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Production of particle-track membranes by means of a 5 MV tandem accelerator
Nuclear Instruments and Methods in Physics Research B50 (1990) 395-400 North-Holland
PRODUCTION OF PARTICLE-TRACK TANDEM ACCELERATOR H.B. LijCK, H. MATTHES, and S. TURUC Academy
MEMBRANES
B. GEMENDE,
395
BY MEANS OF A 5 MY
B. HEINRICH,
W. PFESTORF,
W. SEIDEL
of Sciences of the GDR, Central Institute for Nuclear Research at Rossendorj; P. O.B. 19, Dresden, GDR-8051
Beams of Si, Cl and Br ions from a 5 MV tandem accelerator are used for the irradiation of 300 mm wide polyester foil tape. The ions are generated by an inverse caesium sputter source, MISS 688, especially developed for a high beam intensity and a stable operation. The irradiation chamber has a two-compartment design. The foil handling system is installed in the low-vacuum part of the chamber. The foil tape can pass into the high-vacuum part by a vacuum-lock system where it is exposed to the ion beam. In order to achieve a cylindrical shape of the pores down to a pore sire of 30 nm, a very efficient sensibilization procedure was developed. The new solvent-induced sensibilization is completed after two minutes and can be included in the etching equipment. The standard production program comprises 12 different pore diameters ranging from 0.03 to 5 pm.
1. Introduction
2. Irradiation equipment
Membrane filtration and separation have become commonplace in many branches ranging from microelectronics to pharmaceutical production, biotechnology and waste-water recycling. The particle-track technology offers the opportunity of manufacturing membranes with capillary pores of defined pore size and adjustable porosity (1,2]. For the production of particle-track membranes (FTMs), heavy ions like 238U are best suited due to their high specific energy loss. For medium ions like ‘32Xe, an additional UV irradiation is necessary to intensify the radiation damage along the latent particle track in the polymer. By means of a 5 MV tandem accelerator only Si, Cl and Br ions can be accelerated to an energy which is high enough to penetrate through 15, 11 or 8 urn thick polyester foil, respectively. But even after an UV irradiation the track etch rate u, does not achieve that threshold which is necessary to produce fine pores of a really cylindrical shape. Based on the results of our basic research on the mechanism of the track formation and etching in polyesters, a new sensibilization procedure of higher efficiency was developed [3-61. Now a PTM with pores of even 30 nm can be produced from polyester foil. In 1986 the equipment for irradiation of 300 mm wide polyester foil and the etching apparatus were put into operation. Today our standard program comprises 12 different pore sizes ranging from 0.03 to 5 urn [7].
The irradiation is carried out at the 5 MV tandem accelerator which is equipped with an MISS 688 type ion source [8]. This ion source is an inverse caesium sputter source, which was especially developed for the generation of negative heavy ions like Cl-, Br- and I-. It is characterized by a high ion beam intensity, reliable and stable operation and is easy to handle. A cross section of the ion source is shown in fig. 1. The irradiation chamber (figs. 2, 3) consists of two compartments. The low-vacuum compartment contains the tape roll and the driving gear, whereas the irradiation of the tape is performed in the second compartment under high-vacuum conditions. The Faraday cups are also located in the second compartment. A pressure difference of 2-3 orders of magnitude can be maintained between both compartments due to a special design of the irradiation roll. The low-vacuum compartment has a quick-operating door. Thus the time required for tape replacement and restart is about 30 minutes. The irradiation chamber can be utilized for the irradiation of tape material with a maximum width of 300 mm and a length of up to 2000 m, depending on the tape thickness. The ion beam is wobbled by a triangular voltage (7 kV, 1 kHz). The wobbling range is 280 mm at a distance of 9.5 m. The required tape speed is automatically adjusted with respect to the desired pore density and the available ion current. The tape tension is stabilized. The current of the ion beam is monitored during the irradiation process.
0168-583X/90/$03.50 (North-Holland)
0 Elsevier Science Publishers B.V.
VI. ION BEAM MODIFICATION
396
H.B. Liick et al. / Production of particle-track
membranes
3. Chemical processing The processing of the irradiated polyester foil can be carried out some months later, since no fading of the latent tracks has been observed. In order to obtain cylindrical pores, the ratio between the track etch rate u, and the buIk etch rate ub should be as high as possible. Therefore a track sensibilization procedure has to be carried out before etching. 3.1. Sensibilization
Fig. 1. Cross section of the sputter source (model MISS 688): (1) gas spray, (2) cooling, (3) sliding seal, (4) cathode adjustment, (5) gate valve, (6) Cs reservoir, (7) cathode insulator, (8) ionizer heater feedthrough,(9) ace. voltage insulator (10) target pill, (11) ionizer, (12) extractor electrode, (13) acceptance lens.
Since the known sensibilization procedure by an UV irradiation was not efficient enough to get a bigb etch rate ratio, a new sensibilization procedure had to be developed. Based on the assumption that the free volume in the latent track has a dominating influence on the track etch rate [4], a study was undertaken to find a method to increase this free volume. It was known that the amount of free volume in a semicrystalline polymer
Fig. 2. Photo of the irradiation equipment.
H.B. Liick et al. / Production of particle-track
391
membranes
Fig. 3. Schematic cross section of the irradiation chamber: (1) vacuum chamber, (2,3) pumps, (4,5) tape rolls, (6) vacuumlock with irradiation roll, (7) Faraday cups.
like polyester
can
be enlarged
by
a solvent-induced
[9,10]. This effect can be used to improve the dye uptake and the rate of dying of polyester yarns. In this case organic solvents are applied which have a similar solubility parameter 6, such as polyester. The solubility parameter is the square root of the cohesive energy density, i.e. the energy of vaporization per volume element. The solubility parameters of the applied solvents are listed in table 2. organic solvents which have a similar solubility parameter as polyester can penetrate into the polymer martix and induce a crystallization of the amorphous regions in the polymer [ 111. But a sensibilization effect results only when the degree crystallization
Table 1 Irradiation parameters membranes Pore size
Particle
for the production
Energy
Current
[Meal
[IN
Tape speed
Tape thickness
b/s1
[pm1
40 40 40
150 150 100
0.04-0.01 0.16-1.0 1
8 10 15
Iwl 0.03-0.1 0.2 -0.8 1.0 -5.0
81Br7+ 35C17+ “Si’+
of particle-track
Table 2 Effect of solvents of different solubility parameters 6 on the etch rate of Ar tracks in polyester Solvent
6.10-3 [J’/Z/m3’2]
“ts/%o
Dimethylformamide Pyridine s-Tetrachloroethane Dioxane Tetrahydrofuran Benzyl alcohol Methyl salicylate Cyclohexanol
24.1 21.6 20.1 20.4 19.4 24.7 20.8 22.3
37 34.4 31.8 31.2 22.1 22.1 2.5 1.0
71
-L
0
5
10 ts[minl
15
Fig. 4. Effect of temperature and time of the DMF-treatment, t,, on the breakthrough time tb of particle-track etching.
of solvent-induced crystallization and swelling is more pronounced in the latent track than in the surrounding bulk polymer. This concept was tested by the effect of eight solvents on the etch rate of 40Ar tracks in polyester. It was proved that the bulk etch rate was not influenced by the solvent treatment. The irradiated samples were immersed in the solvents for 8 minutes at a temperature of 70 o C. The solvent treatment was followed by a solvent exchange with ethanol at room temperature for 15 minutes, since some, solvents were not mixable with the etchant. It was proved that ethanol has no influence on the sensibilization effect. The resulting track etch rate vts was normalized on the track etch rate without sensibilization, vt,,. The results were summarized in table 2. In a second test the influence of the temperature and the treatment time were investigated for a sensibilization by dimethylformamide (DMF) (fig. 4). The breakthrough time t, was used as a measure for the sensibilization effect. Etching was carried out from both sides and t, is the time elapsed until the etch channels meet. It can be concluded from the curve in fig. 4 that for a treatment temperature of 70°C the crystallization process is completed after 2 minutes. A longer treatment time has no influence on vtS. The same tracks were exposed to an intensive UV irradiation for 3 hours. The track etch rate increased only by a factor of 2.1 compared to a factor of 37 for the DMF-treatment. For the production of particle-track membranes, DMF has been VI. ION BEAM MODIFICATION
H.B. Liick et al. / Production of particle-track
398
membranes
Fig. 5. Photo of the sensibilization and etching apparatus.
n due to its high efficiency and the reliable results. procedure, it became posUsing the new sensibilization sible t.o produce F’TMs of 30 run pore size from polyester.
3.2. Chemical
etching
The new sensibilization procedure can be performed together with the chemical etching in the same appara-
PTM
irradiakd polyester
tope
1
2
3
G
5
6
9
70 0 15
Fig. 6. Scheme of the arrangement of the baths in the etching apparatus: (1) sensibilization, DMF, 70 o C; (2) rinsi w, etching, SN NaOH, 40-70 o C; (5) stopping, HAc; (6-8) rinsing, H,O; (9) drying, hot air.
H,O;
(334)
H. B. Liick et al. / Production of particle-track
membranes
399
Fig. 7. Cross section of a FTM broken in liquid nitrogen.
tus, shown inI fig. 5. The DMF bath is followed by a wate:r bath in order to exchange and remove the DMF fron 1 the tape before it passes through the etching baths (fig. 6). The t emperature of the etchant (5M NaOH) is kept constant within a range of f 0.1 o C by means of a
thermostatic system. The pore size is controlled by the etching time and the temperature of the etchant. The etchant has to be circulated by pumps in order to a’void a temperature gradient. By this means the pore size can be kept within a tolerance of f5%. The pore diamieter
Fig. 8. Particulatesseparatedfrom ultrapure water by a FTM. VI. ION BEAM MODIFICATION
400
H.B. L&k et al. / ~r~uctio~
o~particie-track
membr~es
Fig. 9. PTM used for the cross-flow filtration of vine. is checked during the production by a bubble point test. Our production program includes 12 different pore sizes ranging from 0.03 to 5 *m.
4. Perfomance
For the industrial application the FTM is reinforced by a polyester fleece in order to increase its mechanical strength and to improve the handling of the membrane. The main application is the cross-flow filtration on the pilot and industrial scale.
advantages and application of PTMs
The PTM is the only membrane which has really cylindrical pores (fig. 7) of a defined size and an adjustable pore density. The smooth surface of this ideal surface filter offers a superior material for the cross-flow filtration and the separation and analysis of particnlates (figs. 8, 9). The PTM made from polyester is free from plasticizers, extractables and surfactants. The membrane is not cytotoxic or bacteriostatic. PTMs are characterized by a high mechanical strength and an excellent chemical resistance. Therefore the membrane is best suited for a wide range of applications in the laboratory and for analysis. Some typical applications are listed in the following: - preparation of ultrapure liquids, - particulate analysis, - analysis of dust and aerosoles, - epifluorescence microscopy, - preparation of biosensores and enzyme electrodes.
References R.L. Fleischer, P.R. Price and R.M. Walker, Nuclear Tracks in Sohds: Principles and Apphcations (Univ. of California, Berkeley, 1975). C. Bieth, M. Van den Bossche, D. Busardo, E. BaIanzat, P. Pierrard and J. Meslage, CANIL A 88-04. H.B. L&k, DDR-WP 235 923 (1980). H.B. Luck, NucI. Instr. and Meth. 200 (1982) 517. H.B. Lbck, Nucl. Instr. and Meth. 202 (1982) 497. H.B. Luck, Nucl. Instr. and Meth. 213 (1983) 507. Produktinformation Kapillarporenmembranen fiir Analyse und Labor (ZfK Rossendorf, 1989). H. Matthes, W. Pfestorf and L. Steinert, Nucl. Instr. and Meth. 220 (1984) 112. R.H. Knox, H.D. Weigmann and M.G. Scott, Textile Res. J. 45 (1975) 203. H.D. Wei$mann, M.G. Scott, AS. Ribnick and R.D. Matkowsky, Textile Res. J. 47 (1977) 745. A.K. Kuis~eshtha, A.H. Kahn and G.L. Madan, PoIymer 19 (1978) 819.
PRODUCTION OF PARTICLE-TRACK TANDEM ACCELERATOR H.B. LijCK, H. MATTHES, and S. TURUC Academy
MEMBRANES
B. GEMENDE,
395
BY MEANS OF A 5 MY
B. HEINRICH,
W. PFESTORF,
W. SEIDEL
of Sciences of the GDR, Central Institute for Nuclear Research at Rossendorj; P. O.B. 19, Dresden, GDR-8051
Beams of Si, Cl and Br ions from a 5 MV tandem accelerator are used for the irradiation of 300 mm wide polyester foil tape. The ions are generated by an inverse caesium sputter source, MISS 688, especially developed for a high beam intensity and a stable operation. The irradiation chamber has a two-compartment design. The foil handling system is installed in the low-vacuum part of the chamber. The foil tape can pass into the high-vacuum part by a vacuum-lock system where it is exposed to the ion beam. In order to achieve a cylindrical shape of the pores down to a pore sire of 30 nm, a very efficient sensibilization procedure was developed. The new solvent-induced sensibilization is completed after two minutes and can be included in the etching equipment. The standard production program comprises 12 different pore diameters ranging from 0.03 to 5 pm.
1. Introduction
2. Irradiation equipment
Membrane filtration and separation have become commonplace in many branches ranging from microelectronics to pharmaceutical production, biotechnology and waste-water recycling. The particle-track technology offers the opportunity of manufacturing membranes with capillary pores of defined pore size and adjustable porosity (1,2]. For the production of particle-track membranes (FTMs), heavy ions like 238U are best suited due to their high specific energy loss. For medium ions like ‘32Xe, an additional UV irradiation is necessary to intensify the radiation damage along the latent particle track in the polymer. By means of a 5 MV tandem accelerator only Si, Cl and Br ions can be accelerated to an energy which is high enough to penetrate through 15, 11 or 8 urn thick polyester foil, respectively. But even after an UV irradiation the track etch rate u, does not achieve that threshold which is necessary to produce fine pores of a really cylindrical shape. Based on the results of our basic research on the mechanism of the track formation and etching in polyesters, a new sensibilization procedure of higher efficiency was developed [3-61. Now a PTM with pores of even 30 nm can be produced from polyester foil. In 1986 the equipment for irradiation of 300 mm wide polyester foil and the etching apparatus were put into operation. Today our standard program comprises 12 different pore sizes ranging from 0.03 to 5 urn [7].
The irradiation is carried out at the 5 MV tandem accelerator which is equipped with an MISS 688 type ion source [8]. This ion source is an inverse caesium sputter source, which was especially developed for the generation of negative heavy ions like Cl-, Br- and I-. It is characterized by a high ion beam intensity, reliable and stable operation and is easy to handle. A cross section of the ion source is shown in fig. 1. The irradiation chamber (figs. 2, 3) consists of two compartments. The low-vacuum compartment contains the tape roll and the driving gear, whereas the irradiation of the tape is performed in the second compartment under high-vacuum conditions. The Faraday cups are also located in the second compartment. A pressure difference of 2-3 orders of magnitude can be maintained between both compartments due to a special design of the irradiation roll. The low-vacuum compartment has a quick-operating door. Thus the time required for tape replacement and restart is about 30 minutes. The irradiation chamber can be utilized for the irradiation of tape material with a maximum width of 300 mm and a length of up to 2000 m, depending on the tape thickness. The ion beam is wobbled by a triangular voltage (7 kV, 1 kHz). The wobbling range is 280 mm at a distance of 9.5 m. The required tape speed is automatically adjusted with respect to the desired pore density and the available ion current. The tape tension is stabilized. The current of the ion beam is monitored during the irradiation process.
0168-583X/90/$03.50 (North-Holland)
0 Elsevier Science Publishers B.V.
VI. ION BEAM MODIFICATION
396
H.B. Liick et al. / Production of particle-track
membranes
3. Chemical processing The processing of the irradiated polyester foil can be carried out some months later, since no fading of the latent tracks has been observed. In order to obtain cylindrical pores, the ratio between the track etch rate u, and the buIk etch rate ub should be as high as possible. Therefore a track sensibilization procedure has to be carried out before etching. 3.1. Sensibilization
Fig. 1. Cross section of the sputter source (model MISS 688): (1) gas spray, (2) cooling, (3) sliding seal, (4) cathode adjustment, (5) gate valve, (6) Cs reservoir, (7) cathode insulator, (8) ionizer heater feedthrough,(9) ace. voltage insulator (10) target pill, (11) ionizer, (12) extractor electrode, (13) acceptance lens.
Since the known sensibilization procedure by an UV irradiation was not efficient enough to get a bigb etch rate ratio, a new sensibilization procedure had to be developed. Based on the assumption that the free volume in the latent track has a dominating influence on the track etch rate [4], a study was undertaken to find a method to increase this free volume. It was known that the amount of free volume in a semicrystalline polymer
Fig. 2. Photo of the irradiation equipment.
H.B. Liick et al. / Production of particle-track
391
membranes
Fig. 3. Schematic cross section of the irradiation chamber: (1) vacuum chamber, (2,3) pumps, (4,5) tape rolls, (6) vacuumlock with irradiation roll, (7) Faraday cups.
like polyester
can
be enlarged
by
a solvent-induced
[9,10]. This effect can be used to improve the dye uptake and the rate of dying of polyester yarns. In this case organic solvents are applied which have a similar solubility parameter 6, such as polyester. The solubility parameter is the square root of the cohesive energy density, i.e. the energy of vaporization per volume element. The solubility parameters of the applied solvents are listed in table 2. organic solvents which have a similar solubility parameter as polyester can penetrate into the polymer martix and induce a crystallization of the amorphous regions in the polymer [ 111. But a sensibilization effect results only when the degree crystallization
Table 1 Irradiation parameters membranes Pore size
Particle
for the production
Energy
Current
[Meal
[IN
Tape speed
Tape thickness
b/s1
[pm1
40 40 40
150 150 100
0.04-0.01 0.16-1.0 1
8 10 15
Iwl 0.03-0.1 0.2 -0.8 1.0 -5.0
81Br7+ 35C17+ “Si’+
of particle-track
Table 2 Effect of solvents of different solubility parameters 6 on the etch rate of Ar tracks in polyester Solvent
6.10-3 [J’/Z/m3’2]
“ts/%o
Dimethylformamide Pyridine s-Tetrachloroethane Dioxane Tetrahydrofuran Benzyl alcohol Methyl salicylate Cyclohexanol
24.1 21.6 20.1 20.4 19.4 24.7 20.8 22.3
37 34.4 31.8 31.2 22.1 22.1 2.5 1.0
71
-L
0
5
10 ts[minl
15
Fig. 4. Effect of temperature and time of the DMF-treatment, t,, on the breakthrough time tb of particle-track etching.
of solvent-induced crystallization and swelling is more pronounced in the latent track than in the surrounding bulk polymer. This concept was tested by the effect of eight solvents on the etch rate of 40Ar tracks in polyester. It was proved that the bulk etch rate was not influenced by the solvent treatment. The irradiated samples were immersed in the solvents for 8 minutes at a temperature of 70 o C. The solvent treatment was followed by a solvent exchange with ethanol at room temperature for 15 minutes, since some, solvents were not mixable with the etchant. It was proved that ethanol has no influence on the sensibilization effect. The resulting track etch rate vts was normalized on the track etch rate without sensibilization, vt,,. The results were summarized in table 2. In a second test the influence of the temperature and the treatment time were investigated for a sensibilization by dimethylformamide (DMF) (fig. 4). The breakthrough time t, was used as a measure for the sensibilization effect. Etching was carried out from both sides and t, is the time elapsed until the etch channels meet. It can be concluded from the curve in fig. 4 that for a treatment temperature of 70°C the crystallization process is completed after 2 minutes. A longer treatment time has no influence on vtS. The same tracks were exposed to an intensive UV irradiation for 3 hours. The track etch rate increased only by a factor of 2.1 compared to a factor of 37 for the DMF-treatment. For the production of particle-track membranes, DMF has been VI. ION BEAM MODIFICATION
H.B. Liick et al. / Production of particle-track
398
membranes
Fig. 5. Photo of the sensibilization and etching apparatus.
n due to its high efficiency and the reliable results. procedure, it became posUsing the new sensibilization sible t.o produce F’TMs of 30 run pore size from polyester.
3.2. Chemical
etching
The new sensibilization procedure can be performed together with the chemical etching in the same appara-
PTM
irradiakd polyester
tope
1
2
3
G
5
6
9
70 0 15
Fig. 6. Scheme of the arrangement of the baths in the etching apparatus: (1) sensibilization, DMF, 70 o C; (2) rinsi w, etching, SN NaOH, 40-70 o C; (5) stopping, HAc; (6-8) rinsing, H,O; (9) drying, hot air.
H,O;
(334)
H. B. Liick et al. / Production of particle-track
membranes
399
Fig. 7. Cross section of a FTM broken in liquid nitrogen.
tus, shown inI fig. 5. The DMF bath is followed by a wate:r bath in order to exchange and remove the DMF fron 1 the tape before it passes through the etching baths (fig. 6). The t emperature of the etchant (5M NaOH) is kept constant within a range of f 0.1 o C by means of a
thermostatic system. The pore size is controlled by the etching time and the temperature of the etchant. The etchant has to be circulated by pumps in order to a’void a temperature gradient. By this means the pore size can be kept within a tolerance of f5%. The pore diamieter
Fig. 8. Particulatesseparatedfrom ultrapure water by a FTM. VI. ION BEAM MODIFICATION
400
H.B. L&k et al. / ~r~uctio~
o~particie-track
membr~es
Fig. 9. PTM used for the cross-flow filtration of vine. is checked during the production by a bubble point test. Our production program includes 12 different pore sizes ranging from 0.03 to 5 *m.
4. Perfomance
For the industrial application the FTM is reinforced by a polyester fleece in order to increase its mechanical strength and to improve the handling of the membrane. The main application is the cross-flow filtration on the pilot and industrial scale.
advantages and application of PTMs
The PTM is the only membrane which has really cylindrical pores (fig. 7) of a defined size and an adjustable pore density. The smooth surface of this ideal surface filter offers a superior material for the cross-flow filtration and the separation and analysis of particnlates (figs. 8, 9). The PTM made from polyester is free from plasticizers, extractables and surfactants. The membrane is not cytotoxic or bacteriostatic. PTMs are characterized by a high mechanical strength and an excellent chemical resistance. Therefore the membrane is best suited for a wide range of applications in the laboratory and for analysis. Some typical applications are listed in the following: - preparation of ultrapure liquids, - particulate analysis, - analysis of dust and aerosoles, - epifluorescence microscopy, - preparation of biosensores and enzyme electrodes.
References R.L. Fleischer, P.R. Price and R.M. Walker, Nuclear Tracks in Sohds: Principles and Apphcations (Univ. of California, Berkeley, 1975). C. Bieth, M. Van den Bossche, D. Busardo, E. BaIanzat, P. Pierrard and J. Meslage, CANIL A 88-04. H.B. L&k, DDR-WP 235 923 (1980). H.B. Luck, NucI. Instr. and Meth. 200 (1982) 517. H.B. Lbck, Nucl. Instr. and Meth. 202 (1982) 497. H.B. Luck, Nucl. Instr. and Meth. 213 (1983) 507. Produktinformation Kapillarporenmembranen fiir Analyse und Labor (ZfK Rossendorf, 1989). H. Matthes, W. Pfestorf and L. Steinert, Nucl. Instr. and Meth. 220 (1984) 112. R.H. Knox, H.D. Weigmann and M.G. Scott, Textile Res. J. 45 (1975) 203. H.D. Wei$mann, M.G. Scott, AS. Ribnick and R.D. Matkowsky, Textile Res. J. 47 (1977) 745. A.K. Kuis~eshtha, A.H. Kahn and G.L. Madan, PoIymer 19 (1978) 819.