- Email: [email protected]
Surfactant effects on the polyaniline film
Synthetic Metals 88 (1997) 209–212
Surfactant effects on the polyaniline film Lin-Tao Cai a,U, Shi-Bing Yao b, Shao-Min Zhou b b
a Department of Chemistry, Nanjing University, Nanjing 210093, China The State Key Laboratory for Physical Chemistry of Solid Surfaces, Department of Chemistry, Xiamen University, Xiamen 361005, China
Received 24 January 1997; accepted 21 February 1997
Abstract Polyaniline (PANI) film prepared in the presence of surfactant anions, such as sodium dodecylbenzenesulfonate (SDBS) and sodium dodecylsulfate (SDS), was characterized. The conductivity of PANI/SDBS film was 65.9 S cmy1, which is five times higher than that of the parent PANI film without the influence of surfactants. The UV–Vis spectra and X-ray diffraction pattern of the PANI/SDBS film showed increase of polaron delocalization, structural order of polymer chains and higher crystallinity, resulting from the decreased degree of degradation due to the hydrophobic effect of the surfactant molecules on the film growth, and the large surfactant anions immobilized in the polymer backbone and the stabilized polymer chain. Keywords: Polyaniline and derivatives; Surfactant anions; Conductivity
1. Introduction Polyaniline (PANI) has been widely investigated due to its specific doping and conductivity characterization and its applications in electronic devices [1,2]. PANI film is known to be easily degradable [3] due to the over-oxidation hydrolysis in the acidic electrolyte, which reduces the quality and stability of the film. The surfactant molecules can provide a hydrophobic micro-effect with a controlled electrochemical catalysis [4], effects of orientation and solubilization due to the micelle media formed, and greatly improved quality of the polymer films. It was found that polypyrrole grown in the presence of large amphiphilic surfactant anions has improved electrical conductivity and activity [5–9]. Recently, Heeger and co-workers [10] reported that the conductivity of PANI can be increased up to 400 S cmy1 in solution-cast films using camphorsulfonic acid (CAS) and up to 250 S cmy1 with dodecyl benzenesulfonic acid (DBSA) as dopant to produce PANI with higher quality and reduced disorder. Our previous work [11] has shown that the anionic micelles of sodium dodecylsulfate (SDS) can catalyse the electropolymerization process of aniline and reduce its oxidation-limited potential, which leads to an enhanced electroactivity and a more uniform polymer film. In this work, we further investigate the electrochemical properties, structure and conductivity of the PANI film deposU
Corresponding author. [email protected]
Fax:
q86
25
331
7761;
e-mail:
ited from aqueous solutions containing sodium dodecylbenzenesulfonate (SDBS) or SDS as a dopant. The study has been focused on the effect of the surfactant anions on the film quality and order.
2. Experimental
All electrochemical studies were performed with a conventional three-electrode system, using a platinum working electrode (diameter 6 mm), a platinum counter electrode and a saturated calomel electrode (SCE) as a reference. The electrochemical procedure and equipment have been described in detail elsewhere [12]. The PANI films were prepared in a solution of 0.5 M aniline and 0.5 M H2SO4 by potential cycling between y0.2 and q0.75 V (versus SCE) at a 50 mV sy1 sweep rate with addition of 10y4 M SDS or SDBS. In situ conductivity was measured using four-microprobe techniques [12]. In situ UV–Vis spectra were recorded using an optical multichannel analyser (EG&G PARC OMAIII, model 1460) equipped with a gated diode array detector. Xray diffraction studies were performed using a Rigaku Rotaflex D/max-C XRD system using a copper target Cu Ka ˚ ). (ls1.5406 A
0379-6779/97/$17.00 q 1997 Elsevier Science S.A. All rights reserved PII S 0 3 7 9 - 6 7 7 9 ( 9 7 ) 0 3 8 5 2 - 6
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higher pH. The presence of DBSy anions within the film would prevent the expulsion of protons or cations, which results in the first oxidation peak being shifted positively. As in the higher oxidation state, the anions of the electrolyte may be inserted into the polymer matrix in company with the doping of protons in its bipolaron state, which may maintain the film’s conductivity at the high potential, as will be mentioned below. 3.2. In situ conductivity measurements
AH(myn)q ™AqmHqqney m
The in situ conductivity measurements on the polymer film were performed in 0.5 M H2SO4 solution. The relationship between potential and conductivity is shown in Fig. 2. In comparison with the parent PANI film formed in the absence of surfactants, the curves for the polymer film under the influence of surfactants are greatly promoted and shifted to more positive potentials. The maximum conductivity of PANI/SDBS film (s Bs65.9 S cmy1) is increased about five-fold over that of the parent PANI film (s 0s11.6 S cmy1), but, for the PANI/SDS film (s Ss24.1 S cmy1), the conductivity is only doubled. Thus, SDBS is obviously a better dopant for higher conducting PANI. The potential (Eas0.5 V) of the maximum conductivity for PANI film doped with surfactants is shifted positively by 100 mV, compared with the parent PANI film. It is suggested that the electropolymerization process for PANI is based on a radical cation intermediate coupling [15]. The surfactant molecules provide a hydrophobic effect preventing the polymer degradation, and thus improving the degree of structural order of the polymer film, and the large amphiphilic surfactant anions are immobilized on the polymer backbone with positive charge, neutralized and stabilized for the polymer chains; the polarons transfer may be faster, which leads to increases of conductivity.
EsE0y0.059(m/n)pH (Ts25 8C)
3.3. UV–Vis spectra and X-ray diffraction
Hence, the first redox reaction involves a loss of one proton per electron at pH 0 to 1 and has no change of protons at pH)1. The second redox peak involves a loss of two protons per electron. These results are analogous with the reported results by MacDiarmid and co-workers [13] and Lacroix and Diaz [14]. The proposed redox process is shown in the following scheme:
UV–Vis spectral changes (normalized by the leucoemeraldine spectrum at y0.2 V) recorded in 0.5 M H2SO4 solution during oxidation of PANI/SDBS film and PANI film are illustrated in Fig. 3. The spectra of PANI/SDBS show a bathochromic shift (red shift) compared with those of PANI. The
Fig. 1. Relationship between the oxidation peak potential (50 mV sy1) and pH for PANI/SDBS film (full lines) and PANI film (dotted lines). E1 and E2 are the first and second oxidation peaks, respectively.
3. Results and discussion 3.1. Redox properties of PANI/SDBS film The voltammogram of PANI/SDBS clearly consists of two well-resolved peaks corresponding to the two redox processes depending on the pH values in the electrolytic solutions. The relationship between the oxidation peak potential and pH adjusted with different HCl concentrations in 6 M NaCl solutions is shown in Fig. 1. The value of the first oxidation peak is fitted into two segments of straight lines: the slope of the line from pH 0 to 1 is y59.5 mV/pH for the PANI film and y56 mV/pH for the PANI/SDBS film, while that from pH 1 to 2.1 is 0 mV/pH. The first peak potential of PANI/ SDBS shifts positively against that of PANI. The second oxidation peak shifts at the rate of y117 mV/pH in the pH range 0 to 2.1. According to the Nernst equation for the pHdependent redox process:
oxid 1
PANI/DBSy/Hq ( or Mq) l PANIq/DBSy oxid 2
l PANIqq/DBSy/xAy/yHq In its intermediate oxidation state, the positively charged PANIq chain has a strong mutual attraction with the surfactant anions (DBSy), which not only stabilizes the polysemiquinone radical cations (polarons) with the delocalization of electrons along the chain, but also impedes the incorporation of other anions (Ay). The charge neutrality of the film is apparently maintained by the doping–redoping of the protons (Hq) at the lower pH or the cations (Mq) at the
Fig. 2. Potential dependence of the conductivities in 0.5 M H2SO4 solution for the PANI film (e) and the PANI film prepared in the presence of SDBS (j) and SDS (n).
Journal: SYNMET (Synthetic Metals)
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(Fig. 4(b)), several stronger diffraction peaks are clearly observed due to the scattering of interchain packing, indicating that the polymer subchains become more rigid and ordered and the orientation of interchain packing is achieved in the presence of surfactant anions. The higher crystallinity and the more-ordered arrangement of the chain may enhance the conductivity of PANI/SDBS. These results are in excellent agreement with those of in situ conductivity measurement and optical spectra above.
Fig. 3. UV–Vis spectral changes (normalized by the leucoemeraldine spectrum at y0.2 V) recorded in 0.5 M H2SO4 solution during oxidation of PANI/SDBS film (full lines) and PANI film (dotted lines). Potential is 0.3 V (a,b) and 0.8 V (c,d).
4. Conclusions The results reported in this study show that the polymerization of polyaniline in the presence of large surfactant anions, such as SDBS and SDS, leads to the deposition of films having specific properties and characteristics. The PANI/ SDBS film shows a good electroactivity and stability, a greatly enhanced conductivity and a more-ordered arrangement of the chain. This may allow modulation of the electrical and optical properties of the polymer films for use in novel applications.
Acknowledgements This project was supported by the National Natural Science Foundation of China. Fig. 4. X-ray diffraction spectra of the PANI film (a) and the PANI/SDBS film (b).
References electronic transition of the radical cation or polaron band [16,17] at 436 nm in PANI shifts to 457 nm in PANI/SDBS. As the levels of oxidation of polymer film increase, the polaron bands disappear gradually and a strong broader absorption due to exciton transition of the quinoid rings [18] grows at the same time, shifted by 50 nm from 499 to 549 nm. These results indicate that the surfactant anions cause a decrease in the bandgap and a more-ordered chain structure, the polarons in the PANI/SDBS film are more delocalized than in the PANI film, and the conductivity would be increased. Moreover, in the highest oxidation state of PANI, the curve (Fig. 3(d)) contains a more secondary structure peak due to the degradation, as the film is unstable at the high potential. However, the PANI/SDBS (Fig. 3(c)) shows a better stability. Another factor that could affect the conductivity is the chain packing of the polymer. A comparison of the X-ray diffraction of the various PANI films is shown in Fig. 4. For the parent PANI film [19,20] prepared in the absence of surfactants, as can be seen in Fig. 4(a), a broad weak peak near 2us24.78 shows that the film exhibits an amorphous structure. This lower crystallographic order of the polymer chains causes increased separation of the chains and lower conductivity. On the contrary, under the influence of SDBS
[1] A.G. MacDiarmid and A.J. Epstein, Faraday Discuss. Chem. Soc., 88 (1989) 317. [2] M. Kaneko and H. Nakamura, J. Chem. Soc., Chem. Commun., (1985) 1441. [3] T. Kobayashi, H. Yoneyama and H. Tamura, J. Electroanal. Chem., 161 (1984) 419. [4] J.F. Rusling, Acc. Chem. Res., 24 (1991) 75. [5] J.M. Pernaut, R.C.D. Peres, V.F. Juliano and M.A. DePaoli, J. Electroanal. Chem., 274 (1989) 225. [6] R.C.D. Peres, J.M. Pernaut and M.A. DePaoli, Synth. Met., 28 (1989) C59. [7] W. Wernet, M. Monkenbusch and G. Wegner, Makromol. Chem. Rapid Commun., 5 (1984) 157. [8] M.A. DePaoli, S. Panero, P. Prosperi and B. Scrosati, Electrochim. Acta, 35 (1990) 1145. [9] L.F. Warren and D.F. Anderson, J. Electrochem. Soc., 134 (1987) 101. [10] Y. Cao, P. Smith and A.J. Heeger, Synth. Met., 48 (1992) 91. [11] L.T. Cai, S.B. Yao and S.M. Zhou, Chem. J. Chin. Univ., 17 (1996) 269. [12] L.T. Cai, S.B. Yao and S.M. Zhou, J. Electroanal. Chem., in press. [13] W.S. Huang, B.D. Humphrey and A.G. MacDiarmid, J. Chem. Soc., Faraday Trans. 1, 82 (1986) 2385. [14] J.C. Lacroix and A.F. Diaz, J. Electrochem. Soc., 135 (1988) 1457. [15] Y.B. Shim, M.S. Won and S.M. Park, J. Electrochem. Soc., 137 (1990) 538. [16] Y. Cao, P. Smith and A.J. Heeger, Synth. Met., 32 (1988) 263. [17] S. Stafstro¨m, J.L. Bre´das, A.J. Epstein, H.S. Woo, D.B. Tanner, W.S. Huang and A.G. MacDiarmid, Phys. Rev. Lett., 59 (1987) 1464.
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[18] A.J. Epstein, J.M. Ginder, F. Zuo, R.W. Bigelow, H.S. Woo, D.B. Tanner, A.F. Richter, W.S. Huang and A.G. MacDiarmid, Synth. Met., 18 (1987) 303. [19] E.M. Scherr, A.G. MacDiarmid, S.K. Manohar, J.G. Masters, Y. Sun, X. Tang, M.A. Druy, P.J. Glatkowski, V. Cajibe, J.E. Fischer,
K.R. Cromack, M.E. Jozefowicz, J.M. Ginder, R.P. McCall and A.J. Epstein, Synth. Met., 41–43 (1991) 735. [20] M.E. Jozefowicz, A.J. Epstein, J.P. Pouget, J.G. Masters, A. Ray, Y. Sun, X. Tang and A.G. MacDiarmid, Synth. Met., 41–43 (1991) 723.
Journal: SYNMET (Synthetic Metals)
Article: 4986
Surfactant effects on the polyaniline film Lin-Tao Cai a,U, Shi-Bing Yao b, Shao-Min Zhou b b
a Department of Chemistry, Nanjing University, Nanjing 210093, China The State Key Laboratory for Physical Chemistry of Solid Surfaces, Department of Chemistry, Xiamen University, Xiamen 361005, China
Received 24 January 1997; accepted 21 February 1997
Abstract Polyaniline (PANI) film prepared in the presence of surfactant anions, such as sodium dodecylbenzenesulfonate (SDBS) and sodium dodecylsulfate (SDS), was characterized. The conductivity of PANI/SDBS film was 65.9 S cmy1, which is five times higher than that of the parent PANI film without the influence of surfactants. The UV–Vis spectra and X-ray diffraction pattern of the PANI/SDBS film showed increase of polaron delocalization, structural order of polymer chains and higher crystallinity, resulting from the decreased degree of degradation due to the hydrophobic effect of the surfactant molecules on the film growth, and the large surfactant anions immobilized in the polymer backbone and the stabilized polymer chain. Keywords: Polyaniline and derivatives; Surfactant anions; Conductivity
1. Introduction Polyaniline (PANI) has been widely investigated due to its specific doping and conductivity characterization and its applications in electronic devices [1,2]. PANI film is known to be easily degradable [3] due to the over-oxidation hydrolysis in the acidic electrolyte, which reduces the quality and stability of the film. The surfactant molecules can provide a hydrophobic micro-effect with a controlled electrochemical catalysis [4], effects of orientation and solubilization due to the micelle media formed, and greatly improved quality of the polymer films. It was found that polypyrrole grown in the presence of large amphiphilic surfactant anions has improved electrical conductivity and activity [5–9]. Recently, Heeger and co-workers [10] reported that the conductivity of PANI can be increased up to 400 S cmy1 in solution-cast films using camphorsulfonic acid (CAS) and up to 250 S cmy1 with dodecyl benzenesulfonic acid (DBSA) as dopant to produce PANI with higher quality and reduced disorder. Our previous work [11] has shown that the anionic micelles of sodium dodecylsulfate (SDS) can catalyse the electropolymerization process of aniline and reduce its oxidation-limited potential, which leads to an enhanced electroactivity and a more uniform polymer film. In this work, we further investigate the electrochemical properties, structure and conductivity of the PANI film deposU
Corresponding author. [email protected]
Fax:
q86
25
331
7761;
e-mail:
ited from aqueous solutions containing sodium dodecylbenzenesulfonate (SDBS) or SDS as a dopant. The study has been focused on the effect of the surfactant anions on the film quality and order.
2. Experimental
All electrochemical studies were performed with a conventional three-electrode system, using a platinum working electrode (diameter 6 mm), a platinum counter electrode and a saturated calomel electrode (SCE) as a reference. The electrochemical procedure and equipment have been described in detail elsewhere [12]. The PANI films were prepared in a solution of 0.5 M aniline and 0.5 M H2SO4 by potential cycling between y0.2 and q0.75 V (versus SCE) at a 50 mV sy1 sweep rate with addition of 10y4 M SDS or SDBS. In situ conductivity was measured using four-microprobe techniques [12]. In situ UV–Vis spectra were recorded using an optical multichannel analyser (EG&G PARC OMAIII, model 1460) equipped with a gated diode array detector. Xray diffraction studies were performed using a Rigaku Rotaflex D/max-C XRD system using a copper target Cu Ka ˚ ). (ls1.5406 A
0379-6779/97/$17.00 q 1997 Elsevier Science S.A. All rights reserved PII S 0 3 7 9 - 6 7 7 9 ( 9 7 ) 0 3 8 5 2 - 6
Journal: SYNMET (Synthetic Metals)
Article: 4986
210
L.-T. Cai et al. / Synthetic Metals 88 (1997) 209–212
higher pH. The presence of DBSy anions within the film would prevent the expulsion of protons or cations, which results in the first oxidation peak being shifted positively. As in the higher oxidation state, the anions of the electrolyte may be inserted into the polymer matrix in company with the doping of protons in its bipolaron state, which may maintain the film’s conductivity at the high potential, as will be mentioned below. 3.2. In situ conductivity measurements
AH(myn)q ™AqmHqqney m
The in situ conductivity measurements on the polymer film were performed in 0.5 M H2SO4 solution. The relationship between potential and conductivity is shown in Fig. 2. In comparison with the parent PANI film formed in the absence of surfactants, the curves for the polymer film under the influence of surfactants are greatly promoted and shifted to more positive potentials. The maximum conductivity of PANI/SDBS film (s Bs65.9 S cmy1) is increased about five-fold over that of the parent PANI film (s 0s11.6 S cmy1), but, for the PANI/SDS film (s Ss24.1 S cmy1), the conductivity is only doubled. Thus, SDBS is obviously a better dopant for higher conducting PANI. The potential (Eas0.5 V) of the maximum conductivity for PANI film doped with surfactants is shifted positively by 100 mV, compared with the parent PANI film. It is suggested that the electropolymerization process for PANI is based on a radical cation intermediate coupling [15]. The surfactant molecules provide a hydrophobic effect preventing the polymer degradation, and thus improving the degree of structural order of the polymer film, and the large amphiphilic surfactant anions are immobilized on the polymer backbone with positive charge, neutralized and stabilized for the polymer chains; the polarons transfer may be faster, which leads to increases of conductivity.
EsE0y0.059(m/n)pH (Ts25 8C)
3.3. UV–Vis spectra and X-ray diffraction
Hence, the first redox reaction involves a loss of one proton per electron at pH 0 to 1 and has no change of protons at pH)1. The second redox peak involves a loss of two protons per electron. These results are analogous with the reported results by MacDiarmid and co-workers [13] and Lacroix and Diaz [14]. The proposed redox process is shown in the following scheme:
UV–Vis spectral changes (normalized by the leucoemeraldine spectrum at y0.2 V) recorded in 0.5 M H2SO4 solution during oxidation of PANI/SDBS film and PANI film are illustrated in Fig. 3. The spectra of PANI/SDBS show a bathochromic shift (red shift) compared with those of PANI. The
Fig. 1. Relationship between the oxidation peak potential (50 mV sy1) and pH for PANI/SDBS film (full lines) and PANI film (dotted lines). E1 and E2 are the first and second oxidation peaks, respectively.
3. Results and discussion 3.1. Redox properties of PANI/SDBS film The voltammogram of PANI/SDBS clearly consists of two well-resolved peaks corresponding to the two redox processes depending on the pH values in the electrolytic solutions. The relationship between the oxidation peak potential and pH adjusted with different HCl concentrations in 6 M NaCl solutions is shown in Fig. 1. The value of the first oxidation peak is fitted into two segments of straight lines: the slope of the line from pH 0 to 1 is y59.5 mV/pH for the PANI film and y56 mV/pH for the PANI/SDBS film, while that from pH 1 to 2.1 is 0 mV/pH. The first peak potential of PANI/ SDBS shifts positively against that of PANI. The second oxidation peak shifts at the rate of y117 mV/pH in the pH range 0 to 2.1. According to the Nernst equation for the pHdependent redox process:
oxid 1
PANI/DBSy/Hq ( or Mq) l PANIq/DBSy oxid 2
l PANIqq/DBSy/xAy/yHq In its intermediate oxidation state, the positively charged PANIq chain has a strong mutual attraction with the surfactant anions (DBSy), which not only stabilizes the polysemiquinone radical cations (polarons) with the delocalization of electrons along the chain, but also impedes the incorporation of other anions (Ay). The charge neutrality of the film is apparently maintained by the doping–redoping of the protons (Hq) at the lower pH or the cations (Mq) at the
Fig. 2. Potential dependence of the conductivities in 0.5 M H2SO4 solution for the PANI film (e) and the PANI film prepared in the presence of SDBS (j) and SDS (n).
Journal: SYNMET (Synthetic Metals)
Article: 4986
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211
(Fig. 4(b)), several stronger diffraction peaks are clearly observed due to the scattering of interchain packing, indicating that the polymer subchains become more rigid and ordered and the orientation of interchain packing is achieved in the presence of surfactant anions. The higher crystallinity and the more-ordered arrangement of the chain may enhance the conductivity of PANI/SDBS. These results are in excellent agreement with those of in situ conductivity measurement and optical spectra above.
Fig. 3. UV–Vis spectral changes (normalized by the leucoemeraldine spectrum at y0.2 V) recorded in 0.5 M H2SO4 solution during oxidation of PANI/SDBS film (full lines) and PANI film (dotted lines). Potential is 0.3 V (a,b) and 0.8 V (c,d).
4. Conclusions The results reported in this study show that the polymerization of polyaniline in the presence of large surfactant anions, such as SDBS and SDS, leads to the deposition of films having specific properties and characteristics. The PANI/ SDBS film shows a good electroactivity and stability, a greatly enhanced conductivity and a more-ordered arrangement of the chain. This may allow modulation of the electrical and optical properties of the polymer films for use in novel applications.
Acknowledgements This project was supported by the National Natural Science Foundation of China. Fig. 4. X-ray diffraction spectra of the PANI film (a) and the PANI/SDBS film (b).
References electronic transition of the radical cation or polaron band [16,17] at 436 nm in PANI shifts to 457 nm in PANI/SDBS. As the levels of oxidation of polymer film increase, the polaron bands disappear gradually and a strong broader absorption due to exciton transition of the quinoid rings [18] grows at the same time, shifted by 50 nm from 499 to 549 nm. These results indicate that the surfactant anions cause a decrease in the bandgap and a more-ordered chain structure, the polarons in the PANI/SDBS film are more delocalized than in the PANI film, and the conductivity would be increased. Moreover, in the highest oxidation state of PANI, the curve (Fig. 3(d)) contains a more secondary structure peak due to the degradation, as the film is unstable at the high potential. However, the PANI/SDBS (Fig. 3(c)) shows a better stability. Another factor that could affect the conductivity is the chain packing of the polymer. A comparison of the X-ray diffraction of the various PANI films is shown in Fig. 4. For the parent PANI film [19,20] prepared in the absence of surfactants, as can be seen in Fig. 4(a), a broad weak peak near 2us24.78 shows that the film exhibits an amorphous structure. This lower crystallographic order of the polymer chains causes increased separation of the chains and lower conductivity. On the contrary, under the influence of SDBS
[1] A.G. MacDiarmid and A.J. Epstein, Faraday Discuss. Chem. Soc., 88 (1989) 317. [2] M. Kaneko and H. Nakamura, J. Chem. Soc., Chem. Commun., (1985) 1441. [3] T. Kobayashi, H. Yoneyama and H. Tamura, J. Electroanal. Chem., 161 (1984) 419. [4] J.F. Rusling, Acc. Chem. Res., 24 (1991) 75. [5] J.M. Pernaut, R.C.D. Peres, V.F. Juliano and M.A. DePaoli, J. Electroanal. Chem., 274 (1989) 225. [6] R.C.D. Peres, J.M. Pernaut and M.A. DePaoli, Synth. Met., 28 (1989) C59. [7] W. Wernet, M. Monkenbusch and G. Wegner, Makromol. Chem. Rapid Commun., 5 (1984) 157. [8] M.A. DePaoli, S. Panero, P. Prosperi and B. Scrosati, Electrochim. Acta, 35 (1990) 1145. [9] L.F. Warren and D.F. Anderson, J. Electrochem. Soc., 134 (1987) 101. [10] Y. Cao, P. Smith and A.J. Heeger, Synth. Met., 48 (1992) 91. [11] L.T. Cai, S.B. Yao and S.M. Zhou, Chem. J. Chin. Univ., 17 (1996) 269. [12] L.T. Cai, S.B. Yao and S.M. Zhou, J. Electroanal. Chem., in press. [13] W.S. Huang, B.D. Humphrey and A.G. MacDiarmid, J. Chem. Soc., Faraday Trans. 1, 82 (1986) 2385. [14] J.C. Lacroix and A.F. Diaz, J. Electrochem. Soc., 135 (1988) 1457. [15] Y.B. Shim, M.S. Won and S.M. Park, J. Electrochem. Soc., 137 (1990) 538. [16] Y. Cao, P. Smith and A.J. Heeger, Synth. Met., 32 (1988) 263. [17] S. Stafstro¨m, J.L. Bre´das, A.J. Epstein, H.S. Woo, D.B. Tanner, W.S. Huang and A.G. MacDiarmid, Phys. Rev. Lett., 59 (1987) 1464.
Journal: SYNMET (Synthetic Metals)
Article: 4986
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[18] A.J. Epstein, J.M. Ginder, F. Zuo, R.W. Bigelow, H.S. Woo, D.B. Tanner, A.F. Richter, W.S. Huang and A.G. MacDiarmid, Synth. Met., 18 (1987) 303. [19] E.M. Scherr, A.G. MacDiarmid, S.K. Manohar, J.G. Masters, Y. Sun, X. Tang, M.A. Druy, P.J. Glatkowski, V. Cajibe, J.E. Fischer,
K.R. Cromack, M.E. Jozefowicz, J.M. Ginder, R.P. McCall and A.J. Epstein, Synth. Met., 41–43 (1991) 735. [20] M.E. Jozefowicz, A.J. Epstein, J.P. Pouget, J.G. Masters, A. Ray, Y. Sun, X. Tang and A.G. MacDiarmid, Synth. Met., 41–43 (1991) 723.
Journal: SYNMET (Synthetic Metals)
Article: 4986