded. The waveform applied to the upper electrode is a pulse train consisting of either positive unipolar pulses, negative ones, or alternating bipolar pulses. The pulse height for both polarities can be varied independently in a range of 0᎐480 V. The samples, additive-free low-density polyethylene ŽLDPE, Mitsubishi Chemical Corporation. film pieces of 20 = 20 = 0.1 mm, were cleaned in a Soxhlet with methyl alcohol for 20 h. One of these sample film
Fig. 2. Schematic view of electrodes with electrode covers.
Fig. 3. Narrow-pulsed plasma produced with the inverter discharge system. Ža. Typical waveforms of the discharge voltage Vd and current Id . The positive pulse height and the negative one are q550 V and y550 V, respectively. Žb. Photograph of a plasma produced under the same conditions as Ža..
pieces was fixed on the bottom electrode plate. The vacuum chamber was evacuated to a base pressure of less than 10 Pa by the rotary pump. After the argon gas was fed into the vacuum chamber at a pressure of 450 Pa, the plasma was produced between the electrode plates. The electrodes, 30 mm in diameter, were mounted facing each other in parallel. Because the direct current Ždc. was not drawn through the polymer sample, no dc plasma was produced on the sample surface. In addition, because the polymer sample was electrically floating, the electric field on the sample surface was not specified. Then, we installed insulating covers to the electrodes, as shown in Fig. 2. By these covers, any dc component was blocked and only the narrow-pulsed charge current flowed. Fig. 3a shows typical waveforms of the discharge voltage and the discharge current between the electrodes. Although the width of the charge current pulse was observed to be less than 50 ns, plasma was successfully produced between the electrodes as shown in Fig. 3b. Thus, the intensity and the direction of an electric field on the sample surface can considerably relate to those of an applied electric field between the electrodes during such charge term.
N. Murakami et al. r Surface and Coatings Technology 136 (2001) 265᎐268
267
Table 1 Contact angles when the same number of plasma pulses Žq240, y240. are applied to the LDPE surface Plasma exposure time Žs.
Repeating frequency ŽKHz.
Ž0. 30 60 300
10 5.0 1.0
a
Plasma pulses
Contact angle Ždegree.
Ž0. 30 = 104 30 = 104 30 = 104
Ž98.a 58 " 2 57 " 1 57 " 2
Untreated sample.
Two different measurements were used for surface analysis of the treated films. One was a measurement of the contact angle value of water. The measured data were obtained by averaging five contact angle values for five samples, which were treated under the same conditions. The other was the X-ray photoelectron spectroscopy ŽXPS. in which a Mg K ␣ radiation Ž1523.6 eV. was used as the excitation source. Table 1 shows the water contact angle obtained for cases where the same number of plasma pulses were applied to the LDPE surface with the inverter operating in the bipolar mode Žq240, y240., where ŽqV1 , yV2 . means a pulse height combination of the bipolar pulse with the positive height of V1 volts and the negative one of V2 volts. The obtained contact angles are very similar. It was found that the amount of the reaction on the sample surface depended only on the pulse number and not on the plasma exposure time or repeating frequency, independently. This result indicates that the inverter irradiation system has good reproducibility for an isolated surface such as the LDPE film.
Fig. 4. Change in the water contact angle of LDPE surface with different voltage inverter plasmas: circle signs are for the conditions that the positive pulse height is fixed at q480 V, and the negative one yVa is varied from 0 to y480 V; triangle signs are for the conditions that the negative pulse height is fixed at y480 V, and the positive one qVa is varied from 0 to q480 V.
ing in the bipolar mode can produce highly wettable LDPE surfaces of qualities as good as has ever been done w11,12x. Fig. 5 shows the wide scan XPS data. The spectrum Ža. in Fig. 5 indicates data for the untreated LDPE. The spectra Žb᎐d. indicate those for the treated LDPE for the pulsing conditions of Žq480, y0., Žq0, y480., and Žq480, y480., respectively. Notice that a major carbon line ŽC 1s. can be seen in the spectrum Ža. in Fig. 5 for untreated LDPE, and that the oxygen line ŽO 1s. is much smaller than the carbon line ŽC 1s.. In every spectra Žb᎐d. in Fig. 5 for the treated LDPE, the oxygen ŽO 1s. signal is also detected. The intensity of the oxygen line ŽO 1s. becomes bigger in the order, Žq0, y480., Žq480, y0., Žq480, y480. pulsing conditions. The C 1s line consists of chemically shifted species:
3. Results and discussion Fig. 4 shows the contact angles obtained for the cases of Žq480, yVa . and ŽqVa , y480. pulsing conditions. Here, the positive or negative pulse height was fixed at 480 V and the opposite pulse height Va was changed between 0 and 480 V. The samples were irradiated for 3 min at a repeating frequency of 10 KHz. It was considered that the surface processing was mostly saturated with this amount of irradiation from the contact angle observation. On the axis of Va s 0, the pulsing conditions correspond to the unipolar mode. In these cases, the only positive pulse Žq480, 0. or the only negative one Ž0, y480. resulted in the contact angles of 46 and 68⬚, respectively. In the cases of the bipolar mode, the contact angles continuously decreased as Va increased and reached 29⬚ for the Žq480, y480. pulsing condition. This result shows that the inverter plasma process-
Fig. 5. Wide scan XPS spectra of LDPE samples: Ža. untreated, Žb᎐d. treated with inverter plasma under the pulsing conditions of Žq480, y0., Žq0,y480., and Žq480, y0., respectively.
268
N. Murakami et al. r Surface and Coatings Technology 136 (2001) 265᎐268
Plasma properties, such as plasma density, depend on the pulsing conditions. Thus, the processing condition, in particular, the processing speed, is not the same for the different pulsing conditions. In fact, the experimental plots in Fig. 4 show a little non-monotonically decreasing behavior. However, because every plasma exposure was performed until the surface reaction was saturated, most of the differences on the treated sample surface must arise, not from the reaction speed, but the reaction mechanism of the hydrophile process.
4. Conclusion
Fig. 6. Narrow scan XPS spectra around the carbon line ŽC 1s. of LDPE samples: Ža. untreated; Žb᎐d. treated with inverter plasma in the pulsing conditions of Žq480, y0., Žq0, y480., and Žq480, y0., respectively. The full width at half maximum of each line profile is also shown.
alcohol at 1᎐2 eV; ester at 1᎐3 eV; ketone at 2᎐3 eV; aldehyde at 2᎐3 eV; and carboxylic at 3᎐4 eV from the C᎐C component. The narrow scan of the same XPS spectra around the carbon line ŽC 1s, 285 eV. is shown in Fig. 6. The full widths at half maximum of the carbon line for the spectra Ža᎐d. in Fig. 6 are 1.1, 1.6, 1.3 and 1.9 ŽeV., respectively. It can clearly be seen that the amount of some oxygen-containing species incorporated onto the surface carbons become bigger in the order: Žq0, y480., Žq480, y0., Žq480, y480. pulsing conditions. Moreover, a strong presence of other lines, which are not yet specified, is also observed in spectrum Žd. for the Žq480, y480. pulsing condition. Generally speaking, polymer surfaces treated with argon glow plasmas have hydrophilic species Ž ᎐OH and ᎐COOH, etc.. introduced to the surface. When positive ions, which have a large momentum compared to that of electron came into collision with the sample surface, more C᎐H combinations are cut off and hydrophilic processing is accomplished more effectively. In the bipolar case Žq480, y480., both electrons and positive ions collided with the sample surface by turns and the hydrophile process was much more effective.
In this work, we have presented results on the hydrophile process using an inverter discharge system and the first correlation of the contact angle with the pulsing conditions. In particular, we have shown that a positive polarity of the voltage applied to the counter electrode is much more effective for hydrophile processing than a negative one. It also seems that a cooperation effect between ions and electrons exists in this surface process, which may be important for a further understanding of a hydrophile process. References w1x J.M. Burksarand, J. Vac. Sci. Technol. 15 Ž1978. 223᎐226. w2x W.L. Wade Jr., R.J. Mammone, M. Binder, J. Appl. Polym. Sci. 43 Ž1991. 1589᎐1591. w3x R.K. Wells, J.P.S. Badyal, I.W. Drummond, K.S. Robinson, F.J. Street, J. Adhes. Sci. Technol. 7 Ž1993. 1129᎐1137. w4x H. Guezenoc, Y. Segui, K. Asfardjani, S. Thery, J. Adhes. Sci. Technol. 7 Ž1993. 953᎐965. w5x D.T. Clark, A. Dilks, J. Polym. Sci, Polym. Chem. Ed. 15 Ž1977. 15᎐30. w6x F. Denes, R.A. Young, M. Sarmadi, J. Photopolym. Sci. 10 Ž1997. 91᎐112. w7x L.J. Gerenser, J. Adhes. Sci. Technol. 7 Ž1993. 1019᎐1040. w8x E. Occhiello, M. Morra, F. Garbassi, D. Johnson, P. Humphrey, Appl. Surf. Sci. 47 Ž1991. 235᎐242. w9x S. Sugimoto, M. Kiuchi, S. Takechi, K. Tanaka, S. Goto, Proc. PBII-99, to appear in Surf. Coat. Technol. w10x M. Kiuchi, K. Tanaka, S. Takechi, S. Sugimoto, S. Goto, Proc. PBII-99, to appear in Surf. Coat. Technol. w11x J.G.A. Terlingen, H.F.C. Geritsen, J. Feijen, A.S. Hoffman, J. Appl. Polym. Sci. 57 Ž1995. 969᎐982. w12x Y. Ikada, T. Matsunage, M. Suzuki, Nippon Kagaku Kaishi 1985 Ž1985. 1079᎐1086.
Analysis of hydrophile process of a polymer surface with an inverter plasma Nariaki Murakami a , Katsutoshi Tanakaa , Satoshi Sugimotob,U , Masato Kiuchi a , Seiichi Goto a a
Plasma Physics Laboratory, Graduate School of Engineering, Osaka Uni¨ ersity, 2-1Yamadaoka, Suita, Osaka 565-0871, Japan b Osaka National Research Institute, 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan
Abstract An analysis of the hydrophile process of a polymer surface was performed with a discharge system composed of an inverter power supply and a pair of insulated parallel electrodes. Using this discharge system, we could produce a narrow-pulsed plasma for which the direction of the applied electric field could be controlled. Contact angle and XPS measurements were performed to analyze the surface of the treated polymer films. In the case of a unipolar pulse operation, the electric field direction toward to the sample surface was more effective to prepare a hydrophilic polymer surface than the opposite one. In the case of a bipolar pulse operation, the contact angle decreased. This observation is important for a better understanding of the hydrophile process. 䊚 2001 Elsevier Science B.V. All rights reserved. Keywords: Surface treatment; Low-density-polyethylene; Contact angle; Hydrophile process; Inverter plasma; Positive ion; Surface reaction; XPS
1. Introduction Plasma surface modification of polymers is a useful method for hydrophile processing by which their adhesion properties can be improved w1᎐4x. Investigation of the treated polymers by surface analysis techniques has revealed that the hydrophile processing is performed by surface reactions, mostly oxidation with the help of electrons, ions, atoms, photons, ozone, and radicals w5᎐8x. However, it is not clear how each kind of particle behaves during the exposure of a polymer surface to a plasma because it is considerably difficult to control the particles separately in plasmas produced conventionally. We have developed a low-frequency pulsed discharge
U
Corresponding author. Tel.: q81-6-6879-7912; fax: q81-6-68797916. E-mail address: [email protected] ŽS. Sugimoto..
system using a high-voltage inverter power supply w9x. A high-voltage bipolar pulse train from the inverter power supply generates an alternating electric field around a reaction region. This electric field plays a role of gas excitation and simultaneously accelerates the charged particles, i.e. the ions and the electrons. Because such an acceleration effect is expected to be advantageous for plasma processing w10x, we call plasma produced by this discharge style inverter plasma. In this work, we have studied a hydrophile process of a polymer surface using the inverter discharge system. Normally, bipolar output pulses are used for processing with this discharge system Žbipolar mode.. As a special case, the only positive or negative output pulse can also be utilized Žunipolar mode.. Using these two modes, it must be possible to enhance the behavior of charged particles in the plasma. In this paper, we describe a configuration of the inverter plasma processing system. We then show the measurement results of samples treated on various pulsing conditions and a correlation
0257-8972r01r$ - see front matter 䊚 2001 Elsevier Science B.V. All rights reserved. PII: S 0 2 5 7 - 8 9 7 2 Ž 0 0 . 0 1 0 2 8 - 8
N. Murakami et al. r Surface and Coatings Technology 136 (2001) 265᎐268
266
Fig. 1. Schematic diagram of inverter plasma discharge system.
between the hydrophile process and the directions of the applied electric field.
2. Experimental system Fig. 1 shows a schematic diagram of the inverter plasma processing system. The output of the high-voltage inverter power supply is connected to the upper electrode plate with respect to the bottom plate, which is grounded. The waveform applied to the upper electrode is a pulse train consisting of either positive unipolar pulses, negative ones, or alternating bipolar pulses. The pulse height for both polarities can be varied independently in a range of 0᎐480 V. The samples, additive-free low-density polyethylene ŽLDPE, Mitsubishi Chemical Corporation. film pieces of 20 = 20 = 0.1 mm, were cleaned in a Soxhlet with methyl alcohol for 20 h. One of these sample film
Fig. 2. Schematic view of electrodes with electrode covers.
Fig. 3. Narrow-pulsed plasma produced with the inverter discharge system. Ža. Typical waveforms of the discharge voltage Vd and current Id . The positive pulse height and the negative one are q550 V and y550 V, respectively. Žb. Photograph of a plasma produced under the same conditions as Ža..
pieces was fixed on the bottom electrode plate. The vacuum chamber was evacuated to a base pressure of less than 10 Pa by the rotary pump. After the argon gas was fed into the vacuum chamber at a pressure of 450 Pa, the plasma was produced between the electrode plates. The electrodes, 30 mm in diameter, were mounted facing each other in parallel. Because the direct current Ždc. was not drawn through the polymer sample, no dc plasma was produced on the sample surface. In addition, because the polymer sample was electrically floating, the electric field on the sample surface was not specified. Then, we installed insulating covers to the electrodes, as shown in Fig. 2. By these covers, any dc component was blocked and only the narrow-pulsed charge current flowed. Fig. 3a shows typical waveforms of the discharge voltage and the discharge current between the electrodes. Although the width of the charge current pulse was observed to be less than 50 ns, plasma was successfully produced between the electrodes as shown in Fig. 3b. Thus, the intensity and the direction of an electric field on the sample surface can considerably relate to those of an applied electric field between the electrodes during such charge term.
N. Murakami et al. r Surface and Coatings Technology 136 (2001) 265᎐268
267
Table 1 Contact angles when the same number of plasma pulses Žq240, y240. are applied to the LDPE surface Plasma exposure time Žs.
Repeating frequency ŽKHz.
Ž0. 30 60 300
10 5.0 1.0
a
Plasma pulses
Contact angle Ždegree.
Ž0. 30 = 104 30 = 104 30 = 104
Ž98.a 58 " 2 57 " 1 57 " 2
Untreated sample.
Two different measurements were used for surface analysis of the treated films. One was a measurement of the contact angle value of water. The measured data were obtained by averaging five contact angle values for five samples, which were treated under the same conditions. The other was the X-ray photoelectron spectroscopy ŽXPS. in which a Mg K ␣ radiation Ž1523.6 eV. was used as the excitation source. Table 1 shows the water contact angle obtained for cases where the same number of plasma pulses were applied to the LDPE surface with the inverter operating in the bipolar mode Žq240, y240., where ŽqV1 , yV2 . means a pulse height combination of the bipolar pulse with the positive height of V1 volts and the negative one of V2 volts. The obtained contact angles are very similar. It was found that the amount of the reaction on the sample surface depended only on the pulse number and not on the plasma exposure time or repeating frequency, independently. This result indicates that the inverter irradiation system has good reproducibility for an isolated surface such as the LDPE film.
Fig. 4. Change in the water contact angle of LDPE surface with different voltage inverter plasmas: circle signs are for the conditions that the positive pulse height is fixed at q480 V, and the negative one yVa is varied from 0 to y480 V; triangle signs are for the conditions that the negative pulse height is fixed at y480 V, and the positive one qVa is varied from 0 to q480 V.
ing in the bipolar mode can produce highly wettable LDPE surfaces of qualities as good as has ever been done w11,12x. Fig. 5 shows the wide scan XPS data. The spectrum Ža. in Fig. 5 indicates data for the untreated LDPE. The spectra Žb᎐d. indicate those for the treated LDPE for the pulsing conditions of Žq480, y0., Žq0, y480., and Žq480, y480., respectively. Notice that a major carbon line ŽC 1s. can be seen in the spectrum Ža. in Fig. 5 for untreated LDPE, and that the oxygen line ŽO 1s. is much smaller than the carbon line ŽC 1s.. In every spectra Žb᎐d. in Fig. 5 for the treated LDPE, the oxygen ŽO 1s. signal is also detected. The intensity of the oxygen line ŽO 1s. becomes bigger in the order, Žq0, y480., Žq480, y0., Žq480, y480. pulsing conditions. The C 1s line consists of chemically shifted species:
3. Results and discussion Fig. 4 shows the contact angles obtained for the cases of Žq480, yVa . and ŽqVa , y480. pulsing conditions. Here, the positive or negative pulse height was fixed at 480 V and the opposite pulse height Va was changed between 0 and 480 V. The samples were irradiated for 3 min at a repeating frequency of 10 KHz. It was considered that the surface processing was mostly saturated with this amount of irradiation from the contact angle observation. On the axis of Va s 0, the pulsing conditions correspond to the unipolar mode. In these cases, the only positive pulse Žq480, 0. or the only negative one Ž0, y480. resulted in the contact angles of 46 and 68⬚, respectively. In the cases of the bipolar mode, the contact angles continuously decreased as Va increased and reached 29⬚ for the Žq480, y480. pulsing condition. This result shows that the inverter plasma process-
Fig. 5. Wide scan XPS spectra of LDPE samples: Ža. untreated, Žb᎐d. treated with inverter plasma under the pulsing conditions of Žq480, y0., Žq0,y480., and Žq480, y0., respectively.
268
N. Murakami et al. r Surface and Coatings Technology 136 (2001) 265᎐268
Plasma properties, such as plasma density, depend on the pulsing conditions. Thus, the processing condition, in particular, the processing speed, is not the same for the different pulsing conditions. In fact, the experimental plots in Fig. 4 show a little non-monotonically decreasing behavior. However, because every plasma exposure was performed until the surface reaction was saturated, most of the differences on the treated sample surface must arise, not from the reaction speed, but the reaction mechanism of the hydrophile process.
4. Conclusion
Fig. 6. Narrow scan XPS spectra around the carbon line ŽC 1s. of LDPE samples: Ža. untreated; Žb᎐d. treated with inverter plasma in the pulsing conditions of Žq480, y0., Žq0, y480., and Žq480, y0., respectively. The full width at half maximum of each line profile is also shown.
alcohol at 1᎐2 eV; ester at 1᎐3 eV; ketone at 2᎐3 eV; aldehyde at 2᎐3 eV; and carboxylic at 3᎐4 eV from the C᎐C component. The narrow scan of the same XPS spectra around the carbon line ŽC 1s, 285 eV. is shown in Fig. 6. The full widths at half maximum of the carbon line for the spectra Ža᎐d. in Fig. 6 are 1.1, 1.6, 1.3 and 1.9 ŽeV., respectively. It can clearly be seen that the amount of some oxygen-containing species incorporated onto the surface carbons become bigger in the order: Žq0, y480., Žq480, y0., Žq480, y480. pulsing conditions. Moreover, a strong presence of other lines, which are not yet specified, is also observed in spectrum Žd. for the Žq480, y480. pulsing condition. Generally speaking, polymer surfaces treated with argon glow plasmas have hydrophilic species Ž ᎐OH and ᎐COOH, etc.. introduced to the surface. When positive ions, which have a large momentum compared to that of electron came into collision with the sample surface, more C᎐H combinations are cut off and hydrophilic processing is accomplished more effectively. In the bipolar case Žq480, y480., both electrons and positive ions collided with the sample surface by turns and the hydrophile process was much more effective.
In this work, we have presented results on the hydrophile process using an inverter discharge system and the first correlation of the contact angle with the pulsing conditions. In particular, we have shown that a positive polarity of the voltage applied to the counter electrode is much more effective for hydrophile processing than a negative one. It also seems that a cooperation effect between ions and electrons exists in this surface process, which may be important for a further understanding of a hydrophile process. References w1x J.M. Burksarand, J. Vac. Sci. Technol. 15 Ž1978. 223᎐226. w2x W.L. Wade Jr., R.J. Mammone, M. Binder, J. Appl. Polym. Sci. 43 Ž1991. 1589᎐1591. w3x R.K. Wells, J.P.S. Badyal, I.W. Drummond, K.S. Robinson, F.J. Street, J. Adhes. Sci. Technol. 7 Ž1993. 1129᎐1137. w4x H. Guezenoc, Y. Segui, K. Asfardjani, S. Thery, J. Adhes. Sci. Technol. 7 Ž1993. 953᎐965. w5x D.T. Clark, A. Dilks, J. Polym. Sci, Polym. Chem. Ed. 15 Ž1977. 15᎐30. w6x F. Denes, R.A. Young, M. Sarmadi, J. Photopolym. Sci. 10 Ž1997. 91᎐112. w7x L.J. Gerenser, J. Adhes. Sci. Technol. 7 Ž1993. 1019᎐1040. w8x E. Occhiello, M. Morra, F. Garbassi, D. Johnson, P. Humphrey, Appl. Surf. Sci. 47 Ž1991. 235᎐242. w9x S. Sugimoto, M. Kiuchi, S. Takechi, K. Tanaka, S. Goto, Proc. PBII-99, to appear in Surf. Coat. Technol. w10x M. Kiuchi, K. Tanaka, S. Takechi, S. Sugimoto, S. Goto, Proc. PBII-99, to appear in Surf. Coat. Technol. w11x J.G.A. Terlingen, H.F.C. Geritsen, J. Feijen, A.S. Hoffman, J. Appl. Polym. Sci. 57 Ž1995. 969᎐982. w12x Y. Ikada, T. Matsunage, M. Suzuki, Nippon Kagaku Kaishi 1985 Ž1985. 1079᎐1086.