Conducting polymer and ionic liquid: Improved thermal stability of the material – A spectroscopic study

Accepted Manuscript Conducting polymer and ionic liquid: Improved thermal stability of the material – a spectroscopic study Miroslava Trchová, Ivana Šeděnková, Zuzana Morávková, Jaroslav Stejskal PII:

S0141-3910(14)00249-3

DOI:

10.1016/j.polymdegradstab.2014.06.012

Reference:

PDST 7378

To appear in:

Polymer Degradation and Stability

Received Date: 24 April 2014 Revised Date:

6 June 2014

Accepted Date: 15 June 2014

Please cite this article as: Trchová M, Šeděnková I, Morávková Z, Stejskal J, Conducting polymer and ionic liquid: Improved thermal stability of the material – a spectroscopic study, Polymer Degradation and Stability (2014), doi: 10.1016/j.polymdegradstab.2014.06.012. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT Conducting polymer and ionic liquid: Improved thermal stability of the material – a spectroscopic study Miroslava Trchová,* Ivana Šeděnková, Zuzana Morávková, Jaroslav Stejskal

Prague 6, Czech Republic

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Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, 162 06

*Corresponding author: Miroslava Trchova, Tel.: +420 291809381; fax: +420 291809410, e-

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mail: [email protected]

ABSTRACT

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Green polyaniline hydrochloride film was converted to a blue polyaniline base and exposed to an ionic liquid, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate. The ionic liquid was found to interact with polyaniline base in similar manner like an acid, and the green colour corresponding to conducting form was recovered. The resulting material maintained its “salt” character even above 200 °C, while the deprotonation of standard polyaniline hydrochloride

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took place under similar conditions. The state and the changes in molecular structure have been assessed by UV-visible and FTIR spectra. The experiments demonstrate a strong interaction between polyaniline and ionic liquid, which results in the conductivity and

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improved thermal stability of resulting material.

Keywords: Polyaniline; Conducting polymer; Ionic liquid; FTIR spectroscopy; Thermal

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stability

1. Introduction

Polyaniline (PANI) ranks among the most studied conducting polymers. Many papers

have concentrated mainly on improvement of conductivity and the control PANI morphology, which includes especially nanotubes and nanofibres [1–3]. Application of conducting polymers in biomedicine is one of the new and promising research directions. This concerns especially the neural [4–6] and cardiac [7,8] or brain cells and tissues, which transfer the electric signals. The monitoring of vital functions or the electrical stimulation of living species belongs to attractive research targets. The application of conducting polymers in 1

ACCEPTED MANUSCRIPT biosciences has to cope with three problems: (1) reduction of toxicity and improvement of biocompatibility, (2) mixed electronic and ionic conduction, and (3) good level of conductivity under physiological conditions, i.e. at neutral or slightly alkaline media. Biocompatibility studies suggests that polyaniline alone is not toxic [9,10] but the reaction intermediates included in the product or acid constituting the salt with PANI may have

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undesirable effects [10,11]. Mixed electronic and ionic conductivity would be helpful because conducting polymers would be used as transducers at interfaces between biological material and electronic devices [12]. There are studies which suggest the presence of such mixed conductivity in polyaniline [13–15], especially when the polymer operates not in aqueous

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media and not in dry state, as it is typical of most studies. Classical PANI salts, such as PANI hydrochloride, loose their conductivity above pH 4–5 as they convert to non-conducting PANI base. The protonation of PANI with polymeric [16–22] or hydrophobic acids [23] or

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the modification with ionic liquids [24] are the promising ways for the solution of this task. The present study concentrates on the formation and stability of new PANI-based systems comprising ionic liquids.

Ionic liquids represent an equally interesting class of materials [25,26] due to their non-volatility, ionic conductivity, stability, and applicability in pharmacology and

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biosciences. The combination of ionic liquids with polymers in general [27,28], and with conducting polymers in particular [24], thus offers the possibility for the preparation of new materials with properties potentially prospective also in biomedicine. The preliminary experiments have shown that the conductivity of PANI base exposed to ionic liquid, 1-ethyl-

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3-methylimidazolium trifluoromethanesulfonate, increased by ten orders of magnitude, from 10−11 to 10−1 S cm−1. This means that the chemical interaction between both species took place. The doping of PANI base in imidazolium ionic liquids was interpreted as a specific

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interaction of the quinonoid moiety of the PANI base with the imidazolium ring [29]. An interaction between ionic liquids and conducting polymers has also been reported for polypyrrole [30] or poly(3,4-ethylenedioxythiophene) [31]. The thermal stability of ionic liquids is well known. The introduction of such liquid to PANI thus raises the question if the stability of resulting system will also be improved in the comparison with common PANI salt. The dissolution of PANI emeraldine base in imidazolium ionic liquids was investigated by spectroscopic techniques in [29]. The stabilization of pernigraniline salt by synthesis in ionic liquids was proved by using FTIR spectroscopy [32]. Spectroscopic methods have proved to be a powerful tool in the characterization of conducting polymers [33–37], and FTIR spectroscopy has been used for this purpose in the present study. 2

ACCEPTED MANUSCRIPT 2. Experimental

2.1. Preparation

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Thin PANI films were deposited in situ during the polymerization of 0.2 M aniline hydrochloride with 0.25 M ammonium peroxydisulfate [38] on glass or silicon substrates immersed in the reaction mixture [39]. The PANI hydrochloride films were converted to PANI base in 1 M ammonium hydroxide (Fig. 1), dried and immersed into the ionic liquid, 1-

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ethyl-3-methylimidazolium trifluoromethanesulfonate (EMImTFM; 99 %; IoLiTec Ionic Liquid Technologies GmbH, Germany) for five days at room temperature. Colour of films changed from green to blue after the deprotonation and again to green in ionic liquid. The

H N

H AN

t l a s I N A P

−

A H 2

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H N

H N A

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supports were rinsed with acetone and kept in desiccator over silica gel.

e s a b I N A P

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H N

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H N

N

N

Fig. 1. Conducting polyaniline salt is deprotonated in alkaline media to a non-conducting polyaniline base. The base can be again reprotonated with acids (HA) to corresponding salts.

The conductivity of PANI has earlier been determined on pellets prepared from the

powders. Standard PANI hydrochloride had a conductivity 4 S cm–1 and PANI base 8×10–9 S cm–1

[40]

Ionic

conductivity

of

ionic

liquid,

1-ethyl-3-methylimidazolium

trifluoromethanesulfonate, is 8.3×10−3 at 20 °C [41] and of its aqueous solutions of the order of 10−2 S cm–1 [42]. Polyaniline "reprotonated" with ionic liquid had a conductivity 0.43 S cm–1. 3

ACCEPTED MANUSCRIPT 2.2. Spectroscopic characterization

UV–visible spectra of the films grown on glass supports were recorded with a Lambda 20 spectrometer (Perkin Elmer, UK). Some films were heated to 170 or 236 °C in an

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oven, the heating was switched off and the films were left to cool to room temperature. Fourier-transform infrared (FTIR) spectra of the films deposited on silicon windows were recorded in the range of 650–4000 cm–1 at 256 scans per spectrum at 4 cm–1 resolution using a fully computerized Thermo Nicolet NEXUS 870 FTIR Spectrometer using DTGS detector. Samples deposited in-situ on silicon windows were heated from 20 oC to 200 oC in

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the temperature-controlled cell. The spectra were measured every 10 oC. The temperature increase and stabilization take in average 13 min for each spectrum. After measurements,

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spectra were corrected for the moisture and carbon dioxide in the optical path. An absorption subtraction technique was used to remove the spectral features of silicon wafers. Golden GateTM Heated Diamond ATR Top-Plate (MKII Golden Gate single reaction ATR system) was applied for the supporting measurements of pure ionic liquids. The ionic liquid placed on diamond crystal in Golden Gate single reflection ATR system was heated

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from 30 oC to 200 oC. The drop of the liquid was heated up by 10 °C in 10 min. After heating, the samples were cooled to the initial temperature and the spectra were measured.

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3. Results and discussion

3.1. UV–visible spectra

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The salt–base transition in emeraldine form of PANI is well known. The emeraldine

salt, obtained after the oxidative polymerization of aniline in acidic media, deprotonates above pH ≈ 4–5, loses acid molecule, and converts to PANI base (Fig. 1). This process is associated with the change in conductivity from the order of 1 S cm−1 to 10−10 S cm−1 and the change in colour from green to blue. The latter process manifests itself by the shift of absorption maximum [43,44] from ≈ 800 nm (polaron–π transition) to ≈ 600 nm (π–π* transition in quinonedimine units) and by the disappearance of the shoulder at ≈ 420 nm (π– polaron transition) [45,46] (Fig. 2).

4

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original PANI film 1.0

PANI-EMImTFM 0.5

0.0

600

800

1000

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400

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Absorbance

PANI base

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Wavelength, nm

Fig. 2. UV–visible spectra of original PANI hydrochloride film obtained after polymerization. spectrum of corresponding PANI base, and the spectrum of this base after interaction with the ionic liquid, EMImTFM.

The salt–base transition is fully reversible (Fig. 1) and the PANI base can be

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reprotonated with various acids to corresponding salts [47]. It was rather surprising to observe, that green form is recovered also after the interaction of PANI base with an ionic liquid (Fig. 2). This type of interaction, however, must be different, as ionic liquids do not

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contain any proton.

The thermal stability of PANI assessed by the changes in conductivity depends on the type of counter-ion: PANI hydrochloride rates to unstable forms [48], PANI sulfate to most

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stable salts [49]. Generally, the temperature stability of thin PANI films is lower compared with bulk material compressed to pellets [33] and PANI salts deprotonate to corresponding bases [50,51]. After the exposure to temperature above 200 °C, the blue shift of the maximum at 800 nm is clearly visible in the present case (Fig. 3) but the deprotonation is still not complete as evidenced by the residual shoulder in 420 nm region.

5

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original PANI film

0.5 PANI film after 236 °C

0.0

400

600

800

1000

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Wavelength, nm

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Absorbance

1.0

Fig. 3. The changes in the UV–visible spectrum of PANI hydrochloride film after heating to

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236 °C.

The PANI films which were exposed to the ionic liquid behave in different manner. The absorption maximum at 800 nm corresponding to the presence of polarons in PANI structure even slightly shifts to higher wavelengths (Fig. 4). There is no deprotonation observed because, obviously there are no protons which could be liberated from PANI. The

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thermal stability is thus improved compared with standard salts. Some reduction of absorption

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in red region, however, indicates the possibility of starting decomposition changes.

20 °C

1.0

AC C

Absorbance

PANI-EMImTFM films

0.5

0.0

170 °C 236 °C

400

600

800

1000

Wavelength, nm

Fig. 4. The UV–visible spectrum of PANI associated with ionic liquid and its changes after the heating to 170 or 236 °C. 6

ACCEPTED MANUSCRIPT The interaction of the ionic liquid with PANI backbone is far from being understood [29]. We can speculate that imidazolium moiety contains a hydrogen atom that is sufficiently acidic to simulate a protonation of imine nitrogens in PANI (Fig. 5a). Such cases have been reported, and the salts of PANI with 2,4,6-trinitrophenol (picric acid) [47,52] or 3-nitro-1,2,4triazol-5-one (NTO) [38] serve as examples.

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The creation of a hydrogen bond between the N–H group in the polyaniline models and the O–S group in the sulfonic acid models increases the ability of the phenyl–nitrogen backbone to transfer electron density [53]. It has recently been reported that the thermal stability of PANI salts depends, in addition to acid strength, also on the hydrogen bonding

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[49]. When the PANI salts contain counter-ions with oxygen atoms that produce hydrogen bonds with amino groups in PANI chain, the thermal stability becomes enhanced (Fig. 5b). For that reason, polyaniline sulfate maintains most of its conductivity when heated to 125 °C

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for several weeks, while PANI hydrochloride may lose the conductivity within few hours. The similar concept probably applies to the present case and the hydrogen bonding between trifluoromethanesulfonate counter-ion in ionic liquid (Fig. 5) and PANI is responsible for the observed stability at elevated temperature. The authors assume that both mechanisms are

H N

H N aaaa

O O S O bbbb

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H F C F

F

3

H C 2 H C N

N

3

H C

N H

N

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3

3

F O

H C 2 H C N

N

H C

F C S O

F O

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operational simultaneously.

Fig. 5. Possible interactions of an ionic liquid with PANI: (a) "Acidic" hydrogen in ionic liquid can "protonate" imine nitrogens in PANI backbone. (b) Hydrogen atom from secondary amino group in PANI may produce a hydrogen bond with oxygen atom in the counter-ion of ionic liquid. 7

ACCEPTED MANUSCRIPT 3.2. FTIR spectra of standard PANI films

Infrared spectroscopy is well suited for the studies of hydrogen bonding and related interactions. The spectrum of original PANI hydrochloride before heating (spectrum Ps, 20 o

C, in Fig. 6) exhibits a broad absorption band at wavenumbers higher than 2000 cm−1, which

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is characteristic of conducting emeraldine form of PANI, and polaron band is responsible for this broad absorption. The main peaks of PANI base at 1594 cm−1 and 1506 cm−1 are redshifted to 1582 and 1496 cm−1 in the spectrum of PANI hydrochloride. The absorption band at 1306 cm−1 is strengthened due to π-electron delocalisation in the polymer induced by

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protonation. The band characteristic of conducting protonated form is observed at about 1245 cm−1. It has been interpreted as C–N+• stretching vibration in the polaron structure. The spectrum of the PANI hydrochloride exhibits a strong and broad band centred at 1145 cm–1,

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which has been assigned to the vibration mode of the –NH+= structure [34].

FTIR on Si

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AC C 4000

1496

1582

3500

1306

1378 o

Ps, 20 C

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Absorbance

3070 2948 3244 2922 3374 2846

1145

1245 1040 803

o

1506

o

Ps, 20 C (after 200 C) 1594 1166

830

o

Pb, 20 C

3000

2500

2000

−1

1500

1000

Wavenumbers, cm

Fig. 6. The spectrum of standard PANI hydrochloride film before (Ps, 20 oC) and after the heating to 200 °C (Ps, 20 oC (after 200 oC)) and the comparison with the spectrum of PANI base (Pb, 20 oC).

8

ACCEPTED MANUSCRIPT The infrared spectrum of the film of PANI hydrochloride after heating to 200 oC (spectrum Ps, 20 oC (after 200 oC) in Fig. 6) reveals the deprotonation of the sample. The most significant change in the spectrum is the decrease of the polaronic band above 2000 cm–1 connected with the deprotonation of the PANI salt to the base. The other more subtle changes have been observed in the region of molecular vibrations under 2000 cm–1 and can also be

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mainly assigned to the changes connected with deprotonation. The main peaks of quinonediimine and benzene ring-stretching deformations are slightly red-shifted. The characteristic peak of PANI base at 1378 cm−1 appeared. The bands at 1306 and 1245 cm−1 together with the peak at 1145 cm–1 decreased. All these changes are connected with thermal

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deprotonation of PANI hydrochloride [33]. This process is different from chemical deprotonation as it is follows from the comparison with the spectrum of the film of PANI base (spectrum Pb, 20 oC, in Fig. 6) described earlier [33]. The main peaks at 1594 cm−1 and 1506

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cm−1 correspond to a quinone and benzene stretching ring deformations, respectively. The band at 1378 cm−1 is attributed to a C-N stretching in the neighborhood of a quinonoid ring. The 1306 cm−1 band is assigned to C–N stretch of secondary aromatic amine whereas, in the region of 1010–1170 cm−1, the aromatic C–H in-plain bending modes are usually observed. At 830 cm−1 out-of-plane deformation of C–H on 1,4-disubstituted ring are located. The peak observed in the spectrum of PANI hydrochloride at 1040 cm–1 after the heating to 200 °C

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(spectrum Ps, 20 oC (after 200 oC) in Fig. 6) is missing in the spectrum of chemically deprotonated PANI base. It belongs most probably to the SO3– group on sulfonated aromatic ring [35]. PANI film obtained by oxidation of aniline with ammonium peroxydisulfate

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contains mainly hydrogen sulfate counter-ions due to the presence of sulfuric acid which is a by-product of this reaction [2]. In addition, some amount of sulfonated aniline oligomers is

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also present in the final film [2]. These are removed from the film during chemical deprotonation with ammonium hydroxide, but not during thermal deprotonation.

3.3. Temperature dependence of FTIR spectra of standard PANI films

The thermal ageing of PANI hydrochloride has been studied in detail by FTIR spectroscopy (Fig. 7) and it is in good agreement with the decrease in conductivity of the sample [54] and with previously published results [33,34]. The gradual deprotonation of the film occurs continuously from the first stages of the heating. Contrary to the chemical deprotonation of PANI hydrochloride by ammonium hydroxide, the thermal deprotonation is not complete at the investigated temperature range. 9

ACCEPTED MANUSCRIPT FTIR on Si o

t [ C] =

3374

20 40 60 80 100 120 140 160 170 180

2948 3070 2922 2846

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Absorbance

3244

190

o

20 (after 200 C)

4000

3500

3000

2500

2000

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200

−1

1000

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Wavenumbers, cm

1500

Fig. 7. Temperature dependence of the infrared spectra of the PANI hydrochloride film. In the region above 2500 cm–1 the peaks located at 2948, 2922 and 2846 cm–1 correspond to a strong interchain NH+···N hydrogen bonding between regularly aligned PANI

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chains. These peaks partly disappeared during heating (Fig. 7). The maximum at 3244 cm–1 can be attributed to the secondary amine N–H+ stretching vibrations hydrogen bonded with Cl– [55]. Participation of hydrogen sulfate HSO4– and sulfate SO42– counter-ions, which are probable [49].

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present due to the protonation with sulfuric acid, a by-product of the oxidation reaction, is

The study of the ageing of PANI base using FTIR spectroscopy confirmed the

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presence of the transition at the temperature around 80 °C [34]. This feature is an inherent property of PANI and is not influenced by the nature of protonating acid. Below this temperature, ageing is slower than above it. We can speculate that this is associated with the "melting" of hydrogen bonds and consequent vulnerability of chains to the changes in molecular structure.

3.4. FTIR spectra of PANI films "reprotonated" with ionic liquid

The exposure of PANI base to ionic liquid leads to the changes in the infrared spectrum of original PANI base. Some of them are typical for protonation (Fig. 8), which 10

ACCEPTED MANUSCRIPT confirm the consequent electron redistribution over the PANI chain. However, the nature of the interaction of PANI base with ionic liquid has to be different as ionic liquid is aprotic, i.e. it has no proton available. The interactions based on hydrogen bonding (Fig. 5) are thus likely. We can speculate that the original intermolecular bonding between imine and amine groups in neighbouring chains of PANI chains [55] is replaced with (a) the bonding of imine

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nitrogens to "acid" hydrogen in at imidazolium heterocycle (Fig. 5a) and (b) the bonding of hydrogen in amino groups to oxygen atoms in trifluoromethanesulfonate counter-ion of ionic liquid (Fig. 5b). The former process is responsible for the "protonation-like" interaction, the second for the increased stability [49] illustrated below.

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The broad absorption band at wavenumbers above 2000 cm–1 which confirms the presence of unpaired electrons on PANI chains is observed in the infrared spectrum of PANI base exposed to ionic liquid (Fig. 8, spectrum PbIL, 20 oC). The red shift of the main bands of

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quinonediimine and benzene ring-stretching deformations to 1572 and 1497 cm−1 supports this observation. The increased absorption band at 1306 cm–1 with a shoulder at 1340 cm–1, the band at 1245 cm–1 interpreted as a C–N+• stretching vibration in the polaron structure, and the prominent 1155 cm–1 band assigned to the vibration mode of the –NH•+– structure corresponding to π-electron delocalization are all observed in the spectrum of PANI base

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exposed to ionic liquid. A small peak observed at 1378 cm–1 due to the C─N stretching vibration in the neighbourhood of a quinonediimine ring is still preserved in the spectrum of sample of PANI base exposed to ionic liquid. This indicates that either not all imine nitrogen

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limited.

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have been associated with imidazolium hydrogens, or the π-delocalization of electrons is

11

ACCEPTED MANUSCRIPT FTIR on Si

3245 3157

1245

3115

1155

Absorbance

3080

1279 1028

1378

o

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818 883 752 702

o

3500

3000

2500

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PbIL4, 20 C (after 200 C)

IL4 on ATR

4000

1574 1497

o

PbIL4, 20 C

2000

−1

1500

1000

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Wavenumbers, cm

Fig. 8. The spectrum of PANI "reprotonated" with ionic liquid before (PbIL, 20 oC) and after heating to 200 °C (PbIL, 20 oC (after 200 oC)). The spectrum of ionic liquid alone is shown

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for comparison (IL on ATR).

Only the sharp peak assigned to the symmetric SO3 stretching vibrations of sulfo group at 1028 cm−1 and smaller peak of CF3 stretching vibrations in trifluoromethane moiety at 752 cm−1 are well distinguished in the spectrum of PANI base after interaction with ionic

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liquid. Other bands of neat ionic liquid (Fig. 8, spectrum PbIL, 20 oC), such as the strong bands at 1252/1225 cm−1 of antisymmetric stretching vibrations of sulfonic group, the band at

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1149 cm−1 of the asymmetric CF3 stretching vibrations with possible contribution of imidazolium cation vibrations, are observed in the spectrum of PANI base exposed to ionic liquid, but they are overlapped with the bands characteristic of protonated PANI. This confirms that the ionic liquid became an integral part of PANI film. The presence of two peaks situated at 3150 and 3114 cm−1 belonging to the imidazolium ring-stretching vibrations in the spectrum of PANI base–ionic liquid system support the interaction of the ionic liquid with PANI base (Fig. 5a). The hydrogen bonding interactions are observed in the spectra for wavenumbers above ca 2800 cm−1. The bonding of hydrogen atom in amine group of PANI base with oxygen atoms of SO3 group in trifluoromethanesulfonate anion (Fig. 5b) is documented by the broad 12

ACCEPTED MANUSCRIPT band centred at 3255 cm–1 (Fig. 8, spectrum PbIL, 20 oC). The peaks located at 2948, 2922 and 2846 cm–1, corresponding to the strong interchain N–H···N hydrogen bonding between amino and imino groups in regularly aligned PANI chains of PANI hydrochloride, are missing in the spectrum of PANI base exposed to ionic liquid because they were replaced with new hydrogen bonds to ionic liquid.

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The infrared spectrum of PANI base exposed to ionic liquid after heating to 200 oC (spectrum PbIL, 20 oC, after 200 oC, in Fig. 8) corresponds to the partly “deprotonated” sample. The smaller decrease of the band above 2000 cm–1 and the red-shift of main peaks of quinonediimine and benzene stretching ring deformations to 1574 and 1497 cm−1 signifies

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that the PANI film exposed to ionic liquid is more stable that the standard film of PANI hydrochloride. The shape of the spectrum on the region of C–N+• stretching vibrations (three maxima at 1279, and 1245 cm−1) and in the region of the vibrations of –NH+= structure (one

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maximum at 1155 cm−1) show that the interaction between PANI base and ionic liquid was weakened but still persists (Fig. 8, spectrum PbIL, 20 oC, after 200 oC).

3.5. Temperature dependence of FTIR spectra of PANI films "reprotonated" with ionic liquid

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The evolution of thermal ageing of PANI base exposed to ionic liquid demonstrates its higher thermal stability in comparison to PANI hydrochloride (Fig. 9). Till the temperature about 100 oC the spectrum does not change. Then the gradual loss of interaction occurs. At 200 oC, the broad absorption band above 2000 cm–1 is still well observed, and corresponds

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approximately to the state of PANI hydrochloride at 100 oC. It should be noted that the changes in the infrared spectrum of pure ionic liquid measured on ATR crystal are very small

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and they are reversible, i.e. no damage of the ionic liquid occurs.

13

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FTIR on Si t [ C] =

20 110 140 160 170 180 190 200

o

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o

Absorbance

3255 3157 3115 3080

4000

3500

3000

2500

SC

20 (after 200 C)

2000

−1

1500

1000

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Wavenumbers, cm

Fig. 9 Temperature dependence of the infrared spectra of the film of PANI base "reprotonated with ionic liquid".

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4. Conclusions

Non-conducting films of blue polyaniline base were found to interact with an imidazolium ionic liquid and to produce a green conducting "salt". The spectroscopic characterization suggests that the interaction between the PANI and ionic liquid is based on

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the hydrogen bonding of two types: (1) a proton-like bonding of "acidic" hydrogen atom at imidazolium heterocycle to imine nitrogen atoms in PANI chain, and (2) the bonding of

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hydrogen atoms in amino groups of PANI to oxygen atoms in ionic liquid counter-ion. These bonds replace the bonding between hydrogen atom in amino groups to imino nitrogen atoms in PANI base. The PANI "salt" with ionic liquid produced in this way is thus conducting and more stable at temperatures elevated to 200 °C than standard PANI hydrochloride films.

Acknowledgments

The financial support of the Czech Science Foundation (P205/12/0911) gratefully acknowledged. Dr Elena Tomšík is thanked for the preparation of the samples containing the ionic liquid and for stimulating discussions. 14

ACCEPTED MANUSCRIPT References

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