- Email: [email protected]
Aging effects on wettability and structure of ion implanted silicone
354
AGING Yoshiaki
Nuclear
EFFECTS SUZUKI,
ON WElTABILITY Craig SWAPP
Masaya
AND STRUCTURE
and Masahiro
Son>, Corp. 6-7-35. Kitashlncrguwu Shinqmcku,
Instruments
T&w.
and Methods
in Physics
Research
OF ION IMPLANTED
846 (1990) 354-357 North-Holland
SILICONE
KUSAKABE
141 Japan
IWAKI
RIKEA’, HJcrko, Sammu-pref,
351-01, Jupun
The wettability, structure, and chemical states of ion implanted silicone rubbers were investigated in relation to aging in air and were performed at energies of 100 and I50 keV vacuum. H+. He’, C’. N+. O+, Ne-. Na+, NT. 0;. Ar + and K + ion implantations at room temperature. Wettability was investigated by contact angle measurements. which showed that the contact angle of water, immediately after Ion implantation on the specimens. was decreased under high fluence. The minimum value of contact angle depended on the mass of the implanted ion species. The heavy weight ions were more effective than light ions for improving uettability. As time elapsed, the contact angle gradually increased and finally approached the initial value. Specimens subjected to vacuum conditions required a longer aging time to return to the initial value than specimens exposed to ambient room conditions. Results of FT-IR-ATR showed that ion implantation broke original chemical bonds to form nen radicals, and the changes in these chemical bonds and radicals were dependent on the state of preservation of the specimens as the time elapsed. It was concluded that the return to the initial contact angle in atmospheric conditions was due to recombination of slloxane bonds.
1. Introduction Ion implantation is a useful technique for improvement of surface properties such as wear and corrosion resistance for metals [I]. In recent years it has also been applied to surface modification of polymers in order to control electrical properties, surface energies and biocompatibility. It has been demonstrated that the electrical conductivity in implanted polyimide films can be controlled by implantation energy and fluence [2]. Medical grade silicone rubbers modified by Naf implantation cause a change in the amount of plasma proteins which bond to the specimens [3]. Our previous study of wettability showed that ion implantation in silicone caused the contact angle of water to drop from an initial angle of 98.9” to about 50” as the fluence increased [4,5]. In this report. the aging effects on the contact angle of w’ater onto implanted silicone rubber were investigated in relation to the structure and chemical states by FT-IR-ATR and XPS.
2. Experimental Substrates used were silicone rubber sheets, which are medical grade materials produced by Toshiba Silicone Corp. (THE740-8U). H+, He’. Cf, N+. O+. Ne’. Arf and K+ ion implantations were Nat. N:. 0:. performed at energies of 100 and 150 keV at room temperature by using a RIKEN 200 kV low current implanter. The beam current density used was less than 0168-583X/90/$03.50 (North-Holland)
L Elsevier Science Pubhshers
B.V.
2 PA/cm’ to prevent the specimen’s temperature from increasing and the fluence ranged from 1 x 10” to 1 X 10” ions/cm*. Wettability was evaluated by measuring the contact angle of water dropped onto the surfaces of implanted specimens. i.e. the sessile drop method. Depth profiles in ion implanted silicone were investigated by means of X-ray photoelectron spectroscopy (AEI-100) combined with sputter etching using a 3 keV Ar ion beam. Functional group analyses of implanted silicones were carried out by Fourier transform infrared spectroscopy (FTS-lSE/D. Biorad Digilab) combined with attenuated total reflectance (FT-IR-ATR) as described in detail in our previous paper [5].
3. Results and discussion 3. I. Wettuhilig The contact angle of water for C+, N2+. 0;. and silicone decreased as a function of Ar+ implanted fluence at energies of 50 and 100 keV [5]. The contact angle of water for Hi, He’, Nei and Na + implanted specimens exhibited the same tendency as described for and Art implanted specimens. Fig. 1 C+. N,‘, 0: shows the relation between the contact angle, measured immediately after ion implantation, and the mass of the implanted ions at 150 keV with a fluence of 1 x 10” ions/cm’. We found that the decrease in contact angle for implanted specimens is directly proportional to the increase of the mass of the implanted ions.
355
Y.Suzuki ef al. /Aging effects on rhe structure of silicone 1
1lOp
8 tt; look3 ‘0 6 90. E:SOal-
8
S-0
CH3
H+ He+
a 0
:ETl _ $70.
“9 E
’
0 l 0 a
60. SO; 0
10
fc 40
30
20 Mass (amu
Fig. 1. The relationship between contact angle of water and mass of implanted ions. The arrow indicates the initial value for a pristine silicone.
The contact angle of water for implanted specimens were influenced by aging under ambient room conditions. Fig. 2 shows the contact angle of water for specimens implanted with N: , 0; and Ar+ ion at 100 keV with 1 x lOI ions/cm* as a function of aging time. The black square in the figure is the contact angle of water for the 0: ion implanted specimen after 22 h of aging in vacuum. As time elapsed the contact angle gradually increased and finally approached the initial value of 98.9 O. Specimens subjected to vacuum conditions required a longer aging time to return to the initial contact angle than specimens exposed to ambient room conditions. 3.2. Functional group and decomposition IR-ATR
anal_blsesof FT-
Absorbance spectra of ion implanted specimens by FT-IR-ATR were measured in a range of wavenumbers from 680 to 400 cm-’ combined with Ge or KRS-5 prisms [4,5]. Ion implantation decomposed the CH, and Si-0 bonds to form new radicals [5]. In order to estimate the decomposition of siloxane and methyl, the peak intensities of siloxane at 1080 cm-’ and methyl at 1260 cm-’ were divided by that of
0
10
100
)
20
30
Time (hours)
Fig. 2. Atmospheric aging effects on the contact for 0: (o), NC (0) and Ar+ (A) implantation (w) in vacuum conditions.
angle of water in air and 0:
Fig.
50 -0 dlOsO/d1020 %
o-
50
100
d1260Kd1020 ‘4
3. Decomposition ratio of methyl and siloxane at an energy of 150 keV with a fluence of 1 x 10” ions/cm’.
siloxane at 1020 cm-‘, because ion implantation caused little change in the intensity of the peak at 1020 cm-‘. Fig. 3 shows the decomposition ratio of methyl and siloxane. Ne+ ion implantation was the most effect in decomposing SiO and CH, among the ion species used in these experiments. The decomposition ratio of Si-0 and CH, had no relation to the mass of the implanted ion species. 3.3. Evaluation of new radical concentration ATR measurements as a function qf time
lg, FT-IR-
Figs. 4a and b show the intensity ratio of OH (3400 cm-‘). SiH (2120 cm-‘) and > C = 0 (1720 cm-‘) relative to the asymmetric CH stretch vibration (2970 cm-‘), 1 d and 8 d after 100 keV 0: implantation with a fluence of 1 X 10” ions/cm2. and the difference between the sample left in air (A) and in vacuum (V) by means of FT-IR-ATR with Ge (a) and KRS-5 (b) prisms. According to a calculation based on the theory of IR absorbance, using a Ge prism at 2000 cm-’ allows us to assess the radical composition from the specimen surface to a depth of 0.2 pm. A KRS-5 prism at 2000 cm-’ yields the same information to a depth of 0.6 km. As shown in fig. 4a. the intensity ratio of OH increased as a function of time in air and decreased in vacuum. However, the intensity ratio of SiH and > C = 0 decreased both in air and vacuum. As shown in fig. 4b the intensity ratios of OH and > C = 0 increased and that of SiH decreased as a function of time. and there was no difference between air and vacuum. These results indicate that, in air, the intensity ratio of OH increased in the upper surface, and that. in vacuum, it increased in the inner surface layer. The intensity ratio of SiH decreased both in the upper and inner surface layer and that of > C = 0 decreased in the upper surface and increased in the inner surface. The changes of SiH and > C = 0 were not affected by the condition of preservation. Figs. 5a and b show the aging effects on methylene (a) and siloxane bonds (b) 1 d and 8 d after 100 keV 0: implantation with a fluence of 1 x 10” ions/cm*, and the difference between the sample left in VI. POLYMERS
,‘ORGANICS
Y. Suzuki et al. /Aging effects on the structure of srlicone
356
@)O.& )H
1Hz=0
ISiH
‘b)0.3
OH
,rc=o
SiH
I ‘i E O0.E x % \
7
E 0
ho 2 0.2. \ g m L z=. .= ; 0.1
0
go.4 L 2 ‘Z 5 Eo.2
E
0
I A
L
----V
A V Condition
A
V
I
r
0:
I
I-
- -- - -- nl
V
A Conditio:
A
V
after 1 d (0) and 8 d (M), measured by FT-IR-ATR combined with Fig. 4. Aging effects on new radic ,als due to 0; ion implantation Ge (a) and KRS-5 (d) prisms. The sample was left in air (A) and in vacuum (V) after ion implantation.
_~
Control
Fig. 5. Aging
A
~ V
ion implantation, measured effects on methyl (a) and siloxane (b) after 1 d (0) and 8 d (M) 0: combined with a Ge prism. The sample was left in air (A) and in vacuum (V) after ion implantation.
air (A) and in vacuum (V) when evaluated by using a Ge prism. Figs. 5a and b illustrate the intensity ratio of the methyl (1260 cm-‘) and siloxane bond (1080 cm-‘) respectively to that of the asymmetric SiOSi stretch vibration (1020 cm-‘). The intensity ratio of methyl and siloxane bonds increased in air, and there was no significant change in vacuum-treated specimens as a function of time. Air preservation resulted in an increased intensity ratio of the OH radical in the upper surface. Due to increased hydrogen bonding, the wettability should have improved as the specimen aged. However, the contact angle of water increased, as a function of time, to its original value when the specimen was exposed to ambient room conditions. Analysis of FT-IR-ATR data attributes this result to the recombination of SiO as a function of time.
with a fluence of 1 x lOI ions/cm2, 2 d after ion implantation measured by XPS. This shows the difference between the depth profiles of samples left in air
0
100
200
Etching
3.4. Depth profiles for air us vacuum preservation Fig. 6 shows the depth profiles of C, 0 and Si in the upper surface for 100 keV 0: implanted silicone rubber
by FT-IR-ATR
300
400
500
timetmin)
Fig. 6. Depth profile of C, 0 and Si for 100 keV 0: ion implanted silicone rubber after 2 d, measured by XPS. The sample was left in air (full line) and in vacuum (dashed line) after ion implantation.
357
Y. Suzuki et al. / Aging effects an the structure of silicone
and in vacuum respectively, after ion implantation. The concentration of oxygen was greater in air than in vacuum. These results indicate that oxidation occurred in ambient room conditions.
chemical bonds to form new radicals and, as time elapsed, siloxane bonds were recombined under air conditions. It is concluded that the decrease in wettability was mainly caused by recombination of the siloxane bonds.
4. Summary References An experimental study has been made of the aging effects on the structure and chemical states of ion-implanted silicone rubbers in relation to wettability. The contact angle of water immediately after ion implantation decreased. and the decrease is directly proportional to the mass of the implanted ion species. As time elapsed, the contact angle of water gradually increased to approach its initial value. This phenomenon depended on the conditions of preservation. The results of FT-IRATR showed that ion implantation broke original
PI M. Iwaki, CRC Critical Reviews in Solid State and Material Science, vol. 15. issue 5 (1989) p. 473. and S. Pignataro, Nucl. Instr. and Meth. B39 (1989) 792. M. Iwake, K. Kusakabe. H. [31 Y. Suzuki, M. Kusakabe, Akiba and S. Sato, Mater. Res. Sot. Symp. 110 (1989) 669. [41 Y. Suzuki, M. Kusakabe. M. lwaki and M. Suzuki, Mater. Res. Sot. Symp., in press. ISI Y. Suzuki. M. Kusakabe, M. lwaki and M. Suzuki. Nucl. Instr. and Meth. B32 (1988) 120.
PI G. Marletta
VI. POLYMERS
/ ORGANICS
AGING Yoshiaki
Nuclear
EFFECTS SUZUKI,
ON WElTABILITY Craig SWAPP
Masaya
AND STRUCTURE
and Masahiro
Son>, Corp. 6-7-35. Kitashlncrguwu Shinqmcku,
Instruments
T&w.
and Methods
in Physics
Research
OF ION IMPLANTED
846 (1990) 354-357 North-Holland
SILICONE
KUSAKABE
141 Japan
IWAKI
RIKEA’, HJcrko, Sammu-pref,
351-01, Jupun
The wettability, structure, and chemical states of ion implanted silicone rubbers were investigated in relation to aging in air and were performed at energies of 100 and I50 keV vacuum. H+. He’, C’. N+. O+, Ne-. Na+, NT. 0;. Ar + and K + ion implantations at room temperature. Wettability was investigated by contact angle measurements. which showed that the contact angle of water, immediately after Ion implantation on the specimens. was decreased under high fluence. The minimum value of contact angle depended on the mass of the implanted ion species. The heavy weight ions were more effective than light ions for improving uettability. As time elapsed, the contact angle gradually increased and finally approached the initial value. Specimens subjected to vacuum conditions required a longer aging time to return to the initial value than specimens exposed to ambient room conditions. Results of FT-IR-ATR showed that ion implantation broke original chemical bonds to form nen radicals, and the changes in these chemical bonds and radicals were dependent on the state of preservation of the specimens as the time elapsed. It was concluded that the return to the initial contact angle in atmospheric conditions was due to recombination of slloxane bonds.
1. Introduction Ion implantation is a useful technique for improvement of surface properties such as wear and corrosion resistance for metals [I]. In recent years it has also been applied to surface modification of polymers in order to control electrical properties, surface energies and biocompatibility. It has been demonstrated that the electrical conductivity in implanted polyimide films can be controlled by implantation energy and fluence [2]. Medical grade silicone rubbers modified by Naf implantation cause a change in the amount of plasma proteins which bond to the specimens [3]. Our previous study of wettability showed that ion implantation in silicone caused the contact angle of water to drop from an initial angle of 98.9” to about 50” as the fluence increased [4,5]. In this report. the aging effects on the contact angle of w’ater onto implanted silicone rubber were investigated in relation to the structure and chemical states by FT-IR-ATR and XPS.
2. Experimental Substrates used were silicone rubber sheets, which are medical grade materials produced by Toshiba Silicone Corp. (THE740-8U). H+, He’. Cf, N+. O+. Ne’. Arf and K+ ion implantations were Nat. N:. 0:. performed at energies of 100 and 150 keV at room temperature by using a RIKEN 200 kV low current implanter. The beam current density used was less than 0168-583X/90/$03.50 (North-Holland)
L Elsevier Science Pubhshers
B.V.
2 PA/cm’ to prevent the specimen’s temperature from increasing and the fluence ranged from 1 x 10” to 1 X 10” ions/cm*. Wettability was evaluated by measuring the contact angle of water dropped onto the surfaces of implanted specimens. i.e. the sessile drop method. Depth profiles in ion implanted silicone were investigated by means of X-ray photoelectron spectroscopy (AEI-100) combined with sputter etching using a 3 keV Ar ion beam. Functional group analyses of implanted silicones were carried out by Fourier transform infrared spectroscopy (FTS-lSE/D. Biorad Digilab) combined with attenuated total reflectance (FT-IR-ATR) as described in detail in our previous paper [5].
3. Results and discussion 3. I. Wettuhilig The contact angle of water for C+, N2+. 0;. and silicone decreased as a function of Ar+ implanted fluence at energies of 50 and 100 keV [5]. The contact angle of water for Hi, He’, Nei and Na + implanted specimens exhibited the same tendency as described for and Art implanted specimens. Fig. 1 C+. N,‘, 0: shows the relation between the contact angle, measured immediately after ion implantation, and the mass of the implanted ions at 150 keV with a fluence of 1 x 10” ions/cm’. We found that the decrease in contact angle for implanted specimens is directly proportional to the increase of the mass of the implanted ions.
355
Y.Suzuki ef al. /Aging effects on rhe structure of silicone 1
1lOp
8 tt; look3 ‘0 6 90. E:SOal-
8
S-0
CH3
H+ He+
a 0
:ETl _ $70.
“9 E
’
0 l 0 a
60. SO; 0
10
fc 40
30
20 Mass (amu
Fig. 1. The relationship between contact angle of water and mass of implanted ions. The arrow indicates the initial value for a pristine silicone.
The contact angle of water for implanted specimens were influenced by aging under ambient room conditions. Fig. 2 shows the contact angle of water for specimens implanted with N: , 0; and Ar+ ion at 100 keV with 1 x lOI ions/cm* as a function of aging time. The black square in the figure is the contact angle of water for the 0: ion implanted specimen after 22 h of aging in vacuum. As time elapsed the contact angle gradually increased and finally approached the initial value of 98.9 O. Specimens subjected to vacuum conditions required a longer aging time to return to the initial contact angle than specimens exposed to ambient room conditions. 3.2. Functional group and decomposition IR-ATR
anal_blsesof FT-
Absorbance spectra of ion implanted specimens by FT-IR-ATR were measured in a range of wavenumbers from 680 to 400 cm-’ combined with Ge or KRS-5 prisms [4,5]. Ion implantation decomposed the CH, and Si-0 bonds to form new radicals [5]. In order to estimate the decomposition of siloxane and methyl, the peak intensities of siloxane at 1080 cm-’ and methyl at 1260 cm-’ were divided by that of
0
10
100
)
20
30
Time (hours)
Fig. 2. Atmospheric aging effects on the contact for 0: (o), NC (0) and Ar+ (A) implantation (w) in vacuum conditions.
angle of water in air and 0:
Fig.
50 -0 dlOsO/d1020 %
o-
50
100
d1260Kd1020 ‘4
3. Decomposition ratio of methyl and siloxane at an energy of 150 keV with a fluence of 1 x 10” ions/cm’.
siloxane at 1020 cm-‘, because ion implantation caused little change in the intensity of the peak at 1020 cm-‘. Fig. 3 shows the decomposition ratio of methyl and siloxane. Ne+ ion implantation was the most effect in decomposing SiO and CH, among the ion species used in these experiments. The decomposition ratio of Si-0 and CH, had no relation to the mass of the implanted ion species. 3.3. Evaluation of new radical concentration ATR measurements as a function qf time
lg, FT-IR-
Figs. 4a and b show the intensity ratio of OH (3400 cm-‘). SiH (2120 cm-‘) and > C = 0 (1720 cm-‘) relative to the asymmetric CH stretch vibration (2970 cm-‘), 1 d and 8 d after 100 keV 0: implantation with a fluence of 1 X 10” ions/cm2. and the difference between the sample left in air (A) and in vacuum (V) by means of FT-IR-ATR with Ge (a) and KRS-5 (b) prisms. According to a calculation based on the theory of IR absorbance, using a Ge prism at 2000 cm-’ allows us to assess the radical composition from the specimen surface to a depth of 0.2 pm. A KRS-5 prism at 2000 cm-’ yields the same information to a depth of 0.6 km. As shown in fig. 4a. the intensity ratio of OH increased as a function of time in air and decreased in vacuum. However, the intensity ratio of SiH and > C = 0 decreased both in air and vacuum. As shown in fig. 4b the intensity ratios of OH and > C = 0 increased and that of SiH decreased as a function of time. and there was no difference between air and vacuum. These results indicate that, in air, the intensity ratio of OH increased in the upper surface, and that. in vacuum, it increased in the inner surface layer. The intensity ratio of SiH decreased both in the upper and inner surface layer and that of > C = 0 decreased in the upper surface and increased in the inner surface. The changes of SiH and > C = 0 were not affected by the condition of preservation. Figs. 5a and b show the aging effects on methylene (a) and siloxane bonds (b) 1 d and 8 d after 100 keV 0: implantation with a fluence of 1 x 10” ions/cm*, and the difference between the sample left in VI. POLYMERS
,‘ORGANICS
Y. Suzuki et al. /Aging effects on the structure of srlicone
356
@)O.& )H
1Hz=0
ISiH
‘b)0.3
OH
,rc=o
SiH
I ‘i E O0.E x % \
7
E 0
ho 2 0.2. \ g m L z=. .= ; 0.1
0
go.4 L 2 ‘Z 5 Eo.2
E
0
I A
L
----V
A V Condition
A
V
I
r
0:
I
I-
- -- - -- nl
V
A Conditio:
A
V
after 1 d (0) and 8 d (M), measured by FT-IR-ATR combined with Fig. 4. Aging effects on new radic ,als due to 0; ion implantation Ge (a) and KRS-5 (d) prisms. The sample was left in air (A) and in vacuum (V) after ion implantation.
_~
Control
Fig. 5. Aging
A
~ V
ion implantation, measured effects on methyl (a) and siloxane (b) after 1 d (0) and 8 d (M) 0: combined with a Ge prism. The sample was left in air (A) and in vacuum (V) after ion implantation.
air (A) and in vacuum (V) when evaluated by using a Ge prism. Figs. 5a and b illustrate the intensity ratio of the methyl (1260 cm-‘) and siloxane bond (1080 cm-‘) respectively to that of the asymmetric SiOSi stretch vibration (1020 cm-‘). The intensity ratio of methyl and siloxane bonds increased in air, and there was no significant change in vacuum-treated specimens as a function of time. Air preservation resulted in an increased intensity ratio of the OH radical in the upper surface. Due to increased hydrogen bonding, the wettability should have improved as the specimen aged. However, the contact angle of water increased, as a function of time, to its original value when the specimen was exposed to ambient room conditions. Analysis of FT-IR-ATR data attributes this result to the recombination of SiO as a function of time.
with a fluence of 1 x lOI ions/cm2, 2 d after ion implantation measured by XPS. This shows the difference between the depth profiles of samples left in air
0
100
200
Etching
3.4. Depth profiles for air us vacuum preservation Fig. 6 shows the depth profiles of C, 0 and Si in the upper surface for 100 keV 0: implanted silicone rubber
by FT-IR-ATR
300
400
500
timetmin)
Fig. 6. Depth profile of C, 0 and Si for 100 keV 0: ion implanted silicone rubber after 2 d, measured by XPS. The sample was left in air (full line) and in vacuum (dashed line) after ion implantation.
357
Y. Suzuki et al. / Aging effects an the structure of silicone
and in vacuum respectively, after ion implantation. The concentration of oxygen was greater in air than in vacuum. These results indicate that oxidation occurred in ambient room conditions.
chemical bonds to form new radicals and, as time elapsed, siloxane bonds were recombined under air conditions. It is concluded that the decrease in wettability was mainly caused by recombination of the siloxane bonds.
4. Summary References An experimental study has been made of the aging effects on the structure and chemical states of ion-implanted silicone rubbers in relation to wettability. The contact angle of water immediately after ion implantation decreased. and the decrease is directly proportional to the mass of the implanted ion species. As time elapsed, the contact angle of water gradually increased to approach its initial value. This phenomenon depended on the conditions of preservation. The results of FT-IRATR showed that ion implantation broke original
PI M. Iwaki, CRC Critical Reviews in Solid State and Material Science, vol. 15. issue 5 (1989) p. 473. and S. Pignataro, Nucl. Instr. and Meth. B39 (1989) 792. M. Iwake, K. Kusakabe. H. [31 Y. Suzuki, M. Kusakabe, Akiba and S. Sato, Mater. Res. Sot. Symp. 110 (1989) 669. [41 Y. Suzuki, M. Kusakabe. M. lwaki and M. Suzuki, Mater. Res. Sot. Symp., in press. ISI Y. Suzuki. M. Kusakabe, M. lwaki and M. Suzuki. Nucl. Instr. and Meth. B32 (1988) 120.
PI G. Marletta
VI. POLYMERS
/ ORGANICS