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sulfonated polycarbonate blends
Synthetic Metals 113 Ž2000. 237–243 www.elsevier.comrlocatersynmet
Electrical properties of polyanilinersulfonated polycarbonate blends Wan-Jin Lee ) , Yong-Ju Kim, Shinyoung Kaang Faculty of Applied Chemistry, College of Engineering, Chonnam National UniÕersity, 300 Yongbong-dong, Puk-gu, Kwangju 500-757, South Korea Received 4 August 1999; received in revised form 1 December 1999; accepted 7 February 2000
Abstract A conducting composite using polyaniline ŽPANI. as the conducting polymer and polycarbonate ŽPC. as a matrix was prepared by a blending method. Chloroform was used as a solvent in the blending. The PANI was protonated using camphor sulfonic acid ŽCSA. or a dodecylbenzene sulfonic acid ŽDBSA. such as alkylbenzenesulfonic acid. A sulfonic group was introduced into the structure of the PC in order to enhance the coulombic interaction between each phase of the composite. The effect of ionic groups in sulfonated PC ŽSPC. was monitored using measurements of both the mechanical and thermal properties. Using the presence of protonating agents and the amount of PANI complex, both the electrical conductivity and morphology were measured. Electrical conductivity increased to 7.5 Srcm with the amount of PANI complex protonated with DBSA having a long alkyl chain. q 2000 Elsevier Science S.A. All rights reserved. Keywords: Polyaniline; Sulfonation; Polycarbonate; Blends
1. Introduction The development of polymers with high electrical conductivity has attracted significant research interest in the last decade due to the possibility of new applications w1–3x. There has also been progress in the processability of polythiophene and polypyrrole, as well as of polyaniline ŽPANI. w4–6x. One of the conducting polymers that has attracted considerable interest in the last few years is PANI. PANI seems to be one of the best candidates for the preparation of polymer-based conducting polymer composites. It is stable in a normal atmosphere, and recently, significant progress has been achieved in the preparation of processable forms of PANI w7,8x. Cao et al. w9,10x and Lee et al. w11x showed that PANI, protonated with camphor sulfonic acid ŽCSA. or dodecylbenzene sulfonic acid ŽDBSA., can be processed from solutions. A soluble PANI complex can be obtained through doping by CSA or DBSA because the molecular interfacial interaction is decreased. This means that the PANI complex doped by CSA or DBSA is ther-
) Corresponding author. Tel.: q82-62-530-1895; fax: q82-62-5301889. E-mail address: [email protected] ŽW.-J. Lee..
mally stable compared with the PANI complex doped by small molecules such as HCl. Recently, several conductive composites of protonated PANI with insulating polymer have been reported elsewhere w12–14x. However, the two phases are basically immiscible, and the phase separation is still to be found between each phase. If the miscibility of these blends were to be enhanced between phases, the electrical and mechanical properties would be increased. The morphology in immiscible blends is determined by various parameters, such as interfacial tension, volume fractions, and viscosity ratios w15x. Various methods to enhance properties in immiscible blends include using precursors, compatibilizers such as block copolymers, or introducing ionic polymers w16x. By introducing ionic groups such as a sulfonic group to the insulating polymer, such as polystyrene and polycarbonate ŽPC., it is possible to enhance the miscibility between two phases w17,18x. Therefore, this will minimize the phase separation between the conducting polymer and the insulating polymer. This would lead to an increase in the mechanical and electrical properties, due to an increase of the compatibility and the induction of electrostatic interaction. In this article, we report on the preparation of conductive, flexible composites of PANI and sulfonated PC ŽSPC.,
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and the effect of the introduction of ionic groups on the compatibility of the electrical and mechanical properties.
where Y represents the amount of consumed HCl, NNaOH is the normal concentration of NaOH, and NHCl is the normal concentration of HCl.
2. Experimental
2.6. Measurements of electrically conductiÕe polymer composites
2.1. Materials The PC was obtained from Sumitomo Žtype 201-15 resin, MW 22000, density 1.20, Tg 1508C., and was distilled under vacuum before use. The PANI emeraldine base was commercially purchased from Aldrich and was distilled under vacuum before use and stored in nitrogen. The CSA and DBSA used protonating agents that were purchased from Aldrich. The chloroform ŽJunsei Chemical., used as a solvent, and chlorosulfuric acid ŽKanto Chemical., used as a sulfonating agent, were used without purification. 2.2. Protonation of polyemeraldine base Two groups of protonating agents were used: CSA and DBSA. For the protonation reaction, a polyemeraldine base was mixed with the appropriate protonating agent in the molar ratio of wacid moleculesx:wPANI merx s 0.5. This mixture was then dissolved and vigorously stirred at 408C for 24 h, the time required to reach the maximum dissolution, and then centrifuged to remove minor solids. 2.3. Sulfonation of PC PC was dissolved to form a 10 wt.% solution in chloroform by mechanical mixing at room temperature. Then, chlorosulfuric acid in an additional four-neck flask under nitrogen gas was dropped slowly with vigorous stirring. The reaction was continued for 5 h. Sulfonated products were filtered, and washed with Na 2 CO 3 and methanol. Finally, the powder sample was obtained after dried SPC in a vacuum oven.
The conductivity of the sample in the plane direction was determined by a standard four-probe method. Infrared studies and UV–Vis absorption spectra of composite films were carried out on a Mattson 1000 FT-IR spectrometer and Hitachi U-3501 UV–Vis absorption spectrometer, respectively. NMR studies for structural analysis of SPC were carried out using a Varian Unity Plus-300 and 300 MHz proton nuclear magnetic resonance spectroscopy. Thermal gravimetric analysis ŽTGA. measurements were performed on a TA TGA7 instrument. The sample was cut to the size required by the ASTM D638. Tensile testing was performed using an Instron testing instrument ŽUniframe TC-55, Satec System. at room temperature with a load cell of 200 lb and cross-head speed of 3.0 mmrmin. Scanning electron micrographs of the electrical composite film were obtained with a Jeol JSM-5400 instrument.
3. Results and discussion 3.1. FT-IR analysis of SPC The results of the FT-IR and NMR of the original sample PC were compared with that of the SPC. As shown in Fig. 1, the typical peaks of SO 3 H are absorption at 1250–1150 and 1060–1030 cmy1 . The strong band of the frequency, 1250–1150 cmy1 , can be ascribed to stretch vibration for S5O, and the absorption band at the 1060– 1030 cmy1 is assigned to the symmetric stretching band. However, the stretching band of C5O is 1765–1720 cmy1 in the ester group for PC, while the C`O`C for asymmetric stretching band is 1290–1180 cmy1 , and the O`C`O peak is 645–575 cmy1 . The spectra were so complex that
2.4. Preparation of composite film The protonated PANI complex was mixed in an appropriate ratio with PC or SPC in chloroform. This mixture was cast on a glass substrate as film types of about 50-mm thickness, and then the solvent was evaporated in the vacuum oven at 708C. 2.5. The capacity of ion exchange of SPC The ion exchange capacity was measured by the Fisher’s back titration method w19x at room temperature according to the concentrations of chlorosulfuric acid. The ion exchange capacity was calculated by the following equation: the capacity of ion exchange Ž meqrg. s Ž 50 = NNaOH y Y = NHCl . rweight of polymer,
Fig. 1. FT-IR spectra of PC and SPC.
W.-J. Lee et al.r Synthetic Metals 113 (2000) 237–243
Fig. 2. NMR spectra of PC and SPC.
they could not easily be used, due to an overlap of the absorption of the sulfonic group and ester group of PC. So, the NMR analysis is shown in the following figure. 3.2. NMR analysis of SPC In Fig. 2, the 1 H NMR spectra of SPC and PC were compared. In the case of the PC, the symmetric peaks of the benzene rings appeared at 7.0–7.4 ppm. In the vicinity of 2 ppm, one peak of C`C`C structure is evident. In the case of SPC, a new peak of benzene ring at 6.7–7.2 ppm is made to appear by the disappearance of the symmetric structure in order to introduce the SO 3 H group to PC. Also, one peak of the C`C`C structure, about 2 ppm, is broken because the balance of the benzene ring in both sides was lost. Fig. 3 shows the chemical structure of synthesized SPC. The reactive substitution position is situated meta to the aryl ester linkage in the bisphenol unit. This position is the most favorable site because it is electrophilically activated by CH 3 , rather than by ester. 3.3. Ion exchange capacity of SPC Fig. 4 shows the change of the ion exchange capacity according to the concentration of chlorosulfuric acid when the PC was sulfonated. This sulfonation was carried out at
Fig. 3. Reaction scheme of SPC preparation.
239
Fig. 4. Relationship between sulfonation degrees and sulfonating agent contents.
258C for 5 h. The ion exchange capacity was measured by the Fisher’s back titration method. The ion exchange capacity increased with an increasing CSA concentration, but it did not increase more than 2 mol. It then reached its critical point at over 2.5 mol. In this study, the experiment was carried out at the condition of 2.5 mol. 3.4. Thermal property of SPC Fig. 5 shows the TGA of PC and SPC. In the case of SPC, the weight loss appeared in the vicinity of 1808C. This result can be explained by the fact that the sulfonic group introduced PC matrix decomposed due to the unstable structure of the SOy 3 group. The benzene ring of the PC matrix broke down in the vicinity of 2678C, possibly causing the weight loss. 3.5. Protonation of the PANI by CSA and DBSA Generally, a conducting polymer is not easily dissolved by common organic solvents, due to its large intermolecular interfacial tension. But, a soluble PANI complex can be obtained to dope by CSA or DBSA because the molecular
Fig. 5. TGA thermograms of PC and SPC.
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interfacial interaction is decreased. This means that the PANI complex, doped by CSA or DBSA, is more thermally stable compared to the PANI complex doped by small molecule like HCl. Fig. 6 shows the results of the FT-IR analysis to confirm the protonation of PANI doped by CSA or DBSA such as alkylbenzenesulfonic acid. Fig. 6Žb. shows the peaks of the PANI complex protonated by CSA in chloroform. The stretching band of S5O represents an absorption band of 1200 cmy1 , and C5O band of cyclohexanone is evident at 1600 cmy1 , because of the effect of ring strain. Fig. 6Žc. represents the peaks of PANI protonated by DBSA in chloroform. The C`H band of the aromatic ring becomes evident at 3000 cmy1 , and then the aliphatic peaks, such as –CH 3 and CH 2 by alkyl chain, can be observed at 2990–2850 cmy1 . Also, the stretching band of S5O represents an absorption band of 1200 cmy1 . Fig. 7 shows the UV–Vis spectra of the protonated PANI solution in chloroform to PANI-CSA and PANI-DBSA. Three distinct transitions at 370, 410 and 850 nm can be seen w20x. Such a spectrum is characteristic of isolated polarons in coil-like conformation of PANI chains. 3.6. The effect of protonating agents and sulfonation for electrical conductiÕity
Fig. 7. Changes in UV–Vis spectra of doped PANI solution in chloroform.
nated PANIrSPC composite is larger than that of CSA protonated PANIrSPC composite, due to the solvation effect as the conformation of expanded coil by large molecule w22–24x. In this composite, the percolation threshold is in the vicinity of 15 wt.%. This can be explained by the fact that the structure consists of a three-dimensional network of conducting polymer aggregates in the PC or SPC matrix. Electrical conductivity
Fig. 8Ža. and Žb. represents the changes of electrical conductivity with the kinds of protonating agents and the sulfonation effect of the PC. The composites, in this study, were blended using protonated PANI and SPC. Charge carriers normally induce coulombic interactions between a positive charge and a negative one w21x. Also, the dispersion of PANI grains in the SPC matrix was considerably enhanced by the presence of the coulombic interaction. As a result, this sulfonation effect causes an increase of electrical conductivity. In this figure, the smaller the content of PANI, the larger the difference of electrical conductivity. Further, the electrical conductivity of DBSA proto-
Fig. 6. FT-IR spectra of protonated PANI solution in chloroform: Ža. PANI; Žb. PANI-CSA; Žc. PANI-DBSA.
Fig. 8. Ža. Electrical conductivity of the PANIrSPC composites as a function of protonation. Žb. Electrical conductivity of the conducting polymer composites as a function of sulfonation.
W.-J. Lee et al.r Synthetic Metals 113 (2000) 237–243
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increased to 7.5 Srcm with the amount of PANI complex protonated with DBSA having a long alkyl chain. 3.7. Temperature dependence of electrical conductiÕity in PANI composite Fig. 9 shows the variations of conductivity in the composite films with temperatures in the range from room temperature to 1608C. An increase of resistance was observed with increasing temperature. These phenomena can be explained by the fact that resistance is increased to expand into the space between PANI particles due to the thermal vibration of PC matrix w25x. Fig. 10 shows the temperature dependence of the electrical conductivity in the range from y1968C to room temperature, and an increase in electrical conductivity was observed with increasing temperature. This can be explained by the variable range hopping expression w26x, which is a charge transfer model of the semiconductor region. This equation can be explained as follows: s ŽT . A exp wyŽTorT .g x, where To is a characteristic temperature and g is the temperature index. The experimental result is linearized when g is 1r2. This result might be due to the coulombic interaction w27x.
Fig. 10. Electrical conductivity changes of composites between y1968C and 208C: Ža. PANI-DBSArSPC Žb. PANI-CSArSPC. ŽB: PANI Ž5 wt.%.; ^: PANIŽ10 wt.%.; ': PANI Ž15 wt.%.; `: PANI Ž20 wt.%.; v: PANI Ž25 wt.%...
3.8. Mechanical properties of composite film Fig. 11 represents the stress–strain curve of PC or SPCrDBSA protonated PANI composite films with the contents of PANI. The values of the tensile strengths of the
Fig. 9. Electrical conductivity changes of composites between 208C and 1608C: Ža. PANI-DBSArSPC; Žb. PANI-CSArSPC. ŽB: PANI Ž5 wt.%.; ^: PANI Ž10 wt.%.; ': PANI Ž15 wt.%.; `: PANIŽ20 wt.%., v: PANI Ž25 wt.%...
Fig. 11. Ultimate tensile strength of PANI-DBSArPC and PANIDBSArSPC composite films.
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two cases are almost the same. The mechanical property depends mainly on the content of PANI. When the content of the PANI are low, the mechanical property is satisfactorily high yet it decreases steeply in the vicinity of percolation threshold. This might be explained by the fact that below percolation, the PC or SPC matrix is a continuous phase and the PANI is dispersed as a disperse phase, and above the percolation threshold, the three-dimensional network of small conducting granular aggregates in the PC or SPC matrix is well formed. 3.9. Characteristics of morphology Fig. 12 represents the views of scanning electron microscopy ŽSEM. for the surfaces of PANIrPC composites
and PANIrSPC composites. In Fig. 12Ža. – Žc., the PANI complex in PANIrPC composite is seen to distribute as small spherical granules within the matrix. In this case, the phase separation still remains even as the interfacial tension is acted between the DBSA protonated PANI and the PC matrix. This phase separation results in a decline of both the mechanical properties and the electrical conductivity. Fig. 12Žd. – Žf. represents the surfaces of PANIrSPC composites. In spite of the lower content of PANI, the PANI complex within the SPC matrix is well distributed due to the effect of sulfonation. In other words, this phenomena might lead to an increase of the electrical conductivity and mechanical strength by inducing an electrostatic interaction between the PANI complex and the SPC matrix.
Fig. 12. SEM images of conducting polymer composites; Ža. – Žc.: PANIrPC composite; Žd. – Žf.: PANIrSPC composite.
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4. Conclusions The ion exchange capacity reached the critical point Ž2.0 meqrg. when chlorosulfuric acid as a sulfonating agent used 2.5 mol. The electrical conductivity of the SPCrPANI composite was larger than that of the PCrPANI composite. This phenomena might be due to an induced electrostatic interaction between the PANI complex and the SPC matrix. The temperature dependence of conductivity in composites in the range from y1968C to 1608C was explained by a variable range hopping model and thermal vibration of the matrix. The sulfonation effect not only lowers the percolation threshold in the composite, but also increases the electrical conductivity and mechanical properties. In SPCrPANI conducting composites, electrical conductivity increased up to 7.5 Srcm with the amount of PANI complex protonated with DBSA having a long alkyl chain. Acknowledgements This research was supported by the Korea Science and Engineering Foundation ŽKOSEF. under contract with KOSEF 981-1109-045-2. References w1x J.M. Pope, N. Oyama, J. Electrochem. Soc. 145 Ž6. Ž1998. 1893. w2x H. Tsutsumi, M. Araki, K. Onimura, T. Oishi, Synth. Met. 97 Ž1998. 53.
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w3x J.G. Killian, B.M. Coffery, F. Gao, T.O. Poehler, P.C. Searson, J. Electrochem. Soc. 143 Ž3. Ž1996. 936. w4x O. Niwa, T. Tamamura, J. Chem. Soc., Chem. Commun. Ž1984. 817. w5x S. Yang, E. Ruckenstein, Polym. Commun. 31 Ž1990. 275. w6x E. Benseddik, M. Makhlonki, J.C. Bernede, S. Lefant, A. Pron, Synth. Met. 72 Ž1995. 237. w7x R.L. Greene, G.B. Street, L.J. Suter, Phys. Rev. Lett. 34 Ž1975. 557. w8x Y. Cao, A. Andreatta, A.J. Heeger, P. Smith, Polymer 30 Ž1989. 2305. w9x Y. Cao, P. Smith, A.J. Heeger, Synth. Met. 48 Ž1992. 91. w10x Y. Cao, P. Smith, A.J. Heeger, Synth. Met. 57 Ž1993. 3514. w11x J.Y. Lee, D.Y. Kim, C.Y. Kim, Synth. Met. 74 Ž1995. 103. w12x O. Niwa, J. Chem. Soc., Chem. Commun. Ž1984. 817. w13x S. Yang, E. Ruckenstein, Polym. Commun. 31 Ž1990. 275. w14x E. Benseddik, M. Makhlonki, J.C. Bernede, S. Lefant, A. Pron, Synth. Met. 72 Ž1995. 237. w15x D.R. Paul, J.W. Barlow, J. Macromol. Sci. C-1 Ž1980. 109. w16x J.A. Brydson, Polymeric Materials, Butterworths, London, 1989. w17x J.-M. Liu, L. Sun, S.C., Yang, US Patent 5.489.400 Ž1996.. w18x J.-M. Liu, L. Sun, J.-H. Hwang, S.C. Yang, Mater. Res. Soc. Symp. Proc. 247 Ž1992. 601. w19x S. Fisher, R. Kunin, Anal. Chem. 7 Ž1955. 27. w20x S. Huang, A.G. MacDiarmid, Polymer 34 Ž9. Ž1993. 1833. w21x A. Skotheim ŽEd.., Handbook of Conducting Polymer Vol. 1 Marcel Dekker, New York, 1986, p. 83. w22x A.G. MacDiarmid, A.J. Epstein, Synth. Met. 65 Ž1994. 103. w23x A.G. MacDiarmid, A.J. Epstein, Synth. Met. 69 Ž1995. 85. w24x J.K. Avlyanov, Y. Min, A.G. MacDiarmid, A.J. Epstein, Synth. Met. 72 Ž1995. 65. w25x W.D. Callister Jr., Materials Science and Engineering, 4th Edn., Wiley, Chichester, New York, 1994. w26x Z.H. Wang, C. Li, E.M. Scherr, A.G. MacDiarmid, A.J. Epstein, Phys. Rev. Lett. 66 Ž1991. 745. w27x M. Reghu, Y. Cao, A.J. Heeger, Synth. Met. 65 Ž1994. 167.
Electrical properties of polyanilinersulfonated polycarbonate blends Wan-Jin Lee ) , Yong-Ju Kim, Shinyoung Kaang Faculty of Applied Chemistry, College of Engineering, Chonnam National UniÕersity, 300 Yongbong-dong, Puk-gu, Kwangju 500-757, South Korea Received 4 August 1999; received in revised form 1 December 1999; accepted 7 February 2000
Abstract A conducting composite using polyaniline ŽPANI. as the conducting polymer and polycarbonate ŽPC. as a matrix was prepared by a blending method. Chloroform was used as a solvent in the blending. The PANI was protonated using camphor sulfonic acid ŽCSA. or a dodecylbenzene sulfonic acid ŽDBSA. such as alkylbenzenesulfonic acid. A sulfonic group was introduced into the structure of the PC in order to enhance the coulombic interaction between each phase of the composite. The effect of ionic groups in sulfonated PC ŽSPC. was monitored using measurements of both the mechanical and thermal properties. Using the presence of protonating agents and the amount of PANI complex, both the electrical conductivity and morphology were measured. Electrical conductivity increased to 7.5 Srcm with the amount of PANI complex protonated with DBSA having a long alkyl chain. q 2000 Elsevier Science S.A. All rights reserved. Keywords: Polyaniline; Sulfonation; Polycarbonate; Blends
1. Introduction The development of polymers with high electrical conductivity has attracted significant research interest in the last decade due to the possibility of new applications w1–3x. There has also been progress in the processability of polythiophene and polypyrrole, as well as of polyaniline ŽPANI. w4–6x. One of the conducting polymers that has attracted considerable interest in the last few years is PANI. PANI seems to be one of the best candidates for the preparation of polymer-based conducting polymer composites. It is stable in a normal atmosphere, and recently, significant progress has been achieved in the preparation of processable forms of PANI w7,8x. Cao et al. w9,10x and Lee et al. w11x showed that PANI, protonated with camphor sulfonic acid ŽCSA. or dodecylbenzene sulfonic acid ŽDBSA., can be processed from solutions. A soluble PANI complex can be obtained through doping by CSA or DBSA because the molecular interfacial interaction is decreased. This means that the PANI complex doped by CSA or DBSA is ther-
) Corresponding author. Tel.: q82-62-530-1895; fax: q82-62-5301889. E-mail address: [email protected] ŽW.-J. Lee..
mally stable compared with the PANI complex doped by small molecules such as HCl. Recently, several conductive composites of protonated PANI with insulating polymer have been reported elsewhere w12–14x. However, the two phases are basically immiscible, and the phase separation is still to be found between each phase. If the miscibility of these blends were to be enhanced between phases, the electrical and mechanical properties would be increased. The morphology in immiscible blends is determined by various parameters, such as interfacial tension, volume fractions, and viscosity ratios w15x. Various methods to enhance properties in immiscible blends include using precursors, compatibilizers such as block copolymers, or introducing ionic polymers w16x. By introducing ionic groups such as a sulfonic group to the insulating polymer, such as polystyrene and polycarbonate ŽPC., it is possible to enhance the miscibility between two phases w17,18x. Therefore, this will minimize the phase separation between the conducting polymer and the insulating polymer. This would lead to an increase in the mechanical and electrical properties, due to an increase of the compatibility and the induction of electrostatic interaction. In this article, we report on the preparation of conductive, flexible composites of PANI and sulfonated PC ŽSPC.,
0379-6779r00r$ - see front matter q 2000 Elsevier Science S.A. All rights reserved. PII: S 0 3 7 9 - 6 7 7 9 Ž 0 0 . 0 0 2 1 6 - 2
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and the effect of the introduction of ionic groups on the compatibility of the electrical and mechanical properties.
where Y represents the amount of consumed HCl, NNaOH is the normal concentration of NaOH, and NHCl is the normal concentration of HCl.
2. Experimental
2.6. Measurements of electrically conductiÕe polymer composites
2.1. Materials The PC was obtained from Sumitomo Žtype 201-15 resin, MW 22000, density 1.20, Tg 1508C., and was distilled under vacuum before use. The PANI emeraldine base was commercially purchased from Aldrich and was distilled under vacuum before use and stored in nitrogen. The CSA and DBSA used protonating agents that were purchased from Aldrich. The chloroform ŽJunsei Chemical., used as a solvent, and chlorosulfuric acid ŽKanto Chemical., used as a sulfonating agent, were used without purification. 2.2. Protonation of polyemeraldine base Two groups of protonating agents were used: CSA and DBSA. For the protonation reaction, a polyemeraldine base was mixed with the appropriate protonating agent in the molar ratio of wacid moleculesx:wPANI merx s 0.5. This mixture was then dissolved and vigorously stirred at 408C for 24 h, the time required to reach the maximum dissolution, and then centrifuged to remove minor solids. 2.3. Sulfonation of PC PC was dissolved to form a 10 wt.% solution in chloroform by mechanical mixing at room temperature. Then, chlorosulfuric acid in an additional four-neck flask under nitrogen gas was dropped slowly with vigorous stirring. The reaction was continued for 5 h. Sulfonated products were filtered, and washed with Na 2 CO 3 and methanol. Finally, the powder sample was obtained after dried SPC in a vacuum oven.
The conductivity of the sample in the plane direction was determined by a standard four-probe method. Infrared studies and UV–Vis absorption spectra of composite films were carried out on a Mattson 1000 FT-IR spectrometer and Hitachi U-3501 UV–Vis absorption spectrometer, respectively. NMR studies for structural analysis of SPC were carried out using a Varian Unity Plus-300 and 300 MHz proton nuclear magnetic resonance spectroscopy. Thermal gravimetric analysis ŽTGA. measurements were performed on a TA TGA7 instrument. The sample was cut to the size required by the ASTM D638. Tensile testing was performed using an Instron testing instrument ŽUniframe TC-55, Satec System. at room temperature with a load cell of 200 lb and cross-head speed of 3.0 mmrmin. Scanning electron micrographs of the electrical composite film were obtained with a Jeol JSM-5400 instrument.
3. Results and discussion 3.1. FT-IR analysis of SPC The results of the FT-IR and NMR of the original sample PC were compared with that of the SPC. As shown in Fig. 1, the typical peaks of SO 3 H are absorption at 1250–1150 and 1060–1030 cmy1 . The strong band of the frequency, 1250–1150 cmy1 , can be ascribed to stretch vibration for S5O, and the absorption band at the 1060– 1030 cmy1 is assigned to the symmetric stretching band. However, the stretching band of C5O is 1765–1720 cmy1 in the ester group for PC, while the C`O`C for asymmetric stretching band is 1290–1180 cmy1 , and the O`C`O peak is 645–575 cmy1 . The spectra were so complex that
2.4. Preparation of composite film The protonated PANI complex was mixed in an appropriate ratio with PC or SPC in chloroform. This mixture was cast on a glass substrate as film types of about 50-mm thickness, and then the solvent was evaporated in the vacuum oven at 708C. 2.5. The capacity of ion exchange of SPC The ion exchange capacity was measured by the Fisher’s back titration method w19x at room temperature according to the concentrations of chlorosulfuric acid. The ion exchange capacity was calculated by the following equation: the capacity of ion exchange Ž meqrg. s Ž 50 = NNaOH y Y = NHCl . rweight of polymer,
Fig. 1. FT-IR spectra of PC and SPC.
W.-J. Lee et al.r Synthetic Metals 113 (2000) 237–243
Fig. 2. NMR spectra of PC and SPC.
they could not easily be used, due to an overlap of the absorption of the sulfonic group and ester group of PC. So, the NMR analysis is shown in the following figure. 3.2. NMR analysis of SPC In Fig. 2, the 1 H NMR spectra of SPC and PC were compared. In the case of the PC, the symmetric peaks of the benzene rings appeared at 7.0–7.4 ppm. In the vicinity of 2 ppm, one peak of C`C`C structure is evident. In the case of SPC, a new peak of benzene ring at 6.7–7.2 ppm is made to appear by the disappearance of the symmetric structure in order to introduce the SO 3 H group to PC. Also, one peak of the C`C`C structure, about 2 ppm, is broken because the balance of the benzene ring in both sides was lost. Fig. 3 shows the chemical structure of synthesized SPC. The reactive substitution position is situated meta to the aryl ester linkage in the bisphenol unit. This position is the most favorable site because it is electrophilically activated by CH 3 , rather than by ester. 3.3. Ion exchange capacity of SPC Fig. 4 shows the change of the ion exchange capacity according to the concentration of chlorosulfuric acid when the PC was sulfonated. This sulfonation was carried out at
Fig. 3. Reaction scheme of SPC preparation.
239
Fig. 4. Relationship between sulfonation degrees and sulfonating agent contents.
258C for 5 h. The ion exchange capacity was measured by the Fisher’s back titration method. The ion exchange capacity increased with an increasing CSA concentration, but it did not increase more than 2 mol. It then reached its critical point at over 2.5 mol. In this study, the experiment was carried out at the condition of 2.5 mol. 3.4. Thermal property of SPC Fig. 5 shows the TGA of PC and SPC. In the case of SPC, the weight loss appeared in the vicinity of 1808C. This result can be explained by the fact that the sulfonic group introduced PC matrix decomposed due to the unstable structure of the SOy 3 group. The benzene ring of the PC matrix broke down in the vicinity of 2678C, possibly causing the weight loss. 3.5. Protonation of the PANI by CSA and DBSA Generally, a conducting polymer is not easily dissolved by common organic solvents, due to its large intermolecular interfacial tension. But, a soluble PANI complex can be obtained to dope by CSA or DBSA because the molecular
Fig. 5. TGA thermograms of PC and SPC.
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interfacial interaction is decreased. This means that the PANI complex, doped by CSA or DBSA, is more thermally stable compared to the PANI complex doped by small molecule like HCl. Fig. 6 shows the results of the FT-IR analysis to confirm the protonation of PANI doped by CSA or DBSA such as alkylbenzenesulfonic acid. Fig. 6Žb. shows the peaks of the PANI complex protonated by CSA in chloroform. The stretching band of S5O represents an absorption band of 1200 cmy1 , and C5O band of cyclohexanone is evident at 1600 cmy1 , because of the effect of ring strain. Fig. 6Žc. represents the peaks of PANI protonated by DBSA in chloroform. The C`H band of the aromatic ring becomes evident at 3000 cmy1 , and then the aliphatic peaks, such as –CH 3 and CH 2 by alkyl chain, can be observed at 2990–2850 cmy1 . Also, the stretching band of S5O represents an absorption band of 1200 cmy1 . Fig. 7 shows the UV–Vis spectra of the protonated PANI solution in chloroform to PANI-CSA and PANI-DBSA. Three distinct transitions at 370, 410 and 850 nm can be seen w20x. Such a spectrum is characteristic of isolated polarons in coil-like conformation of PANI chains. 3.6. The effect of protonating agents and sulfonation for electrical conductiÕity
Fig. 7. Changes in UV–Vis spectra of doped PANI solution in chloroform.
nated PANIrSPC composite is larger than that of CSA protonated PANIrSPC composite, due to the solvation effect as the conformation of expanded coil by large molecule w22–24x. In this composite, the percolation threshold is in the vicinity of 15 wt.%. This can be explained by the fact that the structure consists of a three-dimensional network of conducting polymer aggregates in the PC or SPC matrix. Electrical conductivity
Fig. 8Ža. and Žb. represents the changes of electrical conductivity with the kinds of protonating agents and the sulfonation effect of the PC. The composites, in this study, were blended using protonated PANI and SPC. Charge carriers normally induce coulombic interactions between a positive charge and a negative one w21x. Also, the dispersion of PANI grains in the SPC matrix was considerably enhanced by the presence of the coulombic interaction. As a result, this sulfonation effect causes an increase of electrical conductivity. In this figure, the smaller the content of PANI, the larger the difference of electrical conductivity. Further, the electrical conductivity of DBSA proto-
Fig. 6. FT-IR spectra of protonated PANI solution in chloroform: Ža. PANI; Žb. PANI-CSA; Žc. PANI-DBSA.
Fig. 8. Ža. Electrical conductivity of the PANIrSPC composites as a function of protonation. Žb. Electrical conductivity of the conducting polymer composites as a function of sulfonation.
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increased to 7.5 Srcm with the amount of PANI complex protonated with DBSA having a long alkyl chain. 3.7. Temperature dependence of electrical conductiÕity in PANI composite Fig. 9 shows the variations of conductivity in the composite films with temperatures in the range from room temperature to 1608C. An increase of resistance was observed with increasing temperature. These phenomena can be explained by the fact that resistance is increased to expand into the space between PANI particles due to the thermal vibration of PC matrix w25x. Fig. 10 shows the temperature dependence of the electrical conductivity in the range from y1968C to room temperature, and an increase in electrical conductivity was observed with increasing temperature. This can be explained by the variable range hopping expression w26x, which is a charge transfer model of the semiconductor region. This equation can be explained as follows: s ŽT . A exp wyŽTorT .g x, where To is a characteristic temperature and g is the temperature index. The experimental result is linearized when g is 1r2. This result might be due to the coulombic interaction w27x.
Fig. 10. Electrical conductivity changes of composites between y1968C and 208C: Ža. PANI-DBSArSPC Žb. PANI-CSArSPC. ŽB: PANI Ž5 wt.%.; ^: PANIŽ10 wt.%.; ': PANI Ž15 wt.%.; `: PANI Ž20 wt.%.; v: PANI Ž25 wt.%...
3.8. Mechanical properties of composite film Fig. 11 represents the stress–strain curve of PC or SPCrDBSA protonated PANI composite films with the contents of PANI. The values of the tensile strengths of the
Fig. 9. Electrical conductivity changes of composites between 208C and 1608C: Ža. PANI-DBSArSPC; Žb. PANI-CSArSPC. ŽB: PANI Ž5 wt.%.; ^: PANI Ž10 wt.%.; ': PANI Ž15 wt.%.; `: PANIŽ20 wt.%., v: PANI Ž25 wt.%...
Fig. 11. Ultimate tensile strength of PANI-DBSArPC and PANIDBSArSPC composite films.
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two cases are almost the same. The mechanical property depends mainly on the content of PANI. When the content of the PANI are low, the mechanical property is satisfactorily high yet it decreases steeply in the vicinity of percolation threshold. This might be explained by the fact that below percolation, the PC or SPC matrix is a continuous phase and the PANI is dispersed as a disperse phase, and above the percolation threshold, the three-dimensional network of small conducting granular aggregates in the PC or SPC matrix is well formed. 3.9. Characteristics of morphology Fig. 12 represents the views of scanning electron microscopy ŽSEM. for the surfaces of PANIrPC composites
and PANIrSPC composites. In Fig. 12Ža. – Žc., the PANI complex in PANIrPC composite is seen to distribute as small spherical granules within the matrix. In this case, the phase separation still remains even as the interfacial tension is acted between the DBSA protonated PANI and the PC matrix. This phase separation results in a decline of both the mechanical properties and the electrical conductivity. Fig. 12Žd. – Žf. represents the surfaces of PANIrSPC composites. In spite of the lower content of PANI, the PANI complex within the SPC matrix is well distributed due to the effect of sulfonation. In other words, this phenomena might lead to an increase of the electrical conductivity and mechanical strength by inducing an electrostatic interaction between the PANI complex and the SPC matrix.
Fig. 12. SEM images of conducting polymer composites; Ža. – Žc.: PANIrPC composite; Žd. – Žf.: PANIrSPC composite.
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4. Conclusions The ion exchange capacity reached the critical point Ž2.0 meqrg. when chlorosulfuric acid as a sulfonating agent used 2.5 mol. The electrical conductivity of the SPCrPANI composite was larger than that of the PCrPANI composite. This phenomena might be due to an induced electrostatic interaction between the PANI complex and the SPC matrix. The temperature dependence of conductivity in composites in the range from y1968C to 1608C was explained by a variable range hopping model and thermal vibration of the matrix. The sulfonation effect not only lowers the percolation threshold in the composite, but also increases the electrical conductivity and mechanical properties. In SPCrPANI conducting composites, electrical conductivity increased up to 7.5 Srcm with the amount of PANI complex protonated with DBSA having a long alkyl chain. Acknowledgements This research was supported by the Korea Science and Engineering Foundation ŽKOSEF. under contract with KOSEF 981-1109-045-2. References w1x J.M. Pope, N. Oyama, J. Electrochem. Soc. 145 Ž6. Ž1998. 1893. w2x H. Tsutsumi, M. Araki, K. Onimura, T. Oishi, Synth. Met. 97 Ž1998. 53.
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