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FT NIR Raman studies of alginic acid–benzimidazole polymer composite
Spectrochimica Acta Part A 79 (2011) 797–800
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
FT NIR Raman studies of alginic acid–benzimidazole polymer composite M. Połomska a,∗ , K. Pogorzelec-Glaser a , C. Pawlaczyk a , A. Pietraszko b a b
Institute of Molecular Physics, Polish Academy of Sciences, Pozna´ n, Poland Institute of Low Temperatures and Structure Research, Polish Academy of Sciences, Wrocław, Poland
a r t i c l e
i n f o
Article history: Received 31 October 2009 Accepted 26 August 2010 Keywords: Biodegradable anhydrous polymer electrolyte Alginic acid Benzimidazole Electric conductivity
a b s t r a c t New bio-inspired polymer composites of alginic acid and benzimidazole were created and characterized by FT NIR Raman spectroscopy. The obtained films with 1:0.5, 1:1 and 1:1.5 molar ratio are homogeneous, with good mechanical properties. Raman spectra recorded at room temperature revealed that the obtained films are a new compound with a different molecular structure and physical properties compared with pure substrates: alginic acid and benzimidazole. Raman band related to vibration of COOH entity at 1740 cm−1 of alginic acid disappears in the alginic acid:benzimidazole composites, in which new Raman band related to COO− was found. Additionally, characteristic lines observed in polymer composites which may be associated with vibrations of NH groups, can be attributed to the linking of proton to deprotonated N atom in benzimidazole group. Possibility of such proton exchange is a promising property which might facilitate the application of obtained composites to anhydrous proton conducting electrolytes in fuel cells. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Interest in energy conversion systems, e.g. polymer fuel cells, where polymer electrolytes are essential, stimulates the search of an appropriate polymer membrane, which acts both as an electrolyte medium for proton transport and as fuel and oxygen separator. Proton transport in commonly used perfluorinated ionomers (Nafion® , Dow® membranes) [1], as well as in polymers based on sulfonated polyetherketones [2] and organic/inorganic nanocomposites membranes [3] is related to hydration in the membrane and therefore limited to temperatures below the water boiling point. The low operation temperature of the membranes results in catalyst poisoning by CO and complicates the water management increasing the operation expenses, independently of sufficiently high production costs [4]. An approach to make the polymer electrolyte membrane technically and economically competitive is to use water-free electrolyte systems with high proton conductivity at high temperatures. Kreuer and coworkers proposed nitrogen containing heterocycles (imidazole and pyrazole) as proton solvents in polymer electrolyte membranes due to their amphoteric nature, the formation of intermolecular hydrogen bonds, and the ability of undergoing self-dissociation [5–8]. The synthesis of heterocyclic molecules with biopolymers appears to be an extremely interesting proposal for PEFC. Very recently studies, of new proton conducting polymer electrolyte networks consisting of alginate acid (AA) and heterocyclic molecules
such as imidazole and 1H-1,2,4-triazole [9–11] were prepared. The conductivity value, temperature range of work (100–200 ◦ C) and mechanical properties of the obtained materials suggest that these materials are potential candidates for fuel cell membranes. Presented paper describes the preparation and study of a new anhydrous polymer composite consisting of alginate acid and benzimidazole. Alginic acid (AA), one of the elements of marine algae, is a natural polysaccharide containing linear chains of 1,4 linked -dmannuronic acid (M) and ␣-l-guluronic acid (G). The linear chains of M- and G-type acids are covalently linked together to different sequences or blocks. AA is a biodegradable, biocompatible, nontoxic and low-cost polymer. Benzimidazole belongs to aromatic heterocyclic molecules, where the atoms with or without protons may act as donors and acceptors, respectively, in the reaction of proton transport. The main aim of our work was to study by means of Raman spectroscopy and characterize new polymer composites obtained using alginate acid with heterocyclic benzimidazole molecule. Raman spectroscopy is an extremely useful tool which provides detailed information of the material and its structure of the molecular level. It can be a source of additional information on ion exchange in AA:BnIm polymer material. 2. Experimental 2.1. Materials
∗ Corresponding author. E-mail address: [email protected] (M. Połomska). 1386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2010.08.055
Commercial alginic acid (AA) containing ∼61% mannuroic acid and ∼39% guluronic acid from Sigma and benzimidazole (BnIm)
798
M. Połomska et al. / Spectrochimica Acta Part A 79 (2011) 797–800
from Fluka were used in alginic acid–benzimidazole (AA:BnIm) thin films preparation. AA:BnIm films were prepared with three different molar compositions 1:0.5; 1:1; 1:1.5 in the following way: a mixture of AA and water solution of BnIm was stirred for ∼24 h to obtain a homogeneous mixture in the form of gel. The gel was cast on glass or Teflon plates and dried for ∼24 h at 60 ◦ C. 30–90 m thick, homogeneous, transparent films of AA-BnIm polymer composite were obtained. The concentration of AA:BnIm of 1:1.5 appeared to be the highest for which proper homogeneous films could be obtained. 2.2. FT NIR Raman scattering measurements FT NIR Raman spectra of the polymer films of AA:BnIm composite were recorded using Bruker IFS66FRA106 spectrometer. The samples were excited with a 1064 nm diode-pumped Nd:YAG laser of output power ∼30 mW. Raman studies at room temperature were carried out at 180◦ geometry and recorded in the 100–3500 cm−1 frequency range, collected with 1000 scans and 4 cm−1 spectral resolution. 3. Results and discussion To answer the question about the kind of compound obtained during the preparation of polymer AA:BnIm films we studied the Raman spectra of the substrate, i.e. the alginic acid, benzimidazole and the films obtained in accordance with the procedure described earlier. Discussing our results we will focus on the most significant changes observed for AA:BnIm polymer films compared to the substrates. Fig. 1 presents the Raman spectra of the pure alginic acid, benzimidazole and the spectrum of the AA:BnIm film obtained for the molar ratio of 1:1. In Fig. 2 the Raman spectra of AA:BnIm polymer composition for different content of BnIm are presented. The comparison of these spectra reveals that in the Raman spectra of AA:BnIm films we can find the bands which are different from those of alginic acid and benzimidazole. Generally the bands of AA:BnIm polymer composite are broader in comparison to pure AA and BnIm. XRD studies revealed that benzimidazole molecules are embedded into alginic acids chains. Moreover the studies revealed that AA:BnIm are characterized by high content of amorphic phase. Detailed results of XRD studies will be published in the other paper. To determine the assignments of the Raman bands of AA:BnIm polymer composite we used results both Raman and IR studies of, e.g. different sodium alginates [12,13] alginates [14], alginate hydrogels [15] and experimental Raman and theoretical studies of benzimidazole [16–19]. In the frequency range 200–980 cm −1 (Figs. 1a and 2a) the bands of AA:BnIm composite appear mostly at similar frequencies at which lines characteristic both for AA and BnIm can be found. However the line centered at ∼623 cm−1 for BnIm assigned to out-of-plane NH bending vibrations [17,18] in AA:BnIm gets narrower and more intense. The intensity of the band increases with BnIm content in the polymer composite. Such behaviour may indicate on proton exchange between the COOH group of AA and non-protonated nitrogen atom in benzimidazole. Compared to pure AA and BnIm the most significant changes in the film were found in 1000–1800 cm−1 frequency range. For example instead of a line centered at ∼1401 cm−1 of AA assigned to the deformation vibrations: ␦CH2 , ␦(HCC),␦(HCO), ␦(COH) [15] and doublet of lines at 1410 and 1420 cm−1 of BnIm assigned among others to XH and CH in-plane vibrations and NH vibration related to imidazole group of BnIm, in the AA:BnIm polymer composite we observe very broad band centered at ∼1416 cm−1 . The intensity of the line increases with the increase of BnIm content in the AA:BnIm polymer. A new line which appears at ∼1450 cm−1 may be
Fig. 1. Raman spectra of benzimidazole (1), alginic acid–benzimidazole complex with molar ratio of 1:1 (2) and alginic acid (3) measured at room temperature.
assigned to the vibration of the COO− entity resulting from deprotonating of AA. Similar behaviour was reported in IR studies of alginic acid components with other heterocyclic molecules [9,11]. Further changes can be observed for the bands at the 1587 and 1619 cm−1 frequencies characteristic of benzimidazole and attributed to the bending vibrations of CH, NH and bending vibrations of XH and CC, respectively [17]. The ratio of relative intensity of these two
M. Połomska et al. / Spectrochimica Acta Part A 79 (2011) 797–800
Fig. 3. Temperature dependence of dc electric conductivity acid–benzimidazole complex for different content of benzimidazole.
799
of
alginic
Raman bands in AA:BnIm polymer I1587 /I1619 varies depending on the content of benzimidazole—from 0.45 for 1:0.5 molar ratio of AA:BnIm to 1.67 for 1:1.5. For comparison I1580 /I1620 for benzimidazole equals 4.98. The band in the Raman spectrum of alginic acid whose location corresponds to ∼1733 cm−1 is related to vibrations of the COOH group [12,13]. As one can notice in Figs. 1b and 2b, the intensity of this band decreases significantly for AA:BnIm polymer with the composition of 1:0.5 and it disappears completely for higher concentrations of BnIm in AA. This means that for the concentrations higher than 1:0.5 the COOH group was deprotonated completely in AA:BnIm. This explains the increased intensity of the line at ∼1587 cm−1 in AA:BnIm related, among others, to the bending vibrations of NH− the proton from COOH group is bending to free N atom in benzimidazole. In Figs. 1c and 2c the region of 2800–3500 cm−1 of the Raman spectra corresponding to CH stretching vibration is presented. The lines at ∼3066, 3092 and 3114 cm−1 assigned to CH vibrations of BnIm (Fig. 1c) undergo significant broadening to practically one broad band centered at ∼3070 cm−1 with shoulder at ∼3112 cm−1 for polymer with 1:1.5 molar ratio of AA:BnIm (Fig. 2c). The broadening of the band may indicate on very strong intermolecular aggregation within polymer composite. The broad line at ∼2934 cm−1 assigned to CH vibration of AA shifts into lower frequency of ∼2918 cm−1 for 1:1.5 molar ratio of AA:BnIm and also gets more broad.
4. Conclusions
Fig. 2. Raman spectra of alginic acid–benzimidazole complex for different content of benzimidazole measured at room temperature.
The aim of our work was to study recently obtained composite of alginic acid biopolymer and benzimidazole, which are anhydrous proton conductors. Raman spectroscopy allows to detect any changes which arise in the molecular structure of the studied materials. The results of Raman studies presented in this paper indicate that the new polymer composite exhibit the spectra whose bands are related to a new compound benzimidazole and alginic acid complex. The obtained AA:BnIm films are characterized by good mechanical properties and relatively high proton conductivity of the order of 10−4 S/m at 130 ◦ C. In Fig. 3 the results of temperature measurements of electrical conductivity with using impedance spectroscopy are shown. These materials can therefore be regarded as a candidates for membranes in fuel cells. Detailed studies of thermal and electrical properties of these materials will be published soon.
800
M. Połomska et al. / Spectrochimica Acta Part A 79 (2011) 797–800
Acknowledgement This work was supported by the funds for science in years 2007–2010 as a research project N N507 3852 33. References [1] [2] [3] [4] [5]
J.A. Kerres, J. Membr. Sci. 185 (2001) 1. K.D. Kreuer, J. Membr. Sci. 185 (2001) 29. I. Honma, S. Nomura, H. Nakajima, J. Membr. Sci. 185 (2001) 83. Q. Li, R. He, J.O. Jensen, N.J. Bjerrum, Chem. Mater. 15 (2003) 4896. K.D. Kreuer, A. Fuchs, M. Ise, M. Spaeth, J. Maier, Electrochim. Acta 43 (1998) 1281. [6] M. Schuster, W.H. Meyer, G. Wegner, H.G. Herz, M. Ise, M. Schuster, K.D. Kreuer, J. Maier, Solid State Ionics 145 (2001) 85.
[7] H.G. Herz, K.D. Kreuer, J. Maier, G. Scharfenberger, M.F.H. Schuster, W.H. Meyer, Electrochim. Acta 48 (2003) 2165. [8] M.F.H. Schuster, W.H. Meyer, M. Schuster, K.D. Kreuer, Chem. Mater. 16 (2004) 329. [9] M. Yamada, I. Honma, Polymer 45 (2004) 8349. [10] I. Honma, M. Yamada, Bull. Chem. Soc. Jpn. 80 (2007) 2110. [11] S.T. Gunday, A. Bozkurt, Polym. J. 40 (2008) 104. [12] C. Sartori, D.F. Finch, B. Ralph, K. Gilding, Polymer 1 (1997) 43. [13] J.P. Soares, J.E. Santos, G.O. Chierice, E.T.G. Cavalheiro, Eclectica 29 (2004) 57. [14] L. Pereira, A. Sousa, H. Coelho, A.M. Amado, P.J.A. Ribeiro-Claro, Biomol. Eng. 20 (2003) 223. [15] A. Pielesz, Fibres Textiles East. Eur. 15 (2007) 136. [16] T.D. Klots, P. Devlin, W.B. Collier, Spectrochim. Acta Part A 53 (1997) 2445. [17] M.A. Morsy, A.A. Al-Khaldi, A. Suwaiyan, J. Phys. Chem. A 106 (2002) 9196. [18] N. Sundaraganesan, S. Ilakiamani, P. Subramani, B. Dominic Joshua, Spectrochim. Acta Part A 67 (2007) 628. [19] J. Tomkinson, J. Phys. Chem. A 112 (2008) 6115.
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
FT NIR Raman studies of alginic acid–benzimidazole polymer composite M. Połomska a,∗ , K. Pogorzelec-Glaser a , C. Pawlaczyk a , A. Pietraszko b a b
Institute of Molecular Physics, Polish Academy of Sciences, Pozna´ n, Poland Institute of Low Temperatures and Structure Research, Polish Academy of Sciences, Wrocław, Poland
a r t i c l e
i n f o
Article history: Received 31 October 2009 Accepted 26 August 2010 Keywords: Biodegradable anhydrous polymer electrolyte Alginic acid Benzimidazole Electric conductivity
a b s t r a c t New bio-inspired polymer composites of alginic acid and benzimidazole were created and characterized by FT NIR Raman spectroscopy. The obtained films with 1:0.5, 1:1 and 1:1.5 molar ratio are homogeneous, with good mechanical properties. Raman spectra recorded at room temperature revealed that the obtained films are a new compound with a different molecular structure and physical properties compared with pure substrates: alginic acid and benzimidazole. Raman band related to vibration of COOH entity at 1740 cm−1 of alginic acid disappears in the alginic acid:benzimidazole composites, in which new Raman band related to COO− was found. Additionally, characteristic lines observed in polymer composites which may be associated with vibrations of NH groups, can be attributed to the linking of proton to deprotonated N atom in benzimidazole group. Possibility of such proton exchange is a promising property which might facilitate the application of obtained composites to anhydrous proton conducting electrolytes in fuel cells. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Interest in energy conversion systems, e.g. polymer fuel cells, where polymer electrolytes are essential, stimulates the search of an appropriate polymer membrane, which acts both as an electrolyte medium for proton transport and as fuel and oxygen separator. Proton transport in commonly used perfluorinated ionomers (Nafion® , Dow® membranes) [1], as well as in polymers based on sulfonated polyetherketones [2] and organic/inorganic nanocomposites membranes [3] is related to hydration in the membrane and therefore limited to temperatures below the water boiling point. The low operation temperature of the membranes results in catalyst poisoning by CO and complicates the water management increasing the operation expenses, independently of sufficiently high production costs [4]. An approach to make the polymer electrolyte membrane technically and economically competitive is to use water-free electrolyte systems with high proton conductivity at high temperatures. Kreuer and coworkers proposed nitrogen containing heterocycles (imidazole and pyrazole) as proton solvents in polymer electrolyte membranes due to their amphoteric nature, the formation of intermolecular hydrogen bonds, and the ability of undergoing self-dissociation [5–8]. The synthesis of heterocyclic molecules with biopolymers appears to be an extremely interesting proposal for PEFC. Very recently studies, of new proton conducting polymer electrolyte networks consisting of alginate acid (AA) and heterocyclic molecules
such as imidazole and 1H-1,2,4-triazole [9–11] were prepared. The conductivity value, temperature range of work (100–200 ◦ C) and mechanical properties of the obtained materials suggest that these materials are potential candidates for fuel cell membranes. Presented paper describes the preparation and study of a new anhydrous polymer composite consisting of alginate acid and benzimidazole. Alginic acid (AA), one of the elements of marine algae, is a natural polysaccharide containing linear chains of 1,4 linked -dmannuronic acid (M) and ␣-l-guluronic acid (G). The linear chains of M- and G-type acids are covalently linked together to different sequences or blocks. AA is a biodegradable, biocompatible, nontoxic and low-cost polymer. Benzimidazole belongs to aromatic heterocyclic molecules, where the atoms with or without protons may act as donors and acceptors, respectively, in the reaction of proton transport. The main aim of our work was to study by means of Raman spectroscopy and characterize new polymer composites obtained using alginate acid with heterocyclic benzimidazole molecule. Raman spectroscopy is an extremely useful tool which provides detailed information of the material and its structure of the molecular level. It can be a source of additional information on ion exchange in AA:BnIm polymer material. 2. Experimental 2.1. Materials
∗ Corresponding author. E-mail address: [email protected] (M. Połomska). 1386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2010.08.055
Commercial alginic acid (AA) containing ∼61% mannuroic acid and ∼39% guluronic acid from Sigma and benzimidazole (BnIm)
798
M. Połomska et al. / Spectrochimica Acta Part A 79 (2011) 797–800
from Fluka were used in alginic acid–benzimidazole (AA:BnIm) thin films preparation. AA:BnIm films were prepared with three different molar compositions 1:0.5; 1:1; 1:1.5 in the following way: a mixture of AA and water solution of BnIm was stirred for ∼24 h to obtain a homogeneous mixture in the form of gel. The gel was cast on glass or Teflon plates and dried for ∼24 h at 60 ◦ C. 30–90 m thick, homogeneous, transparent films of AA-BnIm polymer composite were obtained. The concentration of AA:BnIm of 1:1.5 appeared to be the highest for which proper homogeneous films could be obtained. 2.2. FT NIR Raman scattering measurements FT NIR Raman spectra of the polymer films of AA:BnIm composite were recorded using Bruker IFS66FRA106 spectrometer. The samples were excited with a 1064 nm diode-pumped Nd:YAG laser of output power ∼30 mW. Raman studies at room temperature were carried out at 180◦ geometry and recorded in the 100–3500 cm−1 frequency range, collected with 1000 scans and 4 cm−1 spectral resolution. 3. Results and discussion To answer the question about the kind of compound obtained during the preparation of polymer AA:BnIm films we studied the Raman spectra of the substrate, i.e. the alginic acid, benzimidazole and the films obtained in accordance with the procedure described earlier. Discussing our results we will focus on the most significant changes observed for AA:BnIm polymer films compared to the substrates. Fig. 1 presents the Raman spectra of the pure alginic acid, benzimidazole and the spectrum of the AA:BnIm film obtained for the molar ratio of 1:1. In Fig. 2 the Raman spectra of AA:BnIm polymer composition for different content of BnIm are presented. The comparison of these spectra reveals that in the Raman spectra of AA:BnIm films we can find the bands which are different from those of alginic acid and benzimidazole. Generally the bands of AA:BnIm polymer composite are broader in comparison to pure AA and BnIm. XRD studies revealed that benzimidazole molecules are embedded into alginic acids chains. Moreover the studies revealed that AA:BnIm are characterized by high content of amorphic phase. Detailed results of XRD studies will be published in the other paper. To determine the assignments of the Raman bands of AA:BnIm polymer composite we used results both Raman and IR studies of, e.g. different sodium alginates [12,13] alginates [14], alginate hydrogels [15] and experimental Raman and theoretical studies of benzimidazole [16–19]. In the frequency range 200–980 cm −1 (Figs. 1a and 2a) the bands of AA:BnIm composite appear mostly at similar frequencies at which lines characteristic both for AA and BnIm can be found. However the line centered at ∼623 cm−1 for BnIm assigned to out-of-plane NH bending vibrations [17,18] in AA:BnIm gets narrower and more intense. The intensity of the band increases with BnIm content in the polymer composite. Such behaviour may indicate on proton exchange between the COOH group of AA and non-protonated nitrogen atom in benzimidazole. Compared to pure AA and BnIm the most significant changes in the film were found in 1000–1800 cm−1 frequency range. For example instead of a line centered at ∼1401 cm−1 of AA assigned to the deformation vibrations: ␦CH2 , ␦(HCC),␦(HCO), ␦(COH) [15] and doublet of lines at 1410 and 1420 cm−1 of BnIm assigned among others to XH and CH in-plane vibrations and NH vibration related to imidazole group of BnIm, in the AA:BnIm polymer composite we observe very broad band centered at ∼1416 cm−1 . The intensity of the line increases with the increase of BnIm content in the AA:BnIm polymer. A new line which appears at ∼1450 cm−1 may be
Fig. 1. Raman spectra of benzimidazole (1), alginic acid–benzimidazole complex with molar ratio of 1:1 (2) and alginic acid (3) measured at room temperature.
assigned to the vibration of the COO− entity resulting from deprotonating of AA. Similar behaviour was reported in IR studies of alginic acid components with other heterocyclic molecules [9,11]. Further changes can be observed for the bands at the 1587 and 1619 cm−1 frequencies characteristic of benzimidazole and attributed to the bending vibrations of CH, NH and bending vibrations of XH and CC, respectively [17]. The ratio of relative intensity of these two
M. Połomska et al. / Spectrochimica Acta Part A 79 (2011) 797–800
Fig. 3. Temperature dependence of dc electric conductivity acid–benzimidazole complex for different content of benzimidazole.
799
of
alginic
Raman bands in AA:BnIm polymer I1587 /I1619 varies depending on the content of benzimidazole—from 0.45 for 1:0.5 molar ratio of AA:BnIm to 1.67 for 1:1.5. For comparison I1580 /I1620 for benzimidazole equals 4.98. The band in the Raman spectrum of alginic acid whose location corresponds to ∼1733 cm−1 is related to vibrations of the COOH group [12,13]. As one can notice in Figs. 1b and 2b, the intensity of this band decreases significantly for AA:BnIm polymer with the composition of 1:0.5 and it disappears completely for higher concentrations of BnIm in AA. This means that for the concentrations higher than 1:0.5 the COOH group was deprotonated completely in AA:BnIm. This explains the increased intensity of the line at ∼1587 cm−1 in AA:BnIm related, among others, to the bending vibrations of NH− the proton from COOH group is bending to free N atom in benzimidazole. In Figs. 1c and 2c the region of 2800–3500 cm−1 of the Raman spectra corresponding to CH stretching vibration is presented. The lines at ∼3066, 3092 and 3114 cm−1 assigned to CH vibrations of BnIm (Fig. 1c) undergo significant broadening to practically one broad band centered at ∼3070 cm−1 with shoulder at ∼3112 cm−1 for polymer with 1:1.5 molar ratio of AA:BnIm (Fig. 2c). The broadening of the band may indicate on very strong intermolecular aggregation within polymer composite. The broad line at ∼2934 cm−1 assigned to CH vibration of AA shifts into lower frequency of ∼2918 cm−1 for 1:1.5 molar ratio of AA:BnIm and also gets more broad.
4. Conclusions
Fig. 2. Raman spectra of alginic acid–benzimidazole complex for different content of benzimidazole measured at room temperature.
The aim of our work was to study recently obtained composite of alginic acid biopolymer and benzimidazole, which are anhydrous proton conductors. Raman spectroscopy allows to detect any changes which arise in the molecular structure of the studied materials. The results of Raman studies presented in this paper indicate that the new polymer composite exhibit the spectra whose bands are related to a new compound benzimidazole and alginic acid complex. The obtained AA:BnIm films are characterized by good mechanical properties and relatively high proton conductivity of the order of 10−4 S/m at 130 ◦ C. In Fig. 3 the results of temperature measurements of electrical conductivity with using impedance spectroscopy are shown. These materials can therefore be regarded as a candidates for membranes in fuel cells. Detailed studies of thermal and electrical properties of these materials will be published soon.
800
M. Połomska et al. / Spectrochimica Acta Part A 79 (2011) 797–800
Acknowledgement This work was supported by the funds for science in years 2007–2010 as a research project N N507 3852 33. References [1] [2] [3] [4] [5]
J.A. Kerres, J. Membr. Sci. 185 (2001) 1. K.D. Kreuer, J. Membr. Sci. 185 (2001) 29. I. Honma, S. Nomura, H. Nakajima, J. Membr. Sci. 185 (2001) 83. Q. Li, R. He, J.O. Jensen, N.J. Bjerrum, Chem. Mater. 15 (2003) 4896. K.D. Kreuer, A. Fuchs, M. Ise, M. Spaeth, J. Maier, Electrochim. Acta 43 (1998) 1281. [6] M. Schuster, W.H. Meyer, G. Wegner, H.G. Herz, M. Ise, M. Schuster, K.D. Kreuer, J. Maier, Solid State Ionics 145 (2001) 85.
[7] H.G. Herz, K.D. Kreuer, J. Maier, G. Scharfenberger, M.F.H. Schuster, W.H. Meyer, Electrochim. Acta 48 (2003) 2165. [8] M.F.H. Schuster, W.H. Meyer, M. Schuster, K.D. Kreuer, Chem. Mater. 16 (2004) 329. [9] M. Yamada, I. Honma, Polymer 45 (2004) 8349. [10] I. Honma, M. Yamada, Bull. Chem. Soc. Jpn. 80 (2007) 2110. [11] S.T. Gunday, A. Bozkurt, Polym. J. 40 (2008) 104. [12] C. Sartori, D.F. Finch, B. Ralph, K. Gilding, Polymer 1 (1997) 43. [13] J.P. Soares, J.E. Santos, G.O. Chierice, E.T.G. Cavalheiro, Eclectica 29 (2004) 57. [14] L. Pereira, A. Sousa, H. Coelho, A.M. Amado, P.J.A. Ribeiro-Claro, Biomol. Eng. 20 (2003) 223. [15] A. Pielesz, Fibres Textiles East. Eur. 15 (2007) 136. [16] T.D. Klots, P. Devlin, W.B. Collier, Spectrochim. Acta Part A 53 (1997) 2445. [17] M.A. Morsy, A.A. Al-Khaldi, A. Suwaiyan, J. Phys. Chem. A 106 (2002) 9196. [18] N. Sundaraganesan, S. Ilakiamani, P. Subramani, B. Dominic Joshua, Spectrochim. Acta Part A 67 (2007) 628. [19] J. Tomkinson, J. Phys. Chem. A 112 (2008) 6115.