- Email: [email protected]
Surface modification of PET membrane by ion implantation
ARTICLE IN PRESS
Vacuum 81 (2007) 1348–1351 www.elsevier.com/locate/vacuum
Surface modification of PET membrane by ion implantation Marcin Drabika,, Kazimierz Dworeckia, Roman Tan´czykb, S"awomir Wa˛ sika, Jerzy Z˙ ukc Institute of Physics, S´wi˛etokrzyska Academy, S´wi˛etokrzyska 15, 25-406 Kielce, Poland b Heavy Ion Laboratory, Warsaw University, Pasteura 5A, 02-093 Warsaw, Poland c Institute of Physics, Maria Curie-Sk!odowska University, Pl. M. Curie-Sk!odowskiej 1, 20-031 Lublin, Poland a
Abstract Semicrystalline poly(ethylene terephtalate) (PET) foils were irradiated with N5+, O7+ and C3+ ions. Ions beams of 50 keV N5+, 70 keV O7+ and 30 keV C3+ were produced from the ECR ion source. The induced effects and wettability of ion-implanted membranes were investigated by means of the Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and by the contactangle methods. FTIR measurements of the virgin and irradiated samples show the scission processes of main chains at the ethylene glycol residue. Various degradation processes known from photochemical degradation were also observed. The AFM observation revealed that the surface topography changes after irradiation. The contact-angle measurements showed that the PET membranes became significantly more hydrophilic after the ion irradiation. r 2007 Elsevier Ltd. All rights reserved. Keywords: Membrane; Ion implantation; Atomic force microscopy; Contact angle; Fourier transform infrared spectroscopy; Wettability
1. Introduction Polymer materials with improved mechanical, optical or electrical properties have been widely used in a variety of industrial applications. However, their use is sometimes limited by undesired properties of the surface, contrary to very useful characteristics of the bulk, such as low weight, chemical inertness and high impact resistance. Therefore, it is interesting to modify the surface in a controlled manner to enhance wettability, printability, adhesion with other materials or with biological components, compatibility (as in the production of material blends using two immiscible polymers), etc. [1–4]. Ion irradiation is an established tool for modifying the chemical structure and physical properties of the polymers [5–8]. The ion implantation changes chemical structure and physical properties of the polymers, such as adhesion, friction, wetting, swelling and biological compatibility. The nature of these changes depends on the properties of the polymer, such as composition and molecular weight and on the mass and energy of the incident ions, as well as on the conditions of irradiation. The ion beam irradiation Corresponding author. Fax: +48 41 349 64 43.
E-mail address: [email protected] (M. Drabik). 0042-207X/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2007.01.044
technique has proven more effective in modifying polymer than other particle beam irradiation techniques because of its higher cross section for ionisation and larger linear energy transfer [6]. In this paper, we report on the results of the investigation of the poly(ethylene terephtalate) (PET) films irradiated with N5+, O7+ and C3+ ions having the energy 10 keV/q and the fluence up to 1015 ions/cm2. Three characterisation methods, i.e. the Fourier transform infrared spectroscopy (FTIR), the atomic force microscopy (AFM) and the contact-angle measurement were investigated thoroughly to characterise virgin and implanted films. 2. Experimental procedures The PET membranes with the thickness of 12 mm and the area of 2 cm2 were irradiated with a variety of N5+, O7+ ions with the energy of 10 keV/q and the fluence up to 1 1015 ions/cm2, with a C3+ ions with the energy of 10 keV/q and the fluence up to 1.2 1016 ions/cm2, 6.01 1016 and 2.98 1015 ions/cm2. The irradiation was performed on the ECR ion source at Heavy Ion Laboratory of Warsaw University, Poland. The ECR source is combined with the U-200P cyclotron system.
ARTICLE IN PRESS M. Drabik et al. / Vacuum 81 (2007) 1348–1351
In these experiments, the PET polymer samples were irradiated under vacuum at room temperature. The beam current densities were limited below 30 nA/cm2 to avoid any macroscopic heating of the sample. Theoretical calculations of ion ranges and absorbed dose were carried out using the SRIM-2003.20 code [9]. Simulation showed that the projected ranges of N5+, O7+ and C3+ ions in the polymer in question were 166.8, 214.3 and 121.2 nm, respectively. The irradiated samples as well as unirradiated PET foils were studied by different techniques: (i) FTIR, (ii) AFM and (iii) contactangles method. The chemical state of the polymer foils before and after ion irradiations was analysed by means of FTIR. The FTIR spectra were recorded in the transmission mode using a FTIR Perkin-Elmer Spectrum 2000 spectrometer. The surface morphology was observed by AFM. The AFM investigations of the surface morphology of the samples were carried out with a commercial instrument (Digital Instruments, NanoScope IIIa) equipped with a homebuilt head with a laser deflection detection system. The measurements were performed with a normal spring constant of 0.03 N/m in the contact mode AFM and the scanning range was set at the size of 1.0 mm 1.0 mm in ambient atmosphere.
a
The contact angle of liquid on solid is closely related to surface free energy and this parameter is useful in discussion of hydrophilicity and adhesivity of the sample. The contact angles of water (5 ml) were measured according to a standard method [10] before and after the surface modification at room temperature. Advancing and receding angles were obtained by increasing or decreasing the drop volume. An NRL C.A. Goniometer (A Rame-Hart, Mountain Laikes, NJ, USA) was used to determine the contact angles. 3. Results and discussion FTIR measurements of the irradiated samples show that the modifications of the chemical structure of PET depend on the mass energy and the electronic energy loss averaged over the whole sample volume by the incident ions. Fig. 1(a)–(c) shows the FTIR spectra of PET samples, i.e. the virgin and irradiated with different ions. The FTIR spectra obtained after the irradiation with N5+, O7+ and C3+ ions show similar results, i.e. an overall decrease of the intensity of typical bands of the virgin PET. We observed the changes of absorption bands for the
b Transmission (Arbitrary Units)
Transmission (Arbitrary Units) 4000
1349
3000
2000
1000
4000
3000
ν [1/cm]
2000
1000
ν [1/cm]
Transmission (Arbitrary Units)
c
4000
3000
2000
1000
ν [1/cm] Fig. 1. FTIR spectra of PET membranes, virgin and irradiated with: (a) O7+ with the fluence F ¼ 1 1015 ions/cm2, (b) N5+ with the fluence F ¼ 1 1015 ions/cm2 and (c) C3+ with the fluence F ¼ 6.01 1016 ions/cm2.
ARTICLE IN PRESS M. Drabik et al. / Vacuum 81 (2007) 1348–1351
1350
a
0
c
0
1µm
0 1µm 1µm
0 1µm
b
1µm
0 1µm
0
d
1µm
0 1µm
0
Fig. 2. AFM topographic images of the PET samples: (a) virgin, (b) irradiated with C3+ ions, (c) irradiated with O7+ ions and (d) irradiated with N5+ ions. The scan size is 1.0 mm 1.0 mm.
methylene group in 3751–3245, 1624–1578 and 664–506 cm1 regions [11,12]. The changes of these spectra occurred in the 1740–1660 and 730–631 cm1 regions [12]. The IR spectra of PET samples irradiated with N5+, O7+ and C3+ ions show that this polymer was damaged by the energy deposited by ions in the samples. This energy could be used for many processes, such as amorphization of the crystalline fraction of the polymer, scission of the chains and oxidation [11,13–16]. The modifications in absorption are found to be in agreement with the change of PET sample in colour, which varies from transparent for the pristine membrane to dark brown for the irradiated one. More information of the chemical modification of PET was obtained by means of AFM measurements. Fig. 2(a)–(d) shows the surface nano-morphology of the virgin and irradiated PET membranes with O7+, N5+ and C3+ ions at the fluences 1015 ions/cm2. The figures show that after ion irradiation the polymer surface reorganises in thin peaks separated by free space. The cross-section of each AFM image was analysed in terms of surface average roughness (Ra). The measured roughness para-
Table 1 Roughness parameters: Ra, RRMS Samples
Virgin O7+ N5+ C3+ C3+ C3+
Fluence (ions/cm2) — 1 1015 1 1015 1.20 1016 6.01 1016 2.98 1015
Roughness data Ra (nm)
RRMS (nm)
0.504 0.339 0.334 0.204 0.228 0.240
0.753 0.440 0.826 0.311 0.288 0.256
meters: the average roughness (Ra) and the root mean squares roughness (RRMS) are shown in Table 1. Our results indicate that the surface nano-morphology of PET membranes was significantly affected by ion beam irradiation and the surface roughness decreases after irradiation. The modifications of the PET foils were characterised by means of contact-angle measurement with water drops. The mean values of contact angle are presented in Table 2.
ARTICLE IN PRESS M. Drabik et al. / Vacuum 81 (2007) 1348–1351
1351
Table 2 Contact-angle measurements of water drops obtained for the virgin and implanted samples with O7+, N5+ and C3+ ions Samples
Virgin O7+ N5+ C3+
Fluence (ions/cm2)
— 1 1015 1 1015 2.98 1015
Advancing angle
Receding angle
Hysteresis DY ¼ Yadv–Yrec
Yadv
Sd
Yrec
Sd
85.4 75.8 69.8 78.3
1.9 2.6 4.1 3.1
67.3 50.2 45.9 55.4
4.3 4.7 7.5 5.7
The contact-angle measurements with water drops reveal, as expected, a very high hydrophobicity of the virgin sample. The PET sample surfaces became more hydrophilic after their irradiation with ions. The increase of the hydrophilicity of the surface after ion irradiation in this case indicates that a change in the chemical composition of the surface takes place. In general, the hysteresis in the contact angles DQ (DQ ¼ QadvQrec) gives some indication about the surface roughness and composition [10]. 4. Conclusions The changes of the implanted PET samples were examined using FTIR, AFM and contact-angle methods. Based on the FTIR measurements, the ion irradiated PET membranes exhibit changes in chemical structure (chain scissions and structure degradations). The AFM images indicate decrease of the surface roughness of the implanted foils. AFM observations also reveal that an increase in the dose of C3+ ions decreases surface roughness. The contact-angle measurements show that the PET membranes become significantly more hydrophilic after the ion irradiation. We intend to carry out thorough study concerning diffusional permeability of these membranes in the future.
18.1 25.6 23.9 22.9
References [1] Park JW, Sohn CW, Choi BH. Curr Appl Phys 2006;6:188. [2] Ektessabi AM, Sano T. Rev Sci Technol 2000;71:1012. [3] Spohr R. In: Bethe K, editor. Ion tracks and microtechnology, basic principles and applications. Braunschweig: Vieweg; 1990. [4] Ektessabi AM, Yamaguchi K. Thin Solid Films 2000;377–378:793. [5] Kryszewski M. Semiconducting polymers. Warsaw: Polish Scientific Publishers; 1980. [6] Toth A, Bell T, Bertoti I, Mohai I, Zelei B. Nucl Instrum Methods B 1999;148:1131. [7] Zhang J, Yu X, Li H, Liu X. Appl Surf Sci 2002;185:255. [8] Chico B, Martinez L, Perez FJ. Appl Surf Sci 2005;243:409. [9] Ziegler JF, Biersack JP, Littmark U. The stopping and range of ions in solid. New York: Pergamon Press; 1985 http://www.srim.org. [10] Noda I. Contact angle, Adhesian, The Netherlands, 1993. [11] Steckenreiter T, Balazat E, Fuess H, Trautmann C. Nucl Instrum Methods B 1997;131:159. [12] Silverstein RM, Bassler GC, Morill TC. Spectrometric identification of organic compounds. New York: Wiley; 1990 [chapter 3]. [13] Ciesla K, Starosta W. Nucl Instrum Methods B 1995;105:115. [14] Turos A, Jagielski J, Pia˛ tkowska A, Bielin´ski D, S´lusarski L, Madi NK. Vacuum 2003;70:201. [15] Dworecki K, Drabik M, Hasegawa T, Wa˛ sik S. Nucl Instrum Methods B 2004;255:483. [16] Takahashi S, Yoshida M, Asano M, Notoni M, Nakagawa T. Nucl Instrum Methods B 2004;217:435.
Vacuum 81 (2007) 1348–1351 www.elsevier.com/locate/vacuum
Surface modification of PET membrane by ion implantation Marcin Drabika,, Kazimierz Dworeckia, Roman Tan´czykb, S"awomir Wa˛ sika, Jerzy Z˙ ukc Institute of Physics, S´wi˛etokrzyska Academy, S´wi˛etokrzyska 15, 25-406 Kielce, Poland b Heavy Ion Laboratory, Warsaw University, Pasteura 5A, 02-093 Warsaw, Poland c Institute of Physics, Maria Curie-Sk!odowska University, Pl. M. Curie-Sk!odowskiej 1, 20-031 Lublin, Poland a
Abstract Semicrystalline poly(ethylene terephtalate) (PET) foils were irradiated with N5+, O7+ and C3+ ions. Ions beams of 50 keV N5+, 70 keV O7+ and 30 keV C3+ were produced from the ECR ion source. The induced effects and wettability of ion-implanted membranes were investigated by means of the Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and by the contactangle methods. FTIR measurements of the virgin and irradiated samples show the scission processes of main chains at the ethylene glycol residue. Various degradation processes known from photochemical degradation were also observed. The AFM observation revealed that the surface topography changes after irradiation. The contact-angle measurements showed that the PET membranes became significantly more hydrophilic after the ion irradiation. r 2007 Elsevier Ltd. All rights reserved. Keywords: Membrane; Ion implantation; Atomic force microscopy; Contact angle; Fourier transform infrared spectroscopy; Wettability
1. Introduction Polymer materials with improved mechanical, optical or electrical properties have been widely used in a variety of industrial applications. However, their use is sometimes limited by undesired properties of the surface, contrary to very useful characteristics of the bulk, such as low weight, chemical inertness and high impact resistance. Therefore, it is interesting to modify the surface in a controlled manner to enhance wettability, printability, adhesion with other materials or with biological components, compatibility (as in the production of material blends using two immiscible polymers), etc. [1–4]. Ion irradiation is an established tool for modifying the chemical structure and physical properties of the polymers [5–8]. The ion implantation changes chemical structure and physical properties of the polymers, such as adhesion, friction, wetting, swelling and biological compatibility. The nature of these changes depends on the properties of the polymer, such as composition and molecular weight and on the mass and energy of the incident ions, as well as on the conditions of irradiation. The ion beam irradiation Corresponding author. Fax: +48 41 349 64 43.
E-mail address: [email protected] (M. Drabik). 0042-207X/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2007.01.044
technique has proven more effective in modifying polymer than other particle beam irradiation techniques because of its higher cross section for ionisation and larger linear energy transfer [6]. In this paper, we report on the results of the investigation of the poly(ethylene terephtalate) (PET) films irradiated with N5+, O7+ and C3+ ions having the energy 10 keV/q and the fluence up to 1015 ions/cm2. Three characterisation methods, i.e. the Fourier transform infrared spectroscopy (FTIR), the atomic force microscopy (AFM) and the contact-angle measurement were investigated thoroughly to characterise virgin and implanted films. 2. Experimental procedures The PET membranes with the thickness of 12 mm and the area of 2 cm2 were irradiated with a variety of N5+, O7+ ions with the energy of 10 keV/q and the fluence up to 1 1015 ions/cm2, with a C3+ ions with the energy of 10 keV/q and the fluence up to 1.2 1016 ions/cm2, 6.01 1016 and 2.98 1015 ions/cm2. The irradiation was performed on the ECR ion source at Heavy Ion Laboratory of Warsaw University, Poland. The ECR source is combined with the U-200P cyclotron system.
ARTICLE IN PRESS M. Drabik et al. / Vacuum 81 (2007) 1348–1351
In these experiments, the PET polymer samples were irradiated under vacuum at room temperature. The beam current densities were limited below 30 nA/cm2 to avoid any macroscopic heating of the sample. Theoretical calculations of ion ranges and absorbed dose were carried out using the SRIM-2003.20 code [9]. Simulation showed that the projected ranges of N5+, O7+ and C3+ ions in the polymer in question were 166.8, 214.3 and 121.2 nm, respectively. The irradiated samples as well as unirradiated PET foils were studied by different techniques: (i) FTIR, (ii) AFM and (iii) contactangles method. The chemical state of the polymer foils before and after ion irradiations was analysed by means of FTIR. The FTIR spectra were recorded in the transmission mode using a FTIR Perkin-Elmer Spectrum 2000 spectrometer. The surface morphology was observed by AFM. The AFM investigations of the surface morphology of the samples were carried out with a commercial instrument (Digital Instruments, NanoScope IIIa) equipped with a homebuilt head with a laser deflection detection system. The measurements were performed with a normal spring constant of 0.03 N/m in the contact mode AFM and the scanning range was set at the size of 1.0 mm 1.0 mm in ambient atmosphere.
a
The contact angle of liquid on solid is closely related to surface free energy and this parameter is useful in discussion of hydrophilicity and adhesivity of the sample. The contact angles of water (5 ml) were measured according to a standard method [10] before and after the surface modification at room temperature. Advancing and receding angles were obtained by increasing or decreasing the drop volume. An NRL C.A. Goniometer (A Rame-Hart, Mountain Laikes, NJ, USA) was used to determine the contact angles. 3. Results and discussion FTIR measurements of the irradiated samples show that the modifications of the chemical structure of PET depend on the mass energy and the electronic energy loss averaged over the whole sample volume by the incident ions. Fig. 1(a)–(c) shows the FTIR spectra of PET samples, i.e. the virgin and irradiated with different ions. The FTIR spectra obtained after the irradiation with N5+, O7+ and C3+ ions show similar results, i.e. an overall decrease of the intensity of typical bands of the virgin PET. We observed the changes of absorption bands for the
b Transmission (Arbitrary Units)
Transmission (Arbitrary Units) 4000
1349
3000
2000
1000
4000
3000
ν [1/cm]
2000
1000
ν [1/cm]
Transmission (Arbitrary Units)
c
4000
3000
2000
1000
ν [1/cm] Fig. 1. FTIR spectra of PET membranes, virgin and irradiated with: (a) O7+ with the fluence F ¼ 1 1015 ions/cm2, (b) N5+ with the fluence F ¼ 1 1015 ions/cm2 and (c) C3+ with the fluence F ¼ 6.01 1016 ions/cm2.
ARTICLE IN PRESS M. Drabik et al. / Vacuum 81 (2007) 1348–1351
1350
a
0
c
0
1µm
0 1µm 1µm
0 1µm
b
1µm
0 1µm
0
d
1µm
0 1µm
0
Fig. 2. AFM topographic images of the PET samples: (a) virgin, (b) irradiated with C3+ ions, (c) irradiated with O7+ ions and (d) irradiated with N5+ ions. The scan size is 1.0 mm 1.0 mm.
methylene group in 3751–3245, 1624–1578 and 664–506 cm1 regions [11,12]. The changes of these spectra occurred in the 1740–1660 and 730–631 cm1 regions [12]. The IR spectra of PET samples irradiated with N5+, O7+ and C3+ ions show that this polymer was damaged by the energy deposited by ions in the samples. This energy could be used for many processes, such as amorphization of the crystalline fraction of the polymer, scission of the chains and oxidation [11,13–16]. The modifications in absorption are found to be in agreement with the change of PET sample in colour, which varies from transparent for the pristine membrane to dark brown for the irradiated one. More information of the chemical modification of PET was obtained by means of AFM measurements. Fig. 2(a)–(d) shows the surface nano-morphology of the virgin and irradiated PET membranes with O7+, N5+ and C3+ ions at the fluences 1015 ions/cm2. The figures show that after ion irradiation the polymer surface reorganises in thin peaks separated by free space. The cross-section of each AFM image was analysed in terms of surface average roughness (Ra). The measured roughness para-
Table 1 Roughness parameters: Ra, RRMS Samples
Virgin O7+ N5+ C3+ C3+ C3+
Fluence (ions/cm2) — 1 1015 1 1015 1.20 1016 6.01 1016 2.98 1015
Roughness data Ra (nm)
RRMS (nm)
0.504 0.339 0.334 0.204 0.228 0.240
0.753 0.440 0.826 0.311 0.288 0.256
meters: the average roughness (Ra) and the root mean squares roughness (RRMS) are shown in Table 1. Our results indicate that the surface nano-morphology of PET membranes was significantly affected by ion beam irradiation and the surface roughness decreases after irradiation. The modifications of the PET foils were characterised by means of contact-angle measurement with water drops. The mean values of contact angle are presented in Table 2.
ARTICLE IN PRESS M. Drabik et al. / Vacuum 81 (2007) 1348–1351
1351
Table 2 Contact-angle measurements of water drops obtained for the virgin and implanted samples with O7+, N5+ and C3+ ions Samples
Virgin O7+ N5+ C3+
Fluence (ions/cm2)
— 1 1015 1 1015 2.98 1015
Advancing angle
Receding angle
Hysteresis DY ¼ Yadv–Yrec
Yadv
Sd
Yrec
Sd
85.4 75.8 69.8 78.3
1.9 2.6 4.1 3.1
67.3 50.2 45.9 55.4
4.3 4.7 7.5 5.7
The contact-angle measurements with water drops reveal, as expected, a very high hydrophobicity of the virgin sample. The PET sample surfaces became more hydrophilic after their irradiation with ions. The increase of the hydrophilicity of the surface after ion irradiation in this case indicates that a change in the chemical composition of the surface takes place. In general, the hysteresis in the contact angles DQ (DQ ¼ QadvQrec) gives some indication about the surface roughness and composition [10]. 4. Conclusions The changes of the implanted PET samples were examined using FTIR, AFM and contact-angle methods. Based on the FTIR measurements, the ion irradiated PET membranes exhibit changes in chemical structure (chain scissions and structure degradations). The AFM images indicate decrease of the surface roughness of the implanted foils. AFM observations also reveal that an increase in the dose of C3+ ions decreases surface roughness. The contact-angle measurements show that the PET membranes become significantly more hydrophilic after the ion irradiation. We intend to carry out thorough study concerning diffusional permeability of these membranes in the future.
18.1 25.6 23.9 22.9
References [1] Park JW, Sohn CW, Choi BH. Curr Appl Phys 2006;6:188. [2] Ektessabi AM, Sano T. Rev Sci Technol 2000;71:1012. [3] Spohr R. In: Bethe K, editor. Ion tracks and microtechnology, basic principles and applications. Braunschweig: Vieweg; 1990. [4] Ektessabi AM, Yamaguchi K. Thin Solid Films 2000;377–378:793. [5] Kryszewski M. Semiconducting polymers. Warsaw: Polish Scientific Publishers; 1980. [6] Toth A, Bell T, Bertoti I, Mohai I, Zelei B. Nucl Instrum Methods B 1999;148:1131. [7] Zhang J, Yu X, Li H, Liu X. Appl Surf Sci 2002;185:255. [8] Chico B, Martinez L, Perez FJ. Appl Surf Sci 2005;243:409. [9] Ziegler JF, Biersack JP, Littmark U. The stopping and range of ions in solid. New York: Pergamon Press; 1985 http://www.srim.org. [10] Noda I. Contact angle, Adhesian, The Netherlands, 1993. [11] Steckenreiter T, Balazat E, Fuess H, Trautmann C. Nucl Instrum Methods B 1997;131:159. [12] Silverstein RM, Bassler GC, Morill TC. Spectrometric identification of organic compounds. New York: Wiley; 1990 [chapter 3]. [13] Ciesla K, Starosta W. Nucl Instrum Methods B 1995;105:115. [14] Turos A, Jagielski J, Pia˛ tkowska A, Bielin´ski D, S´lusarski L, Madi NK. Vacuum 2003;70:201. [15] Dworecki K, Drabik M, Hasegawa T, Wa˛ sik S. Nucl Instrum Methods B 2004;255:483. [16] Takahashi S, Yoshida M, Asano M, Notoni M, Nakagawa T. Nucl Instrum Methods B 2004;217:435.