- Email: [email protected]
Modification of gas separation membranes on a nanometric scale
__ EB
Nuclear Instruments
and Methods in Physics Research B 122
(I 997) 547-549 NNMI
B
Beam Interactions with Materials 8 Atoms
ELSEVIER
Modification of gas separation membranes on a nanometric scale A. T&h a** , I. Be&i a Rrsrurch
L&oratory
a, V.S. Khotimsky
jkr Inorganic
b Institute
’ Depurtment d Department
oj’Electrica1
of theHunguricm
Chemistry
of Petrochemicui
b, G. Marletta ‘, J.L. Sullivan d, S.O. Saied d
Synrhesis oj’Chemistry.
ctnd Electronic
ofthe
Academy c$Sciences.
University
Engineering
P.O. Box 132, H-1518
Russiun Academy nj’Sciences. oj’Busilicuta,
und Applied
Potmx
Physics. (inioersity
Budupest.
Hungory
Mo.wY~)z.,Russiu Italy c)j’Aston. Birminghum,
UK
Abstract Fast atom bombardment (FAB) of or 0.8 keV H beams, with fluences of test gases (He, H,, 0,. N,. CH,) FAB-treated samples were studied by an enrichment of carbon, while SIMS primarily on a nanometric scale.
asymmetric polyvinyltrimethylsilane (PVTMS) membranes by 1 keV Ar, or I keV He, about lOI particles cmm2, resulted in a decrease in the transmembrane flux of various and in a significant increase in the component selectivity. The pristine and the XPS and SIMS. According to XPS results, the FAB-treatment of the membranes led to showed a simultaneous decrease in the hydrogen content in the surface layer, modified
1. Introduction The particle-beam treatment of polymers is increasingly used to alter their properties like wettability, adhesion, biocompatibility, mechanical, electrical, and optical characteristics (see e.g. [l-6]). Recently we presented evidence of the possibility of modifying the mass transport properties of organosilicon polymer based gas separation membranes by particle-beam treatment applied in the low keV energy range [7-IO]. According to current literature data, permeability changes can be observed also in polyimide films, irradiated by high energy ions [I I]. In this article the transport property changes of asymmetric polyvinyltrimethylsilane membranes induced by low energy fast atom beams are discussed, in the light of the surface analytical results obtained by XPS and SIMS.
2. Experimental An asymmetric polyvinyltrimethylsilane (PVTMS) gas separation membrane was studied, obtained by continuous phase inversion process on industrial scale (type: PA-160S-3, I, manufacturer: Kuskovo Chemical Plant, Russia). For particle generation Ar (Linde 4.8 purity). He (Linde Gas Hungary, 4.6). H, (Linde 5.0) were applied. The fast atom beam (FAB) treatment of the gas separation membranes was performed in an equipment described
* Corresponding [email protected].
author.
Fax:
Copyright PII SOl68-583X(96)00760-4
0168-583X/97/$17.00
+ 36-l-3 19-2537;
email:
previously [IO]. The disk-shaped membranes with a diameter of 56 mm were fixed to the sample holder positioned at a distance of 170 mm from the beam aperture. The vacuum chamber was pumped down to lO-6 mbar, then it was purged by the actual treating gas for 5 min at 60 ml s-’ (SIP). The accelerating voltage was I kV for Ar and for He, and 0.8 kV for H. The beam densities for the various gases were determined in blank experiments by the equivalent beam currents measured from secondary emission electron fluxes. Fluences of about IO” particles cmm2 were applied. The transmembrane fluxes for a series of test gases (He. H,, O,, N,, CH,) for the untreated and the particle beam treated membranes were determined by the volumetric method applying a pressure difference of 1.5 bar, at 22°C. The reproducibility of the measurement was +5%. The ideal selectivities for the various gas pairs were calculated as the ratios of the corresponding fluxes. In each case the flux of a gas of smaller effective diameter was related to that of a gas of larger effective diameter. XPS (ESCA) spectra were recorded with a Kratos XSAM800 equipment, using Mg K 0: ,,? radiation, in fixed retardation ratio mode. SIMS studies were performed by a VG Scientific instrument, with target bias = 10 eV. and Ar+ primary beam (5 keV, 0.5 nA).
3. Results and discussion The transmembrane fluxes (F) of the test gases determined for the untreated PVTMS membranes and for their FAB-treated variants, are compiled in Table I. The test
0 1997 Elsevier Science B.V. All rights reserved 111. ION BEAMS
A. T&h er ul. / Nucl. Inrtr. ord Meth. in Phys. Res. B 122 (1997) 547-549
548
gases are listed in increasing order of their effective diameters cd), which are reported to be, as follows: He I;78 A, H, 2.14 A, 0, 2.89 A, N, 3.04 A. and CH, 3.18 A [12]. According to data in Table 1, FAB-treatment decreases the gas fluxes of the PVTMS membranes. Taking the starting F values for lOO%, the percentages obtained after treatments were calculated and given in parentheses. It can be seen that the flux reduction increases with d of the penetrant gases. Regarding the nature of the fast atoms used in the FAB-treatment, the extent of flux reduction changes in the order: Ar < He < H. In Table 2 the ideal component selectivity (cy) is shown for some gas pairs. It is remarkable that the FAB-treatment increases the component selectivity. Taking the Q values of the untreated membranes for lOO%, the corresponding percentages obtained after FAB-treatments were calculated and depicted in Fig. I as a function of the ratios of the effective diameters of the penetrant gases (d,/d,). This figure shows that the selectivity enhancement becomes more pronounced for gas pairs having low d,/d, values. The curves pertaining to treatments by Ar and by He are similar, whereas the curve representing the results of treatment by H reaches significantly higher values of (Y (i.e., more than 900%). XPS measurements performed on the pristine and the FAB-treated PVTMS membranes in enhanced surface sensitivity mode (i.e. at 60” of tilting) testified to the decrease of the Si/C ratio. Furthermore, the shake-up satellite did not arise in the C Is region, and the sample charging did not decrease after FAB treatment. Thus. neither a significant formation of double bonds, nor an increase of conductivity could be detected for the FAB-treated samples. SIMS spectra reflect the dehydrogenation of PVTMS under FAB-treatment: after treatments either by Ar, or by
600 *
0'
0.5
0.6
0.7
0.8
0.9
1.0
4ldB Fig. I, Enhancement of the selectivity to various gas pairs (o.) of the PVTMS membranes after treatment by fast atoms of Ar (0 1, He (0). and H ( A ). (The dashed line corresponds to the untreated membrane.)
He, or especially by H fast atoms, H+ at m/z = 1 is reduced significantly, as compared to the (C,H,)+ type clusters like (C,H.,)+ at m/z = 51. 53 and 55, (C,H,)+ at m/z = 63, 65, 67 and 69, (C,H,)+ at m/z = 77, 79, 81 and 83, and the tropylium ion (C,H,)+ at m/z = 91. The results of TRIM [ 13,141 calculations on the particle distribution for the FAB-treated PVTMS are listed in
Table I Test gas fluxes (F, cm’ cm-’
s-
’ cmHg
'x
lo- 5, for untreated
He Untreated FAB-treated Untreated FAB-treated Untreated FAB-treated
by H
Table 2 Component
selectivities
Untreated FAB-treated Untreated FAB-treated Untreated FAB-treated
by Ar by He
by Ar by He by H
and FAB-treated
PVTMS membranes
H,
0,
N,
CH,
12.0
15.0
3.3
9.8 (82%) 13.5 9.4 (70%) 12.5 5.3 (42%)
I I .o (73%)
I.3 (39%)
17.6 9.4 (53%)
3.1 I .O (32%) 3.3 0.26 (8%)
1.1 0.24 (22%) 0.86 0.18 (21%) 0.92 0.06 (7%)
1.4 0.31 (22%) 1.5 0.27 (I 8%) 1.5 0.07 (5%)
16.5 4.3 (26%)
C(Y) for some gas pairs for untreated
and FAB-treated
PVTMS membranes
He/CH,
H&H,
Ha/N?
H2/02
He/H2
02/N,
8.6 3 I .6 (369%) 9.0 34.8(387%) 8.3 75.7 (909%)
10.7 35.5 (33 I %o) Il.7 34.8 (297%) 11.0 61.4 (558%)
13.6 45.8 (336%) 20.5 52.2 (255%) 17.9 7 I .7 (400%)
4.6 8.5 ( 186%) 5.7 9.4 (I 66%) 5.0 16.5 (331%)
0.8 0.9(111%) 0.8 1.0(130%) 0.8 1.2(163%)
3.0 5.4(181%) 3.6 5.6 (154%) 3.6 4.3 (121%)
A. T6rh et ul. / Nucl. Instr. und Meth. in Phys. Res. B 122
Table 3 TRIM calculations
547-549
549
Acknowledgements for PVTMS
Input purumeters
Ar 1 keV 99999
Particle type Particle energy Number of particles Particle
f 1997)
He I EreV 99999
H 0.8 LieV 99999
Partial financial supports by the Hungarian Research Fund (Project OTKA T-014934) and by the CNR (Italy) are gratefully acknowledged.
disrrihurion
Mean projected range
i
63
234
25.5
Straggling Sliewness Kurtosis
A
19 0.0673 2.7422
98 -0.0193 2.5564
77 -0.7901 3.2320
Lateral projected range
A
12
83
70
Straggling
w
15
104
87
Radial range
A
19
131
110
Straggling
A
IO
68
57
Table 3. It can be seen that the primary modification takes place on a nanometric scale: the mean projected ranges (X) of the primary particles applied are between 6.3 nm and 25.5 nm. The decrease of transmembrane gas flux increases with X of the fast atoms applied. Considering the above data, the observed changes in the mass transport properties of the FAB-treated PVTMS membranes can be connected to the decrease of free volume in the surface layer. This is obviously caused by the extensive structural changes induced by FAB-treatment. The related chemical processes involve preferential elimination of hydrogen and of Si-rich fragments, leaving behind a carbon-enriched surface layer. Since no significant double-bond formation could be detected, the occurrence of crosslinking can be deduced. The formation of crosslinked structures is in agreement with the findings that the FAB-induced reduction of transmembrane flux increases with the effective diameter of the penetrant gas, and that the selectivity enhancement is more pronounced for gas pairs in which the components have strongly different effective diameters.
References
[II Z.W. Kowalski,
J. Mater. Sci. 20 (1985) 152 I. Y.-B. Koh and K. Gamo, Nucl. Instr. and Meth. B SO/81 (19931 1128. 131 J.C. Pivin, P. Viel, G. Zalczer and G. Marletta, Nucl. Instrum. and Meth. B 105 (1995) 192. [41 H. Omichi, Nucl. Instr. and Meth. B 105 (1995) 302. 151 B.A. Ratchev, G.S. Was and J.H. Booske, Nucl. Instr. and Meth. B 106 (1995) 68. [61 G. Marietta and F. Iacona, in: Materials and Processes for Surface and Interface Engineering, ed. Y. Pauleau (Kluwer, Dordrecht, The Netherlands, 1995) pp. 597-640. [71 A. T&h, V.S. Khotimsky, 1. Bert&, N.N. Fateev, T. Sztkely and E.G. Litvinova, in: Abstracts of the 1993 Int. Congr. on Membranes and Membrane Processes, Vol. 2 (ICOM’93, Heidelberg) p. 2.48. RI A. T&h, V.S. Khotimsky, N.N. Fateev. I. Bert&i and T. Szekely, Russian patent 2 072 890 (1996). Dl A. T6th. V.S. Khotimsky, N.N. Fateev, 1. Bert&i and T. Szekely, Hungarian patent 211 184 (1995). [lOI A. T&h, V.S. Khotimsky, I. Bert6ti and G. Marletta, J. Appl. Polym. Sci. 60 (1996) 1883. [III M. Escoubes, J.Y. Dolveck, J. Davenas, X.L. Xu and G. Boiteux, Nucl. Instr. and Meth. B 105 (1995) 130. [I21 V.V. Teplyakov and S.G. Durgarian, Vysokomol. Soedin. 26 A (1984) 1498. [I31 J.P. Biersack and J.F. Ziegler, Transport of Ions in Matter, TRIM, Version 91.14 (IBM Research, Yorktown, NY, USA). [I41 J.F. Ziegler, J.P. Biersack and U. Littmark:. The Stopping and Range of Ions in Solids (Pergamon Press. New York, 1985).
01 J. Yanagisawa.
111. ION BEAMS
Nuclear Instruments
and Methods in Physics Research B 122
(I 997) 547-549 NNMI
B
Beam Interactions with Materials 8 Atoms
ELSEVIER
Modification of gas separation membranes on a nanometric scale A. T&h a** , I. Be&i a Rrsrurch
L&oratory
a, V.S. Khotimsky
jkr Inorganic
b Institute
’ Depurtment d Department
oj’Electrica1
of theHunguricm
Chemistry
of Petrochemicui
b, G. Marletta ‘, J.L. Sullivan d, S.O. Saied d
Synrhesis oj’Chemistry.
ctnd Electronic
ofthe
Academy c$Sciences.
University
Engineering
P.O. Box 132, H-1518
Russiun Academy nj’Sciences. oj’Busilicuta,
und Applied
Potmx
Physics. (inioersity
Budupest.
Hungory
Mo.wY~)z.,Russiu Italy c)j’Aston. Birminghum,
UK
Abstract Fast atom bombardment (FAB) of or 0.8 keV H beams, with fluences of test gases (He, H,, 0,. N,. CH,) FAB-treated samples were studied by an enrichment of carbon, while SIMS primarily on a nanometric scale.
asymmetric polyvinyltrimethylsilane (PVTMS) membranes by 1 keV Ar, or I keV He, about lOI particles cmm2, resulted in a decrease in the transmembrane flux of various and in a significant increase in the component selectivity. The pristine and the XPS and SIMS. According to XPS results, the FAB-treatment of the membranes led to showed a simultaneous decrease in the hydrogen content in the surface layer, modified
1. Introduction The particle-beam treatment of polymers is increasingly used to alter their properties like wettability, adhesion, biocompatibility, mechanical, electrical, and optical characteristics (see e.g. [l-6]). Recently we presented evidence of the possibility of modifying the mass transport properties of organosilicon polymer based gas separation membranes by particle-beam treatment applied in the low keV energy range [7-IO]. According to current literature data, permeability changes can be observed also in polyimide films, irradiated by high energy ions [I I]. In this article the transport property changes of asymmetric polyvinyltrimethylsilane membranes induced by low energy fast atom beams are discussed, in the light of the surface analytical results obtained by XPS and SIMS.
2. Experimental An asymmetric polyvinyltrimethylsilane (PVTMS) gas separation membrane was studied, obtained by continuous phase inversion process on industrial scale (type: PA-160S-3, I, manufacturer: Kuskovo Chemical Plant, Russia). For particle generation Ar (Linde 4.8 purity). He (Linde Gas Hungary, 4.6). H, (Linde 5.0) were applied. The fast atom beam (FAB) treatment of the gas separation membranes was performed in an equipment described
* Corresponding [email protected].
author.
Fax:
Copyright PII SOl68-583X(96)00760-4
0168-583X/97/$17.00
+ 36-l-3 19-2537;
email:
previously [IO]. The disk-shaped membranes with a diameter of 56 mm were fixed to the sample holder positioned at a distance of 170 mm from the beam aperture. The vacuum chamber was pumped down to lO-6 mbar, then it was purged by the actual treating gas for 5 min at 60 ml s-’ (SIP). The accelerating voltage was I kV for Ar and for He, and 0.8 kV for H. The beam densities for the various gases were determined in blank experiments by the equivalent beam currents measured from secondary emission electron fluxes. Fluences of about IO” particles cmm2 were applied. The transmembrane fluxes for a series of test gases (He. H,, O,, N,, CH,) for the untreated and the particle beam treated membranes were determined by the volumetric method applying a pressure difference of 1.5 bar, at 22°C. The reproducibility of the measurement was +5%. The ideal selectivities for the various gas pairs were calculated as the ratios of the corresponding fluxes. In each case the flux of a gas of smaller effective diameter was related to that of a gas of larger effective diameter. XPS (ESCA) spectra were recorded with a Kratos XSAM800 equipment, using Mg K 0: ,,? radiation, in fixed retardation ratio mode. SIMS studies were performed by a VG Scientific instrument, with target bias = 10 eV. and Ar+ primary beam (5 keV, 0.5 nA).
3. Results and discussion The transmembrane fluxes (F) of the test gases determined for the untreated PVTMS membranes and for their FAB-treated variants, are compiled in Table I. The test
0 1997 Elsevier Science B.V. All rights reserved 111. ION BEAMS
A. T&h er ul. / Nucl. Inrtr. ord Meth. in Phys. Res. B 122 (1997) 547-549
548
gases are listed in increasing order of their effective diameters cd), which are reported to be, as follows: He I;78 A, H, 2.14 A, 0, 2.89 A, N, 3.04 A. and CH, 3.18 A [12]. According to data in Table 1, FAB-treatment decreases the gas fluxes of the PVTMS membranes. Taking the starting F values for lOO%, the percentages obtained after treatments were calculated and given in parentheses. It can be seen that the flux reduction increases with d of the penetrant gases. Regarding the nature of the fast atoms used in the FAB-treatment, the extent of flux reduction changes in the order: Ar < He < H. In Table 2 the ideal component selectivity (cy) is shown for some gas pairs. It is remarkable that the FAB-treatment increases the component selectivity. Taking the Q values of the untreated membranes for lOO%, the corresponding percentages obtained after FAB-treatments were calculated and depicted in Fig. I as a function of the ratios of the effective diameters of the penetrant gases (d,/d,). This figure shows that the selectivity enhancement becomes more pronounced for gas pairs having low d,/d, values. The curves pertaining to treatments by Ar and by He are similar, whereas the curve representing the results of treatment by H reaches significantly higher values of (Y (i.e., more than 900%). XPS measurements performed on the pristine and the FAB-treated PVTMS membranes in enhanced surface sensitivity mode (i.e. at 60” of tilting) testified to the decrease of the Si/C ratio. Furthermore, the shake-up satellite did not arise in the C Is region, and the sample charging did not decrease after FAB treatment. Thus. neither a significant formation of double bonds, nor an increase of conductivity could be detected for the FAB-treated samples. SIMS spectra reflect the dehydrogenation of PVTMS under FAB-treatment: after treatments either by Ar, or by
600 *
0'
0.5
0.6
0.7
0.8
0.9
1.0
4ldB Fig. I, Enhancement of the selectivity to various gas pairs (o.) of the PVTMS membranes after treatment by fast atoms of Ar (0 1, He (0). and H ( A ). (The dashed line corresponds to the untreated membrane.)
He, or especially by H fast atoms, H+ at m/z = 1 is reduced significantly, as compared to the (C,H,)+ type clusters like (C,H.,)+ at m/z = 51. 53 and 55, (C,H,)+ at m/z = 63, 65, 67 and 69, (C,H,)+ at m/z = 77, 79, 81 and 83, and the tropylium ion (C,H,)+ at m/z = 91. The results of TRIM [ 13,141 calculations on the particle distribution for the FAB-treated PVTMS are listed in
Table I Test gas fluxes (F, cm’ cm-’
s-
’ cmHg
'x
lo- 5, for untreated
He Untreated FAB-treated Untreated FAB-treated Untreated FAB-treated
by H
Table 2 Component
selectivities
Untreated FAB-treated Untreated FAB-treated Untreated FAB-treated
by Ar by He
by Ar by He by H
and FAB-treated
PVTMS membranes
H,
0,
N,
CH,
12.0
15.0
3.3
9.8 (82%) 13.5 9.4 (70%) 12.5 5.3 (42%)
I I .o (73%)
I.3 (39%)
17.6 9.4 (53%)
3.1 I .O (32%) 3.3 0.26 (8%)
1.1 0.24 (22%) 0.86 0.18 (21%) 0.92 0.06 (7%)
1.4 0.31 (22%) 1.5 0.27 (I 8%) 1.5 0.07 (5%)
16.5 4.3 (26%)
C(Y) for some gas pairs for untreated
and FAB-treated
PVTMS membranes
He/CH,
H&H,
Ha/N?
H2/02
He/H2
02/N,
8.6 3 I .6 (369%) 9.0 34.8(387%) 8.3 75.7 (909%)
10.7 35.5 (33 I %o) Il.7 34.8 (297%) 11.0 61.4 (558%)
13.6 45.8 (336%) 20.5 52.2 (255%) 17.9 7 I .7 (400%)
4.6 8.5 ( 186%) 5.7 9.4 (I 66%) 5.0 16.5 (331%)
0.8 0.9(111%) 0.8 1.0(130%) 0.8 1.2(163%)
3.0 5.4(181%) 3.6 5.6 (154%) 3.6 4.3 (121%)
A. T6rh et ul. / Nucl. Instr. und Meth. in Phys. Res. B 122
Table 3 TRIM calculations
547-549
549
Acknowledgements for PVTMS
Input purumeters
Ar 1 keV 99999
Particle type Particle energy Number of particles Particle
f 1997)
He I EreV 99999
H 0.8 LieV 99999
Partial financial supports by the Hungarian Research Fund (Project OTKA T-014934) and by the CNR (Italy) are gratefully acknowledged.
disrrihurion
Mean projected range
i
63
234
25.5
Straggling Sliewness Kurtosis
A
19 0.0673 2.7422
98 -0.0193 2.5564
77 -0.7901 3.2320
Lateral projected range
A
12
83
70
Straggling
w
15
104
87
Radial range
A
19
131
110
Straggling
A
IO
68
57
Table 3. It can be seen that the primary modification takes place on a nanometric scale: the mean projected ranges (X) of the primary particles applied are between 6.3 nm and 25.5 nm. The decrease of transmembrane gas flux increases with X of the fast atoms applied. Considering the above data, the observed changes in the mass transport properties of the FAB-treated PVTMS membranes can be connected to the decrease of free volume in the surface layer. This is obviously caused by the extensive structural changes induced by FAB-treatment. The related chemical processes involve preferential elimination of hydrogen and of Si-rich fragments, leaving behind a carbon-enriched surface layer. Since no significant double-bond formation could be detected, the occurrence of crosslinking can be deduced. The formation of crosslinked structures is in agreement with the findings that the FAB-induced reduction of transmembrane flux increases with the effective diameter of the penetrant gas, and that the selectivity enhancement is more pronounced for gas pairs in which the components have strongly different effective diameters.
References
[II Z.W. Kowalski,
J. Mater. Sci. 20 (1985) 152 I. Y.-B. Koh and K. Gamo, Nucl. Instr. and Meth. B SO/81 (19931 1128. 131 J.C. Pivin, P. Viel, G. Zalczer and G. Marletta, Nucl. Instrum. and Meth. B 105 (1995) 192. [41 H. Omichi, Nucl. Instr. and Meth. B 105 (1995) 302. 151 B.A. Ratchev, G.S. Was and J.H. Booske, Nucl. Instr. and Meth. B 106 (1995) 68. [61 G. Marietta and F. Iacona, in: Materials and Processes for Surface and Interface Engineering, ed. Y. Pauleau (Kluwer, Dordrecht, The Netherlands, 1995) pp. 597-640. [71 A. T&h, V.S. Khotimsky, 1. Bert&, N.N. Fateev, T. Sztkely and E.G. Litvinova, in: Abstracts of the 1993 Int. Congr. on Membranes and Membrane Processes, Vol. 2 (ICOM’93, Heidelberg) p. 2.48. RI A. T&h, V.S. Khotimsky, N.N. Fateev. I. Bert&i and T. Szekely, Russian patent 2 072 890 (1996). Dl A. T6th. V.S. Khotimsky, N.N. Fateev, 1. Bert&i and T. Szekely, Hungarian patent 211 184 (1995). [lOI A. T&h, V.S. Khotimsky, I. Bert6ti and G. Marletta, J. Appl. Polym. Sci. 60 (1996) 1883. [III M. Escoubes, J.Y. Dolveck, J. Davenas, X.L. Xu and G. Boiteux, Nucl. Instr. and Meth. B 105 (1995) 130. [I21 V.V. Teplyakov and S.G. Durgarian, Vysokomol. Soedin. 26 A (1984) 1498. [I31 J.P. Biersack and J.F. Ziegler, Transport of Ions in Matter, TRIM, Version 91.14 (IBM Research, Yorktown, NY, USA). [I41 J.F. Ziegler, J.P. Biersack and U. Littmark:. The Stopping and Range of Ions in Solids (Pergamon Press. New York, 1985).
01 J. Yanagisawa.
111. ION BEAMS