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Effect of the polymer electrolyte on the electrochemical polymerization of aniline
EIecrrochimfcuAcro, Vol. 36, No. 1, pp.87-91, 1991 Printed in Great Britain.
0013468691$3.00+ 0.00 0 1990.Pergalnon Press pk.
EFFECT OF THE POLYMER ELECTROLYTE ON THE ELECTROCHEMICAL POLYMERIZATION OF ANILINE KENJI HYODO,* MAKI OMAE and YOSHIHARU KAGAMI
Tsukuba Research Laboratories, Mitsubishi Paper Mills Ltd, 46 Wadai Tsukuba-city, Ibaraki 300-42, Japan (Received 3 January 1990; in revisedform 13 March 1990) A&r&-Aniline was electrochemically polymerized in aqueous electrolyte containing polymer electrolytes which have the sulfonate group. The very small amount of polymer electrolytes were selectively incorporated into the polyaniline matrix. The added polymer electrolytes accelerate the film growth rate. The surface morphology of the films was also changed dramatically with the addition of the polymer electrolytes.
(PAMPS) (Aldrich Chemical Co.) and poly(vinylsulfonic acid sodium salt) (PVS) (Polysciences Inc. M.W. 2000) were used without further purification. All electrochemical experiments were carried out in aqueous solution at room temperature using a potentiogalbanostat HA5OlG and function generator HB105 (Hokuto Denko Ltd). The potentials noted below were measured by the saturated calomel electrode (SCE). The data were stored in a personal computer and cyclic-voltammograms were plotted with a Hewlett Packard 7470A plotter. Polyaniline was deposited onto the platinum foil (1 x 1 x 0.1 cm) by sweeping the potential of the electrode in 50 ml of 1.0 mol dm-’ HC104 aqueous solution containing 0.088 mol dme3 aniline. Potential was cycled between -200 and 750 mV at the scanning rate of 50 mV s-‘. As long as a potential less than 750 mV was used, the degradation of the polyaniline was suppressed. Aqueous polymer electrolytes were added to the above electrolyte and p-toluenesulfonic acid was used as the low molecular weight anion.
INTRODUCTION Over one hundred years have passed since Letheby started investigating polyaniline[ 11.Particularly since the report by Diaz et u1.[2], many works have been done on the electrochemical study of polyanilinemainly because of the potential applications of polyaniline in batteries and electrochromic displays. Quite recently a polyaniline battery was launched onto the market[3]. To functionalize or to improve the physical properties of electrochemically polymerized conducting polymers, polymer electrolytes are used as dopant[4,5]. Whilst there are many reports on polypyrrole-containing polymer electrolytes, there are few reports on the reaction of polyaniline with polymer electrolytes[6]. Yoneyama et al. have reported synthesis of polyaniline containing Nafion(7j; Bidan er al. have reported the synthesis of polyaniline containing heteropolyanions[S] and recently they have reported on the one-step electrosynthesis of a polyanilin+Nafion composite filmp]. From the viewpoint of basic electrochemistry and applications, the interaction of polymer electrolytes and polyaniline is very interesting. We have already reported on the high ion selective electrochemical synthesis of the polyaniline[lO] and ion selective irreversible electrochemical doping of the polyaniline by polymer electrolyte. In this paper we state the effect of the polymer electrolyte[ll] during the electrochemical polymerization of the aniline.
ESCA measurement
ESCA measurement was conducted using the ESCA MC5400 (Perkin Elmer Co.) system. The vacuum level during the measurement was lower than 10e9 Torr. 38 eV of pass energy and 0.1 eV of step voltage was used for the multiplex measurement. 44.74 eV of pass energy and 0.5 eV of step voltage was used to obtain the survey spectra. The X-ray power of the Al-K, radiation was about 400 W. Any correction of the effect of the charge-up was not conducted since in this paper we do not discuss about the absolute chemical shift of the elements. The correction for the ionization cross section was conducted to get the atomic concentration.
EXPERIMENTAL Sample preparation
All the chemicals used in this study were reagent grade and were used without further purification unless stated otherwise. Aniline was purified by simple distillation. Poly(styrenesulfonic acid sodium salt) (PSS) (Polysciences Inc. M.W. 500,000), poly(2-acrylamido-2-methyl-l-propane sulfonic acid)
SEA4 observation
The scanning electron micrographs were measured using a Hitachi S-2300 scanning electron microscope. The micrographs of the conducting films were 87
K. HYOW et al.
1
400
600 BINDING
ENERGY
(eV
1
Fig. 1. ESCA survey spectrum of polyaniline polymerized in 1 N HCIO, and small amount of PVS. measured with a 10 nm platinum-palladium alloy film sputtered on the film surface. Acceleration voltage was 25 kV.
RESULTS AND DISCUSSION Ion selectivity
Figure 1 shows the ESCA survey spectrum of the polyaniline which was polymerized in 50 ml of 1 N HC104 aqueous solution containing 0.088 mol dm-’ aniline and 2 ml of 0.1 N poly(vinylsulfonic acid sodium salt) (PVS) aqueous solution. The core level of the carbon Is, nitrogen Is, and oxygen 1s appeared around 286, 402, 534eV, respectively. To find the peaks due to the dopants more clearly, the scan in the region between 250 eV and 0 eV was repeated four times. The two peaks at 168 and 233 eV are derived from sulfur 2p of the sulfonic group of the PVS but the peak derived from Cl of the perchlorate anion is hardly observed. This provides clear evidence that the polymer electrolyte is highly selectively incorporated into the polyaniline matrix as we have already reported[ lo]. As was mentioned previously, this kind of selectivity seems to be due to the polymer effect, ie the local concentration of the sulfonic group near the surface of the electrode becomes higher than the perchlorate anion in the electrolyte once a part of the polymer electrolyte is incorporated into the polyaniline matrix. The atomic concentrations of the films obtained are summarized in Table 1. It is obvious that polymer electrolytes such as poly(2-acrylamido-2-methyl-lpropane sulfonic acid) @‘AMPS), poly(styrenesul-
fonic acid sodium salt) (PSS) and PVS are selectively incorporated into the polyaniline matrix whereas p-toluene sulfonic acid (monomer model of the polymer electrolyte) is hardly incorporated because of the low concentration compared to the perchlorate anion. The molar ratios of sulfur to nitrogen were calculated from Table 1. The values were 0.14, 0.24 and 0.23, for the polyanilines containing PAMPS, PSS and PVS. It suggests that one sulfonate group is incorporated for almost every four aniline units. Effect on the polymerization rate
During the sample preparation, we found that film growth rate was remarkably affected by a small amount of the added polymer electrolyte. Film growth rate was easily evaluated during the electrochemical polymerization by the anodic peak which appeared around 200mV. To compare the film growth rate, the polyanilines were deposited in the different electrolytes by scanning the potential between -200 and 750 mV ten times at the scanning rate of 50 mV s-i. Figure 2 shows the cyclic voltammograms of the polyanilines in 1 N aqueous HC104 solution. Figure 2a shows the cyclic voltammogram of the polyaniline deposited in the 1 N aqueous HC104 and aniline. The anodic peaks appearing around 200 and 700 mV are very small which suggests that the film growth rate is very low. The peaks become much larger when small amounts of polymer electrolytes were added. The amount of the added polymer electrolytes is indeed very small compared to the 1 N aqueous HC104. (2 ml of 0.1 N aqueous solution of the polymer electrolyte was added to the 50 ml of 1 N aqueous HC104 .)
Table 1. Summary of the atomic concentration of the polyanilines (wt%) Element
Polymer*
01s
Nls
Cls
c12p
s2p
PAn/HCIO, PAn/HClO,/PTS (a) PAn/HClO,/PAMPS (b) PAn/HClO,/PSS (c) PAn/HClO,/PVS (d)
16.9 15.9 17.5 17.2 17.1
9.2 8.6 8.4 5.8 7.4
71.9 73.9 70.4 73.5 70.7
1.1 0.9 0.5 0.0 0.1
0.9 0.7 3.2 3.6 4.6
*Polyanilines (PAn) were polymerized in 50 ml of 1 N HClO, and 2 ml of 0.1 N polymer electrolyte such as (b) PAMPS, (c) PSS and (d) PVS (p-toluenesulfonic acid (PTS) was used as the monomer model of the electrolyte).
89
Electrochemical polymerization of aniline I ( mA/cm2) n (d)
V(vsS.C.E.)
Fig. 2. Cyclic voltammogcams of polyanilines measured in 1 N aqueous HClO, solution at a scan rate of 5OmVs-‘; polymerized in HClO, (a), with PAMPS (a), with PSS (c) and with PVS (d).
The degree of the effect depended upon the polymer electrolytes used. The order of the effect to the film growth rate is PVS > PSS > PAMPS. By considering the difference of the molecular weights of PVS (M.W.2000) and PSS (M.W. 500,000), the molecular weights itself does not seem to affect the growth rate signifkantiy when the chemical structure of the polymer electrolyte is different. To investigate the mechanism of this effect, the onset potentials of the first anodic scan were compared but no trend was observed to explain the above
407
404 BINDING
order. To find out the difference of the effect, ESCA spectra of the nitrogen of each polyanilines were measured (Fig. 3). Samples were prepared in exactly the same way as in the case of Fig. 2. After deposition the sample-swere held at the potential of 400 mV for about 5 mm and then washed in water and acetonitrile. Figure 3 also shows the deconvoluted results with the dotted, lines. The detailed explanations of the deconvoluted spectrum were discussed and the second peak which has the higher binding energy is assigned to the positively charged nitrogen atoms in
404 ElNDING
395 401 ENERGY (eV1
401 398 ENERGY (eV)
(d 1
407
404 BINDING
401 398 ENERGY (eV1
395
BINDING
ENERGY
(eV1
Fig. 3. ESCA nitrogen multiplex spectra of polyanilines polymerized in HCIO, (a), with PAMPS (b), with PSS (c) and with PVS (d).
90
K. HYODO et al.
the chain[l2]. If the interaction of the sulfonate groups of the polymer electrolytes were the same as the perchlorate anion, the ratio of the positively charged nitrogen atoms and neutral nitrogen atoms in the polyaniline chain should be almost equal regardless of the species of the dopants. Figure 3 shows the clear difference of the amount of the positively charged nitrogen atoms. The order of the amount of the positively charged nitrogen is the same as the order of the film growth rate. PVS which grows the film fastest has the largest portion of the positively charged nitrogen of all (Figs 3ad). PAMPS affects the film growth rate least of all in the
Fig. 4. Scanning
Electron sulfonic
polymer electrolytes and has the lowest ratio of the positively charged nitrogen compared to PVS and PSS. It seems likely that the dopant which has the higher interaction with the nitrogen atom of the polyaniline is more effective to grow the film. The interaction of the sulfonate group with the nitrogen atoms of the polyaniline may be due to the difference of the pK, of the polymer electrolyte, but further evidence for that has yet to be obtained. Morphology change caused by the polymer electroIyte
To investigate the effect of the polymer electrolytes on the electrochemical polymerization of the aniline,
Micrographs (SEMs) of polyanilines polymerized in HCIO, a(l), withp-toluene acid a(2), with PAMPS (b), with PSS (c) and with PVS (d).
Electrochemical polymerization of aniline the surface morphology of the polyanilines obtained was observed by the scanning electron micrograph (SEM). The SEMs for the electrochemically polymerized anilines in different electrolytes were shown in Fig. 4. Figures 4a(l) and a(2) are almost identical, which means that the small amount of added p-toluene sulfonic acid affects the morphology of the film very little. It is quite reasonable to think that the added p-toluene sulfonic acid is hardly incorporated into the polyaniline matrices because of the significant difference of the concentration in the electrolyte compared to the perchlorate anion. This “noodlelike” morphology was reported by Diaz[l3] and MacDiarmid[ 141. Figures 4b-d show the SEM of the polyanilines deposited in the electrolyte which contained small amounts of PAMPS(b), PSS(c) and PVS(d). The morphology of the films has changed dramatically compared to a(1) and a(2); ie the noodle like morphology changed to grain. Small amounts of the added polymer electrolyte affect the morphology of the films. This kind of difference comes from the selectively incorporated polymer electrolyte. The same phenomenon was observed in the case of polypyrrole and poly-N-methylpyrrole[5].
CONCLUSION The effect of the polymer electrolyte on the electrochemical polymerization of aniline was investigated. The very small amount of the polymer electrolytes which were added to the electrolyte were highly selectively incorporated into the polyaniline matrix, and the selectivity differs depending on the species of the polymer electrolyte used. The addition of the polymer electrolytes also affects the film growth rate of the polyaniline and such effect may come from the
91
difference of the interactions of the dopant anions with nitrogen atoms of the polyaniline. The film morphology is also affected by the added polymer electrolytes. Acknowledgements-The
authors would like to thank Mr Shigehiro Maeda for the SEM photographs and also
would like to thank Dr Kaxunaka Endo for the valuable experimental support and fruitful discussion.
REFERENCES 1. H. Letheby, J. them. Sot. 161 (1862). 2. A. F. Diaz and J. A. Logan, J. electroanal. Chem. 111, 111 (1980). 3. T. Nakajima and T. Kawagoe, Synrh. Metals 28, c629 (1989). 4. W. Wemet and G. Wegner, Makromol. Chem. 188,1465 (1987). 5. K. Hyodo and M. Omae, Electrochim. Acta 35, 827 (1990). 6. K. Hyodo, M. Nozaki and A. G. MacDiarmid, Rep&. Prog. Polymer Phys. Jpn 29, 423 (1986). 7. T. Hirai, S. Kuwabata and H. Yoneyarna, J. electrothem. Sot. 135, 1132 (1988). 8. G. Bidan et al., Mater. Sci. Forum 42, 51 (1989). 9. G. Bidan and B. Ehui, J. them. Sot. them. Commun., 1568 (1989). 10. K. Hyodo and M. Nozaki, Electrochim. Acta 33, 165 (1988). 11. K. Hyodo and M. Omae, Electrochim. Acta MS 311. 12. R. Kessel. G. Hansen and J. W. Schultxe. Ber. Bunsenges.‘phys. Chem. 92, 710 (1988). 13. J.-C. LaCroix and A. F. Diaz, Makromol. Chem., Macromol. Sym. 8, 17 (1987); J. electrochem. Sot. 135, 1457 (1988). 14. W.-S.‘ Wuang, B. D. Humphrey and A. G. MacDiarmid, J. them. Sot., Faraday Trans. 182, 2385 (1986).
0013468691$3.00+ 0.00 0 1990.Pergalnon Press pk.
EFFECT OF THE POLYMER ELECTROLYTE ON THE ELECTROCHEMICAL POLYMERIZATION OF ANILINE KENJI HYODO,* MAKI OMAE and YOSHIHARU KAGAMI
Tsukuba Research Laboratories, Mitsubishi Paper Mills Ltd, 46 Wadai Tsukuba-city, Ibaraki 300-42, Japan (Received 3 January 1990; in revisedform 13 March 1990) A&r&-Aniline was electrochemically polymerized in aqueous electrolyte containing polymer electrolytes which have the sulfonate group. The very small amount of polymer electrolytes were selectively incorporated into the polyaniline matrix. The added polymer electrolytes accelerate the film growth rate. The surface morphology of the films was also changed dramatically with the addition of the polymer electrolytes.
(PAMPS) (Aldrich Chemical Co.) and poly(vinylsulfonic acid sodium salt) (PVS) (Polysciences Inc. M.W. 2000) were used without further purification. All electrochemical experiments were carried out in aqueous solution at room temperature using a potentiogalbanostat HA5OlG and function generator HB105 (Hokuto Denko Ltd). The potentials noted below were measured by the saturated calomel electrode (SCE). The data were stored in a personal computer and cyclic-voltammograms were plotted with a Hewlett Packard 7470A plotter. Polyaniline was deposited onto the platinum foil (1 x 1 x 0.1 cm) by sweeping the potential of the electrode in 50 ml of 1.0 mol dm-’ HC104 aqueous solution containing 0.088 mol dme3 aniline. Potential was cycled between -200 and 750 mV at the scanning rate of 50 mV s-‘. As long as a potential less than 750 mV was used, the degradation of the polyaniline was suppressed. Aqueous polymer electrolytes were added to the above electrolyte and p-toluenesulfonic acid was used as the low molecular weight anion.
INTRODUCTION Over one hundred years have passed since Letheby started investigating polyaniline[ 11.Particularly since the report by Diaz et u1.[2], many works have been done on the electrochemical study of polyanilinemainly because of the potential applications of polyaniline in batteries and electrochromic displays. Quite recently a polyaniline battery was launched onto the market[3]. To functionalize or to improve the physical properties of electrochemically polymerized conducting polymers, polymer electrolytes are used as dopant[4,5]. Whilst there are many reports on polypyrrole-containing polymer electrolytes, there are few reports on the reaction of polyaniline with polymer electrolytes[6]. Yoneyama et al. have reported synthesis of polyaniline containing Nafion(7j; Bidan er al. have reported the synthesis of polyaniline containing heteropolyanions[S] and recently they have reported on the one-step electrosynthesis of a polyanilin+Nafion composite filmp]. From the viewpoint of basic electrochemistry and applications, the interaction of polymer electrolytes and polyaniline is very interesting. We have already reported on the high ion selective electrochemical synthesis of the polyaniline[lO] and ion selective irreversible electrochemical doping of the polyaniline by polymer electrolyte. In this paper we state the effect of the polymer electrolyte[ll] during the electrochemical polymerization of the aniline.
ESCA measurement
ESCA measurement was conducted using the ESCA MC5400 (Perkin Elmer Co.) system. The vacuum level during the measurement was lower than 10e9 Torr. 38 eV of pass energy and 0.1 eV of step voltage was used for the multiplex measurement. 44.74 eV of pass energy and 0.5 eV of step voltage was used to obtain the survey spectra. The X-ray power of the Al-K, radiation was about 400 W. Any correction of the effect of the charge-up was not conducted since in this paper we do not discuss about the absolute chemical shift of the elements. The correction for the ionization cross section was conducted to get the atomic concentration.
EXPERIMENTAL Sample preparation
All the chemicals used in this study were reagent grade and were used without further purification unless stated otherwise. Aniline was purified by simple distillation. Poly(styrenesulfonic acid sodium salt) (PSS) (Polysciences Inc. M.W. 500,000), poly(2-acrylamido-2-methyl-l-propane sulfonic acid)
SEA4 observation
The scanning electron micrographs were measured using a Hitachi S-2300 scanning electron microscope. The micrographs of the conducting films were 87
K. HYOW et al.
1
400
600 BINDING
ENERGY
(eV
1
Fig. 1. ESCA survey spectrum of polyaniline polymerized in 1 N HCIO, and small amount of PVS. measured with a 10 nm platinum-palladium alloy film sputtered on the film surface. Acceleration voltage was 25 kV.
RESULTS AND DISCUSSION Ion selectivity
Figure 1 shows the ESCA survey spectrum of the polyaniline which was polymerized in 50 ml of 1 N HC104 aqueous solution containing 0.088 mol dm-’ aniline and 2 ml of 0.1 N poly(vinylsulfonic acid sodium salt) (PVS) aqueous solution. The core level of the carbon Is, nitrogen Is, and oxygen 1s appeared around 286, 402, 534eV, respectively. To find the peaks due to the dopants more clearly, the scan in the region between 250 eV and 0 eV was repeated four times. The two peaks at 168 and 233 eV are derived from sulfur 2p of the sulfonic group of the PVS but the peak derived from Cl of the perchlorate anion is hardly observed. This provides clear evidence that the polymer electrolyte is highly selectively incorporated into the polyaniline matrix as we have already reported[ lo]. As was mentioned previously, this kind of selectivity seems to be due to the polymer effect, ie the local concentration of the sulfonic group near the surface of the electrode becomes higher than the perchlorate anion in the electrolyte once a part of the polymer electrolyte is incorporated into the polyaniline matrix. The atomic concentrations of the films obtained are summarized in Table 1. It is obvious that polymer electrolytes such as poly(2-acrylamido-2-methyl-lpropane sulfonic acid) @‘AMPS), poly(styrenesul-
fonic acid sodium salt) (PSS) and PVS are selectively incorporated into the polyaniline matrix whereas p-toluene sulfonic acid (monomer model of the polymer electrolyte) is hardly incorporated because of the low concentration compared to the perchlorate anion. The molar ratios of sulfur to nitrogen were calculated from Table 1. The values were 0.14, 0.24 and 0.23, for the polyanilines containing PAMPS, PSS and PVS. It suggests that one sulfonate group is incorporated for almost every four aniline units. Effect on the polymerization rate
During the sample preparation, we found that film growth rate was remarkably affected by a small amount of the added polymer electrolyte. Film growth rate was easily evaluated during the electrochemical polymerization by the anodic peak which appeared around 200mV. To compare the film growth rate, the polyanilines were deposited in the different electrolytes by scanning the potential between -200 and 750 mV ten times at the scanning rate of 50 mV s-i. Figure 2 shows the cyclic voltammograms of the polyanilines in 1 N aqueous HC104 solution. Figure 2a shows the cyclic voltammogram of the polyaniline deposited in the 1 N aqueous HC104 and aniline. The anodic peaks appearing around 200 and 700 mV are very small which suggests that the film growth rate is very low. The peaks become much larger when small amounts of polymer electrolytes were added. The amount of the added polymer electrolytes is indeed very small compared to the 1 N aqueous HC104. (2 ml of 0.1 N aqueous solution of the polymer electrolyte was added to the 50 ml of 1 N aqueous HC104 .)
Table 1. Summary of the atomic concentration of the polyanilines (wt%) Element
Polymer*
01s
Nls
Cls
c12p
s2p
PAn/HCIO, PAn/HClO,/PTS (a) PAn/HClO,/PAMPS (b) PAn/HClO,/PSS (c) PAn/HClO,/PVS (d)
16.9 15.9 17.5 17.2 17.1
9.2 8.6 8.4 5.8 7.4
71.9 73.9 70.4 73.5 70.7
1.1 0.9 0.5 0.0 0.1
0.9 0.7 3.2 3.6 4.6
*Polyanilines (PAn) were polymerized in 50 ml of 1 N HClO, and 2 ml of 0.1 N polymer electrolyte such as (b) PAMPS, (c) PSS and (d) PVS (p-toluenesulfonic acid (PTS) was used as the monomer model of the electrolyte).
89
Electrochemical polymerization of aniline I ( mA/cm2) n (d)
V(vsS.C.E.)
Fig. 2. Cyclic voltammogcams of polyanilines measured in 1 N aqueous HClO, solution at a scan rate of 5OmVs-‘; polymerized in HClO, (a), with PAMPS (a), with PSS (c) and with PVS (d).
The degree of the effect depended upon the polymer electrolytes used. The order of the effect to the film growth rate is PVS > PSS > PAMPS. By considering the difference of the molecular weights of PVS (M.W.2000) and PSS (M.W. 500,000), the molecular weights itself does not seem to affect the growth rate signifkantiy when the chemical structure of the polymer electrolyte is different. To investigate the mechanism of this effect, the onset potentials of the first anodic scan were compared but no trend was observed to explain the above
407
404 BINDING
order. To find out the difference of the effect, ESCA spectra of the nitrogen of each polyanilines were measured (Fig. 3). Samples were prepared in exactly the same way as in the case of Fig. 2. After deposition the sample-swere held at the potential of 400 mV for about 5 mm and then washed in water and acetonitrile. Figure 3 also shows the deconvoluted results with the dotted, lines. The detailed explanations of the deconvoluted spectrum were discussed and the second peak which has the higher binding energy is assigned to the positively charged nitrogen atoms in
404 ElNDING
395 401 ENERGY (eV1
401 398 ENERGY (eV)
(d 1
407
404 BINDING
401 398 ENERGY (eV1
395
BINDING
ENERGY
(eV1
Fig. 3. ESCA nitrogen multiplex spectra of polyanilines polymerized in HCIO, (a), with PAMPS (b), with PSS (c) and with PVS (d).
90
K. HYODO et al.
the chain[l2]. If the interaction of the sulfonate groups of the polymer electrolytes were the same as the perchlorate anion, the ratio of the positively charged nitrogen atoms and neutral nitrogen atoms in the polyaniline chain should be almost equal regardless of the species of the dopants. Figure 3 shows the clear difference of the amount of the positively charged nitrogen atoms. The order of the amount of the positively charged nitrogen is the same as the order of the film growth rate. PVS which grows the film fastest has the largest portion of the positively charged nitrogen of all (Figs 3ad). PAMPS affects the film growth rate least of all in the
Fig. 4. Scanning
Electron sulfonic
polymer electrolytes and has the lowest ratio of the positively charged nitrogen compared to PVS and PSS. It seems likely that the dopant which has the higher interaction with the nitrogen atom of the polyaniline is more effective to grow the film. The interaction of the sulfonate group with the nitrogen atoms of the polyaniline may be due to the difference of the pK, of the polymer electrolyte, but further evidence for that has yet to be obtained. Morphology change caused by the polymer electroIyte
To investigate the effect of the polymer electrolytes on the electrochemical polymerization of the aniline,
Micrographs (SEMs) of polyanilines polymerized in HCIO, a(l), withp-toluene acid a(2), with PAMPS (b), with PSS (c) and with PVS (d).
Electrochemical polymerization of aniline the surface morphology of the polyanilines obtained was observed by the scanning electron micrograph (SEM). The SEMs for the electrochemically polymerized anilines in different electrolytes were shown in Fig. 4. Figures 4a(l) and a(2) are almost identical, which means that the small amount of added p-toluene sulfonic acid affects the morphology of the film very little. It is quite reasonable to think that the added p-toluene sulfonic acid is hardly incorporated into the polyaniline matrices because of the significant difference of the concentration in the electrolyte compared to the perchlorate anion. This “noodlelike” morphology was reported by Diaz[l3] and MacDiarmid[ 141. Figures 4b-d show the SEM of the polyanilines deposited in the electrolyte which contained small amounts of PAMPS(b), PSS(c) and PVS(d). The morphology of the films has changed dramatically compared to a(1) and a(2); ie the noodle like morphology changed to grain. Small amounts of the added polymer electrolyte affect the morphology of the films. This kind of difference comes from the selectively incorporated polymer electrolyte. The same phenomenon was observed in the case of polypyrrole and poly-N-methylpyrrole[5].
CONCLUSION The effect of the polymer electrolyte on the electrochemical polymerization of aniline was investigated. The very small amount of the polymer electrolytes which were added to the electrolyte were highly selectively incorporated into the polyaniline matrix, and the selectivity differs depending on the species of the polymer electrolyte used. The addition of the polymer electrolytes also affects the film growth rate of the polyaniline and such effect may come from the
91
difference of the interactions of the dopant anions with nitrogen atoms of the polyaniline. The film morphology is also affected by the added polymer electrolytes. Acknowledgements-The
authors would like to thank Mr Shigehiro Maeda for the SEM photographs and also
would like to thank Dr Kaxunaka Endo for the valuable experimental support and fruitful discussion.
REFERENCES 1. H. Letheby, J. them. Sot. 161 (1862). 2. A. F. Diaz and J. A. Logan, J. electroanal. Chem. 111, 111 (1980). 3. T. Nakajima and T. Kawagoe, Synrh. Metals 28, c629 (1989). 4. W. Wemet and G. Wegner, Makromol. Chem. 188,1465 (1987). 5. K. Hyodo and M. Omae, Electrochim. Acta 35, 827 (1990). 6. K. Hyodo, M. Nozaki and A. G. MacDiarmid, Rep&. Prog. Polymer Phys. Jpn 29, 423 (1986). 7. T. Hirai, S. Kuwabata and H. Yoneyarna, J. electrothem. Sot. 135, 1132 (1988). 8. G. Bidan et al., Mater. Sci. Forum 42, 51 (1989). 9. G. Bidan and B. Ehui, J. them. Sot. them. Commun., 1568 (1989). 10. K. Hyodo and M. Nozaki, Electrochim. Acta 33, 165 (1988). 11. K. Hyodo and M. Omae, Electrochim. Acta MS 311. 12. R. Kessel. G. Hansen and J. W. Schultxe. Ber. Bunsenges.‘phys. Chem. 92, 710 (1988). 13. J.-C. LaCroix and A. F. Diaz, Makromol. Chem., Macromol. Sym. 8, 17 (1987); J. electrochem. Sot. 135, 1457 (1988). 14. W.-S.‘ Wuang, B. D. Humphrey and A. G. MacDiarmid, J. them. Sot., Faraday Trans. 182, 2385 (1986).