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Removal of toxic gas by hybrid chemical filter fabricated by the sequential adsorption of polymers
Thin Solid Films 393 Ž2001. 243᎐248
Removal of toxic gas by hybrid chemical filter fabricated by the sequential adsorption of polymers S. ShiratoriU , Y. Inami, M. Kikuchi Department of Applied Physics & Physico-infomatics, Keio Uni¨ ersity, Hiyoshi Kouhoku-ku, Yokohama 223-8522, Japan
Abstract A high-performance chemical filter for toxic gas, such as ammonia or acetaldehyde, was newly fabricated by forming a layer-by-layer self-assembly film on the surface of a fiberglass cloth. The filter was greatly superior to the conventional active carbon filter. The newly developed filter showed remarkably high performance, because it can adsorb large amounts of gas molecules by both chemical and physical adsorption. Ammonia or acetaldehyde gases react with the polyelectrolytes in the film and are adsorbed into the multilayers of the films. In this paper, we report that the performance of the chemical filter is dependent on the nano-structure of the thin polymer film coated on the fiberglass cloth. 䊚 2001 Elsevier Science B.V. All rights reserved. Keywords: Toxic gas; Chemical filter; Polymer film
1. Introduction Non-smoking areas have expanded widely in various locations, such as airports, stations, trains and offices, and smoking in only limited areas is strongly enforced. The American Lung Association ŽALA, 1993. reported 53 000 cases of death from passive smoking, 3000 of lung cancer, 37 000 of heart disease, and 13 000 of other cancers. High-quality air cleaners are required to prevent diseases caused by passive smoking. On the other hand, after the so-called ‘oil shock’ in the 1970s, from the point of view of energy conservation, numbers of buildings and houses which have high adiabatic or airtight characteristics have been increasing. As a result, the incidence of so-called ‘sick building syndrome’ is increasing. Not only due to passive smoking, it has been pointed out that one of the main reasons for the syndrome is the toxic gas that evaporates from the adhesive used in blockboard and other housing materials. It has also been pointed out that
people today tend to spend 90% of their day not outdoors, but indoors. Therefore, high-performance air cleaners or new functional materials which can adsorb and remove toxic gas, such as formaldehyde that diffuses from furniture or wallpaper, are required. Recently, we found that layer-by-layer self-assembly films prepared from polylectrolytes w1,2x have the characteristics to adsorb toxic gas, such as ammonia, acetaldehyde, or smoke w3x. The adsorption mechanism includes both physical and chemical adsorption. By utilizing the unique adsorption characteristics, a highperformance chemical filter was fabricated by coating the surface of the fiberglass cloth with a polyelectrolyte thin film in order to construct comfortable living environment which is friendly to human health. In this paper, we present the removal characteristics of layerby-layer self-assembly films for toxic gases, which are strongly dependent on the nano-structure of the thin film. 2. Experimental
U
Corresponding author. Tel.: q81-45-566-1602; fax: q81-45-5661602. E-mail address: [email protected] ŽS. Shiratori..
An automatic dipping machine with a computer-controlled film mass system w1᎐3x was used for depositing
0040-6090r01r$ - see front matter 䊚 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 4 0 - 6 0 9 0 Ž 0 1 . 0 1 0 7 6 - 8
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S. Shiratori et al. r Thin Solid Films 393 (2001) 243᎐248
layer-by-layer self-assembly films. In this system, the data acquired during adsorption are fed back using a quartz crystal microbalance ŽQCM. to control the dipping time. Thus, high-quality self-assembled films were produced, because the thickness of each adsorbing layer was systematically controlled with nm-scale accuracy. We call this new type of polymer thin film a mass-controlled layer-by-layer self-assembly film w3᎐6x. The advantage of this type of film is that the microstructure and the mass ratio of polycationrpolyanion can be systematically controlled. A schematic image to show the structure of the new filter developed using the layer-by-layer sequential adsorption of polyelectrolytes in this study is shown in Fig. 1. The permeation characteristics of smoke or toxic gas into the filter are predicted to be high, because the film is very porous. Smoke or toxic gas is adsorbed by the film due to coulombic force and to the chemical reaction between the polymer and the toxic gas. Therefore, the air containing toxic gas will be cleaned after passing through the film. In this study, the following polymers were used for the deposition of layer-by-layer sequential adsorbed films: polyŽallylamine hydrochloride. ŽPAH. as polycation and polyŽacrylic acid. ŽPAA. as polyanion. For the
Fig. 1. Schematic illustration of the mechanism of the gas-adsorption image using a layer-by-layer self-assembly film.
Fig. 2. Experimental set-up to measure the filter performance.
deposition of film using the polyelectrolyte solutions, the pH of each solution was adjusted with NaOH or HCl solution. Up to 100 bilayers of the layer-by-layer sequentially adsorbed films were deposited on the surface of fiberglass cloths. The diameter of the fiber was 6 m. After deposition, the cloths were dried at 90⬚C in an oven. The performance of the filter was evaluated using static and gas-flow systems. For the static system, the top of an open vessel was covered by a filter sheet and the whole assembly was enclosed in a vinyl bag. The gas permeated through the filter was evaluated by measuring the gas concentration in the vinyl bag Žoutside of the vessel.. The experimental set-up of the gas flow system is shown in Fig. 2. As shown in Fig. 2, the concentration of the gas before and after passing through the filter was measured and compared. Ammonia and acetaldehyde were used as toxic gases for evaluation of the filter performance. The proof-reading gas was generated by the permeator, as shown in Fig. 3. This equipment produces a standard gas flow with constant concentration. Measurement of the gas concentration before and after passing through the filter was evaluated with gas detector tubes ŽGastec no. 91, 91L, 91LL, 91P, 91PL, 3L, 3M and 3LA.. The decrease in toxic gas concentration in the closed chamber was examined for the novel polyelectrolyte chemical filter. The surface structure of the layer-by-layer self assembly film was observed using an atomic force microscope ŽAFM. and a field-emission scanning electron microscope ŽFESEM..
Fig. 3. Gas proof-reading device.
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3. Results and discussions First, the performance of the filter was evaluated in a static system. The filter performance for the adsorption of ammonia or acetaldehyde is shown in Fig. 4. The figure shows the number of bilayers of the film vs. gas concentration after passing through filter. As the number of bilayers increases, the adsorption characteristics of the filters for ammonia gas improved. As shown in the figure, the filter fabricated with 100 bilayers removed 96% of the ammonia gas. Similar results were obtained for the case of acetaldehyde gas, although the removal ratio was 76%. The result measured by the ammonia gas-flow system is shown in Fig. 5. Similar results were obtained with the static system. The concentration of ammonia after passing through the filter decreased as the number of bilayers increased. A similar result was obtained for acetaldehyde. The adsorption mechanism of the coated polyelectrolytes was investigated using IR absorbance spectroscopy. Absorbance spectra of PAA films withrwithout exposure to ammonia are shown in Fig. 6a. Peaks corresponding to amide are shown in the range 1580᎐1680 cmy1 . One of the largest peaks in the spectrum, which was not observed for PAA cast film, was observed at 1650 cmy1 in the film after exposure to an ammonia atmosphere. Absorbance spectra of PAH cast films withrwithout exposure to an acetaldehyde atmosphere are shown in Fig. 6b. Maximum absorbance was observed in the range 1600᎐1680 cmy1 . In this study, a peak, which was not observed for PAH cast film, was clearly observed at 1570 cmy1 in the
Fig. 4. Change in the adsorption characteristics of ammonia and acetaldehyde gas with increasing number of bilayers in the static system.
Fig. 5. Ammonia adsorption effect of the fabricated filter in the gas flow system.
PAH film after exposure to an acetaldehyde atmosphere. Therefore, it was considered that ammonia is chemically adsorbed by PAA layers and acetaldehyde by PAH layers. The possible reactions are shown in the following. Ammonia gas reacts with carboxyl groups and amide is generated. The reaction is shown by formula Ža..
Acetaldehyde gas reacts with primary amine groups. The reaction is shown as formula Žb..
A comparison of the acetaldehyde adsorbance efficiency of the PAH cast film with active carbon is shown in Fig. 7. For this examination, the same mass of the PAH cast film and active carbon were compared, with both prepared on slide glasses. As shown in this figure, the adsorption efficiency of the PAH cast film was better than that of active carbon before annealing. In the case of active carbon, reemission of adsorbed gas molecules was often observed, because the adsorption of gas molecules was caused by physical adsorption. On the other hand, in the case of PAH films, reemission of adsorbed gas molecules was seldom observed, because the gas molecules were chemically adsorbed by the films. In a previous study, we reported that the nano-structure of the layer-by-layer self-assembled films changes according to the solution pH of the adsorbing bath w1,2x. To examine the relationship between the microscopic structure of the polyelectrolyte thin film and the
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S. Shiratori et al. r Thin Solid Films 393 (2001) 243᎐248
Fig. 6. Ža. FTIR absorbance spectra of PAA cast films before and after exposure to ammonia atmosphere. Žb. FTIR absorbance spectra of PAH cast films before and after exposure to acetaldehyde atmosphere.
gas adsorption characteristics, the response characteristics to different concentrations of ammonia gas were studied using the quartz crystal microbalance ŽQCM. technique. Different types of nano-structures were formed by changing the solution pH of the polyelectrolytes w2x. The results are shown in Fig. 8. Fig. 8a shows the case when the polyelectrolyte film was deposited at pH 5.0 for PAH and pH 5.0 for PAA, and Fig. 8b the case when the polyelectrolyte film was deposited at pH 7.5 for PAH and pH 3.5 for PAA. As shown in the figure, the adsorption characteristics of the former are lower than the latter. In order to examine the surface structure of the
films, the surfaces were observed by atomic force microscopy ŽAFM.. The images are shown in Fig. 9a,b. In Fig. 9a, the film formed has a looped, porous structure, and in Fig. 9b, the polyelectrolyte films has a textile-like structure. RMS measurement of the surface roughness gave approximately 2 nm for Fig. 9a and 30 nm for Fig. 9b. We consider that the differences in gas adsorption characteristics were caused by the difference in the surface arearvolume ratio of the polyelectrolyte films. FESEM images of the bare cloth and the fiberglass cloth coated with the layer-by-layer self-assembly films are shown in Fig. 10a,b, respectively. As shown in the figure, the surface of the fiberglass cloth was uniformly
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Fig. 7. Comparison of the acetaldehyde absorption efficiency between PAH film and conventional active carbon.
coated by the self-assembled film, with nm-scale pores. These nano-pores were found to be extremely effective in improving the adsorption characteristics of the filter for toxic gas. Increasing the surface area and optimization of the materials and deposition conditions is in progress for the practical production of high-quality filters for removing various toxic gases. 4. Conclusions We have demonstrated the high performance of a polymer thin film, prepared by the layer-by-layer adsorption technique of polyelectrolytes films, as a filter for toxic gases, such as ammonia or acetaldehyde. The adsorption characteristics of the filter membrane for the toxic gas can be optimized by changing the deposi-
Fig. 9. AFM images of Ža. loopy; and Žb. textile structure Žboth 10 = 10 m2 ..
tion condition, such as pH of the adsorption solution, or the number of bilayers in the films. Consequently, these thin polymer films can be used as a new type of high-performance filter for air cleaning, which has remarkable adsorption characteristics for various toxic gases. Acknowledgements
Fig. 8. Difference in the adsorption characteristics for ammonia caused by the nano-structure of the thin film. Ža. PAH ŽpH 5.0.rPAA ŽpH 5.0.; and Žb. PAH ŽpH 7.5.rPAAŽpH 3.5..
A part of this work was supported by the Nippon Sheet Glass Foundation for Materials Science and Engineering Ž2000., the Mitsubishi Foundation Ž2000., and the Japan Science and Technology Corporation ŽJST.. The fiberglass cloth was supplied by Mie Textile Corporation, Japan. We thank Prof Rubner of the Massachusetts Institute of Technology for his advice on
S. Shiratori et al. r Thin Solid Films 393 (2001) 243᎐248
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Fig. 10. FESEM images of the bare fiberglass cloth and the fiberglass cloth coated with the layer-by-layer self-assembled film.
the layer-by-layer self-assembly technique. We also acknowledge Mr Takeaki Kitamura of Mie Textile Corporation for offering the various fiberglass textiles and for his advice on the fiberglass cloths. References w1x D. Yoo, S.S. Shiratori, M.F. Rubner, Macromolecules 31 Ž1998. 4309.
w2x S. Shiratori, M.F. Rubner, Macromolecules 33 Ž2000. 4213. w3x Japanese patent application, no. 10-10-267286r1998, 11-077553, 11-077554. w4x S.S. Shiratori, M. Yamada, Polym. Adv. Technol. 11 Ž2000. 810. w5x S.S. Siratori, Y. Inami, M. Kikuchi, Trans. Mater. Res. Soc. Jpn. 25 Ž2. Ž2000. 401. w6x S.S. Shiratori, Y. Inami, M. Kichiku, M. Yamada, T. Yamada, Polym. Adv. Technol. 11 Ž2000. 766.
Removal of toxic gas by hybrid chemical filter fabricated by the sequential adsorption of polymers S. ShiratoriU , Y. Inami, M. Kikuchi Department of Applied Physics & Physico-infomatics, Keio Uni¨ ersity, Hiyoshi Kouhoku-ku, Yokohama 223-8522, Japan
Abstract A high-performance chemical filter for toxic gas, such as ammonia or acetaldehyde, was newly fabricated by forming a layer-by-layer self-assembly film on the surface of a fiberglass cloth. The filter was greatly superior to the conventional active carbon filter. The newly developed filter showed remarkably high performance, because it can adsorb large amounts of gas molecules by both chemical and physical adsorption. Ammonia or acetaldehyde gases react with the polyelectrolytes in the film and are adsorbed into the multilayers of the films. In this paper, we report that the performance of the chemical filter is dependent on the nano-structure of the thin polymer film coated on the fiberglass cloth. 䊚 2001 Elsevier Science B.V. All rights reserved. Keywords: Toxic gas; Chemical filter; Polymer film
1. Introduction Non-smoking areas have expanded widely in various locations, such as airports, stations, trains and offices, and smoking in only limited areas is strongly enforced. The American Lung Association ŽALA, 1993. reported 53 000 cases of death from passive smoking, 3000 of lung cancer, 37 000 of heart disease, and 13 000 of other cancers. High-quality air cleaners are required to prevent diseases caused by passive smoking. On the other hand, after the so-called ‘oil shock’ in the 1970s, from the point of view of energy conservation, numbers of buildings and houses which have high adiabatic or airtight characteristics have been increasing. As a result, the incidence of so-called ‘sick building syndrome’ is increasing. Not only due to passive smoking, it has been pointed out that one of the main reasons for the syndrome is the toxic gas that evaporates from the adhesive used in blockboard and other housing materials. It has also been pointed out that
people today tend to spend 90% of their day not outdoors, but indoors. Therefore, high-performance air cleaners or new functional materials which can adsorb and remove toxic gas, such as formaldehyde that diffuses from furniture or wallpaper, are required. Recently, we found that layer-by-layer self-assembly films prepared from polylectrolytes w1,2x have the characteristics to adsorb toxic gas, such as ammonia, acetaldehyde, or smoke w3x. The adsorption mechanism includes both physical and chemical adsorption. By utilizing the unique adsorption characteristics, a highperformance chemical filter was fabricated by coating the surface of the fiberglass cloth with a polyelectrolyte thin film in order to construct comfortable living environment which is friendly to human health. In this paper, we present the removal characteristics of layerby-layer self-assembly films for toxic gases, which are strongly dependent on the nano-structure of the thin film. 2. Experimental
U
Corresponding author. Tel.: q81-45-566-1602; fax: q81-45-5661602. E-mail address: [email protected] ŽS. Shiratori..
An automatic dipping machine with a computer-controlled film mass system w1᎐3x was used for depositing
0040-6090r01r$ - see front matter 䊚 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 4 0 - 6 0 9 0 Ž 0 1 . 0 1 0 7 6 - 8
244
S. Shiratori et al. r Thin Solid Films 393 (2001) 243᎐248
layer-by-layer self-assembly films. In this system, the data acquired during adsorption are fed back using a quartz crystal microbalance ŽQCM. to control the dipping time. Thus, high-quality self-assembled films were produced, because the thickness of each adsorbing layer was systematically controlled with nm-scale accuracy. We call this new type of polymer thin film a mass-controlled layer-by-layer self-assembly film w3᎐6x. The advantage of this type of film is that the microstructure and the mass ratio of polycationrpolyanion can be systematically controlled. A schematic image to show the structure of the new filter developed using the layer-by-layer sequential adsorption of polyelectrolytes in this study is shown in Fig. 1. The permeation characteristics of smoke or toxic gas into the filter are predicted to be high, because the film is very porous. Smoke or toxic gas is adsorbed by the film due to coulombic force and to the chemical reaction between the polymer and the toxic gas. Therefore, the air containing toxic gas will be cleaned after passing through the film. In this study, the following polymers were used for the deposition of layer-by-layer sequential adsorbed films: polyŽallylamine hydrochloride. ŽPAH. as polycation and polyŽacrylic acid. ŽPAA. as polyanion. For the
Fig. 1. Schematic illustration of the mechanism of the gas-adsorption image using a layer-by-layer self-assembly film.
Fig. 2. Experimental set-up to measure the filter performance.
deposition of film using the polyelectrolyte solutions, the pH of each solution was adjusted with NaOH or HCl solution. Up to 100 bilayers of the layer-by-layer sequentially adsorbed films were deposited on the surface of fiberglass cloths. The diameter of the fiber was 6 m. After deposition, the cloths were dried at 90⬚C in an oven. The performance of the filter was evaluated using static and gas-flow systems. For the static system, the top of an open vessel was covered by a filter sheet and the whole assembly was enclosed in a vinyl bag. The gas permeated through the filter was evaluated by measuring the gas concentration in the vinyl bag Žoutside of the vessel.. The experimental set-up of the gas flow system is shown in Fig. 2. As shown in Fig. 2, the concentration of the gas before and after passing through the filter was measured and compared. Ammonia and acetaldehyde were used as toxic gases for evaluation of the filter performance. The proof-reading gas was generated by the permeator, as shown in Fig. 3. This equipment produces a standard gas flow with constant concentration. Measurement of the gas concentration before and after passing through the filter was evaluated with gas detector tubes ŽGastec no. 91, 91L, 91LL, 91P, 91PL, 3L, 3M and 3LA.. The decrease in toxic gas concentration in the closed chamber was examined for the novel polyelectrolyte chemical filter. The surface structure of the layer-by-layer self assembly film was observed using an atomic force microscope ŽAFM. and a field-emission scanning electron microscope ŽFESEM..
Fig. 3. Gas proof-reading device.
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3. Results and discussions First, the performance of the filter was evaluated in a static system. The filter performance for the adsorption of ammonia or acetaldehyde is shown in Fig. 4. The figure shows the number of bilayers of the film vs. gas concentration after passing through filter. As the number of bilayers increases, the adsorption characteristics of the filters for ammonia gas improved. As shown in the figure, the filter fabricated with 100 bilayers removed 96% of the ammonia gas. Similar results were obtained for the case of acetaldehyde gas, although the removal ratio was 76%. The result measured by the ammonia gas-flow system is shown in Fig. 5. Similar results were obtained with the static system. The concentration of ammonia after passing through the filter decreased as the number of bilayers increased. A similar result was obtained for acetaldehyde. The adsorption mechanism of the coated polyelectrolytes was investigated using IR absorbance spectroscopy. Absorbance spectra of PAA films withrwithout exposure to ammonia are shown in Fig. 6a. Peaks corresponding to amide are shown in the range 1580᎐1680 cmy1 . One of the largest peaks in the spectrum, which was not observed for PAA cast film, was observed at 1650 cmy1 in the film after exposure to an ammonia atmosphere. Absorbance spectra of PAH cast films withrwithout exposure to an acetaldehyde atmosphere are shown in Fig. 6b. Maximum absorbance was observed in the range 1600᎐1680 cmy1 . In this study, a peak, which was not observed for PAH cast film, was clearly observed at 1570 cmy1 in the
Fig. 4. Change in the adsorption characteristics of ammonia and acetaldehyde gas with increasing number of bilayers in the static system.
Fig. 5. Ammonia adsorption effect of the fabricated filter in the gas flow system.
PAH film after exposure to an acetaldehyde atmosphere. Therefore, it was considered that ammonia is chemically adsorbed by PAA layers and acetaldehyde by PAH layers. The possible reactions are shown in the following. Ammonia gas reacts with carboxyl groups and amide is generated. The reaction is shown by formula Ža..
Acetaldehyde gas reacts with primary amine groups. The reaction is shown as formula Žb..
A comparison of the acetaldehyde adsorbance efficiency of the PAH cast film with active carbon is shown in Fig. 7. For this examination, the same mass of the PAH cast film and active carbon were compared, with both prepared on slide glasses. As shown in this figure, the adsorption efficiency of the PAH cast film was better than that of active carbon before annealing. In the case of active carbon, reemission of adsorbed gas molecules was often observed, because the adsorption of gas molecules was caused by physical adsorption. On the other hand, in the case of PAH films, reemission of adsorbed gas molecules was seldom observed, because the gas molecules were chemically adsorbed by the films. In a previous study, we reported that the nano-structure of the layer-by-layer self-assembled films changes according to the solution pH of the adsorbing bath w1,2x. To examine the relationship between the microscopic structure of the polyelectrolyte thin film and the
246
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Fig. 6. Ža. FTIR absorbance spectra of PAA cast films before and after exposure to ammonia atmosphere. Žb. FTIR absorbance spectra of PAH cast films before and after exposure to acetaldehyde atmosphere.
gas adsorption characteristics, the response characteristics to different concentrations of ammonia gas were studied using the quartz crystal microbalance ŽQCM. technique. Different types of nano-structures were formed by changing the solution pH of the polyelectrolytes w2x. The results are shown in Fig. 8. Fig. 8a shows the case when the polyelectrolyte film was deposited at pH 5.0 for PAH and pH 5.0 for PAA, and Fig. 8b the case when the polyelectrolyte film was deposited at pH 7.5 for PAH and pH 3.5 for PAA. As shown in the figure, the adsorption characteristics of the former are lower than the latter. In order to examine the surface structure of the
films, the surfaces were observed by atomic force microscopy ŽAFM.. The images are shown in Fig. 9a,b. In Fig. 9a, the film formed has a looped, porous structure, and in Fig. 9b, the polyelectrolyte films has a textile-like structure. RMS measurement of the surface roughness gave approximately 2 nm for Fig. 9a and 30 nm for Fig. 9b. We consider that the differences in gas adsorption characteristics were caused by the difference in the surface arearvolume ratio of the polyelectrolyte films. FESEM images of the bare cloth and the fiberglass cloth coated with the layer-by-layer self-assembly films are shown in Fig. 10a,b, respectively. As shown in the figure, the surface of the fiberglass cloth was uniformly
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Fig. 7. Comparison of the acetaldehyde absorption efficiency between PAH film and conventional active carbon.
coated by the self-assembled film, with nm-scale pores. These nano-pores were found to be extremely effective in improving the adsorption characteristics of the filter for toxic gas. Increasing the surface area and optimization of the materials and deposition conditions is in progress for the practical production of high-quality filters for removing various toxic gases. 4. Conclusions We have demonstrated the high performance of a polymer thin film, prepared by the layer-by-layer adsorption technique of polyelectrolytes films, as a filter for toxic gases, such as ammonia or acetaldehyde. The adsorption characteristics of the filter membrane for the toxic gas can be optimized by changing the deposi-
Fig. 9. AFM images of Ža. loopy; and Žb. textile structure Žboth 10 = 10 m2 ..
tion condition, such as pH of the adsorption solution, or the number of bilayers in the films. Consequently, these thin polymer films can be used as a new type of high-performance filter for air cleaning, which has remarkable adsorption characteristics for various toxic gases. Acknowledgements
Fig. 8. Difference in the adsorption characteristics for ammonia caused by the nano-structure of the thin film. Ža. PAH ŽpH 5.0.rPAA ŽpH 5.0.; and Žb. PAH ŽpH 7.5.rPAAŽpH 3.5..
A part of this work was supported by the Nippon Sheet Glass Foundation for Materials Science and Engineering Ž2000., the Mitsubishi Foundation Ž2000., and the Japan Science and Technology Corporation ŽJST.. The fiberglass cloth was supplied by Mie Textile Corporation, Japan. We thank Prof Rubner of the Massachusetts Institute of Technology for his advice on
S. Shiratori et al. r Thin Solid Films 393 (2001) 243᎐248
248
Fig. 10. FESEM images of the bare fiberglass cloth and the fiberglass cloth coated with the layer-by-layer self-assembled film.
the layer-by-layer self-assembly technique. We also acknowledge Mr Takeaki Kitamura of Mie Textile Corporation for offering the various fiberglass textiles and for his advice on the fiberglass cloths. References w1x D. Yoo, S.S. Shiratori, M.F. Rubner, Macromolecules 31 Ž1998. 4309.
w2x S. Shiratori, M.F. Rubner, Macromolecules 33 Ž2000. 4213. w3x Japanese patent application, no. 10-10-267286r1998, 11-077553, 11-077554. w4x S.S. Shiratori, M. Yamada, Polym. Adv. Technol. 11 Ž2000. 810. w5x S.S. Siratori, Y. Inami, M. Kikuchi, Trans. Mater. Res. Soc. Jpn. 25 Ž2. Ž2000. 401. w6x S.S. Shiratori, Y. Inami, M. Kichiku, M. Yamada, T. Yamada, Polym. Adv. Technol. 11 Ž2000. 766.