A new iron(iii) 2,4,6-trimethylbenzenesulfonate (MSA) with composition [Fe(OH2)5(MSA)3] has been prepared from thereaction of Fe(OH)3·xH2O and three molar equivalents of 2,4,6-trimethylbenzenesulfonic acid and used as oxidant in thepreparation of highly conducting polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene) (PEDOT) films for the firsttime. PPy and PEDOT films grown on non-conducting overhead transparency (polyethylene terephthalate films) using avapour phase polymerization technique exhibited very high conductivities; 200 ± 20 S cm−1 for PPy and 1000 ± 80 S cm−1
for PEDOT.
Manuscript received: 14 August 2008.Final version: 13 January 2009.
Introduction
Since the discovery of conducting polymers by Shirakawaet al.,[1] a wide variety of electrically conducting polymershave been studied. Conducting polymers combine useful char-acteristics of metals, such as electrical conductivity, withthose of conventional polymers, such as low density andflexibility.[2–5] Polypyrrole (PPy) and poly(3,4-ethylenedioxy-thiophene) (PEDOT) have been the primary focus of researchfor many applications because of their ease of synthesis, highenvironmental stability, high contrast ratios, good electricalconductivity, and robustness.[6]
Conducting polymers can be readily prepared via chemicalor electrochemical oxidation. Synthesis of conducting polymersby electrochemical oxidation requires conductive substrates and,hence, it is not useful for applications where electronic function-alities are to be added to non-conductive substrates. Patterningof substrates is also not feasible using electrochemical oxidationbecause the polymerization takes place in the bulk of solution.Chemical synthesis can be achieved in solution, at an inter-face, or in the vapour phase.[7] For example, Bayer AG hassuccessfully commercialized an aqueous suspension of PEDOT/polystyrenesulfonate (Bayer P) prepared by chemical polymer-ization in the bulk solution but Greonendaal et al. have reportedthat spin casting of these PEDOT solutions produces films withconductivities of only 10 S cm−1.[8] However, PPy is difficult toprocess in this way, as it has the major disadvantage of beinginsoluble in most solvents.[7] Even dispersions, stabilized steri-cally or by manipulating charge, can be difficult to form becausePPy readily agglomerates owing to strong interactions betweenpolymer chains. As a consequence, vapour-phase polymeriza-tion (VPP) is considered to be the most suitable technique forpatterning of such conducting polymers.
Im et al.[9] have recently reported the use of oxidativechemical vapour deposition for growing PEDOT films with aconductivity of 700 S cm−1 using FeCl3, but this technique can-not be used for patterning of conducting polymers because themonomer and the oxidant are both introduced in the vapour phasein this technique, unlike the VPP described by Winther-Jensenet al.,[10] which can be used for patterning. In the latter two-stepprocess, oxidant film deposition followed by exposure to pyr-role vapour enables the growth of a uniform film of PPy on asubstrate.
Our aim was to develop a technique to print the oxidanton substrate surfaces by inkjet printing, and so the VPP tech-nique was considered to be ideal for our studies. Synthesisconditions like temperature, choice of oxidants, and solventsplay an important role in the conductivity of conducting poly-mers. For example, the synthesis of PPy at low temperature hasbeen reported to result in better conductivity.[11] Over the pastfew years, use of different oxidants such as iron(iii) chloride,[12]
pyridinium chlorochromate, tetraethylammonium tetrafluoro-borate,[20] and benzyl peroxide[21] have been used to preparePPy. However, to the best of our knowledge, none of the iron(iii)-based oxidants, in particular, has resulted in an exceptionalconductivity for PPy films deposited by VPP. The majority ofthese oxidants have in fact been used to synthesize PPy by thechemical polymerization technique.
The first studies of the polymerization of conducting poly-mers in the vapour phase were conducted by Mohammadi et al.at low pressure in 1986.[22] Over the past two decades, sev-eral papers have reported the synthesis of conducting polymers
using VPP.[10,23,24] However, most of the work in the area ofVPP has been carried out using FeCl3 as an oxidant. Recently,the use of iron(iii) tosylate (or p-toluenesulfonate) oxidant mar-keted by Bayer AG as Baytron CB-40 for synthesis of PEDOTand PPy by VPP has been reported.[10] Winther-Jensen et al.have been able to produce PEDOT with conductivity as high as1000 S cm−1 using iron(iii) tosylate[10] and this encouraged usto study the effect of varying the location, length, and num-ber of alkyl groups on the sulfonate anion of the iron(iii)p-alkylbenzenesulfonate oxidants on the conductivity of PPy.The synthesis of PPy in the presence of anionic surfactants,such as dodecylsulfonic acid or polystyrenesulfonic acid, hasbeen reported to improve the thermal stability and the stabil-ity of conducting polymers towards deprotonation.[24] Hencethe advantage of using iron(iii) p-alkylbenzenesulfonate as anoxidant for the synthesis of conducting polymers is the incorpo-ration of a surfactant anion with the iron(iii). This eliminates theneed for a surfactant in addition to the oxidant during the syn-thesis of polymer, a simplification that is an obvious advantage.Kudoh et al. concluded that the presence of an electron-donatinggroup, like a methyl in the sulfonate anion of the oxidant, canincrease the conductivity of the polymer.[25] Our previous studyon the effect of increasing the alkyl chain-length of iron(iii) p-alkylbenzenesulfonate on the conductivity of PPy synthesized byVPP showed that there was no correlation between increasingthe alkyl chain-length of the sulfonate anion and the conduc-tivity of PPy, but that the presence of an electron-donatingmethyl group in the para position of the benzene ring of theoxidant anion improved the conductivity of the PPy.[26] Giventhese findings, we have synthesized a new FeIII alkylbenzene-sulfonate oxidant, viz. iron(iii) 2,4,6-trimethylbenzenesulfonate(FeIIIMSA), which has electron-donating methyl groups in thepositions ortho and para to the sulfonate group on the benzenering. We have applied this new oxidant in the synthesis of PPyand PEDOT films by the VPP technique, achieving the highestreported conductivity for PPy films deposited by VPP.
Results and DiscussionSynthesis and Characterization of Iron(III)TrimethylbenzenesulfonateThe new oxidant, FeIIIMSA, was synthesized by the reaction ofhydrated iron(iii) hydroxide and the sulfonic acid in a ratio of1:3. Following drying under vacuum, the product powder wassparingly soluble in water and was difficult to recrystallize. Ele-mental analysis indicated that the compound was a simple aquaion salt with a composition of [Fe(OH2)5][C6H2(CH3)3SO3]3.The presence of only five water molecules per octahedral iron(iii)centre suggests that at least one sulfonate is coordinated tothe iron(iii) centre. The Fourier-transform (FT)-IR spectrumof FeIIIMSA showed asymmetric and symmetric vibrations ofthe sulfonate groups at 1100 to 1200 cm−1 and at 1016 cm−1,respectively and an O–H stretch close to 3400 cm−1. In ourprevious work, we found that the iron(iii) p-toluenesulfonatecomplex is binuclear, with the iron(iii) centres linked via anoxo-bridge, and exhibits a characteristic Fe–O–Fe stretch at833 cm−1.[15,27] This is absent in the IR spectrum of FeIIIMSA,consistent with the microanalysis data indicating a compositionof [Fe(OH2)5(C9H11SO3)3].
Synthesis and Characterisation of Polymer FilmsPPy and PEDOT films were prepared by a VPP technique onpolyethylene terephthalate (PET) films as described below or
in the literature[28] and characterized using scanning electronmicroscopy (SEM), X-ray photoelectron spectroscopy (XPS),Raman, and UV-visible spectroscopy.
SEM and XPS Analysis of Polymer FilmsThe PPy films (see Fig. 1a) prepared using iron(iii) trimethyl-
benzenesulfonate appeared much more homogeneous than thoseprepared using FeCl3 (see Fig. 1c). The surface morphology ofPEDOT film prepared using the new oxidant, as shown in Fig. 1b,was comparable with those reported in the literature.[10] Therewas no sign of crystallization on evaporation of the solvent fromthe iron(iii) trimethylbenzenesulfonate films, or following depo-sition of the PPy films, when compared with FeCl3 (see Fig. 1c)and other traditional iron(iii) oxidants. As a consequence, PPyfilms formed using the new oxidant had smoother and more uni-form surface morphology compared with the PPy films dopedwith commercial p-toluenesulfonate anions (Baytron CB-40).The XPS spectra of PPy and PEDOT films were in agreementwith those reported previously for films produced using otheriron(iii) sulfonate as oxidants (see Accessory Publication).
Conductivity MeasurementsThe surface resistances and thicknesses of PPy and PEDOT
films prepared using iron(iii) trimethylbenzenesulfonate weremeasured using a four-point probe technique and by SEM,respectively, allowing the calculation of conductivity. The con-ductivities given here were calculated by averaging two sets ofreadings, and were 200 (±20) S cm−1 and 1000 (±80) S cm−1
for PPy and PEDOT, respectively. Our results are compared withthe literature data for PPy and PEDOT by VPP in Fig. 2 andFig. 3, respectively.[29–32] Compared with PPy, there are few lit-erature data for PEDOT films synthesized byVPP at atmosphericpressure.
Relatively few oxidants have been trialled usingVPP.[13–16,18,20,23,28,33–40] The highest conductivities reportedfor this polymerization method for PPy and PEDOT films were100 S cm−1 and 1000 S cm−1, respectively, using iron(iii) tosy-late (Baytron CB-40) and iron(iii) chloride oxidant.[10,23] In ourlaboratory, we previously obtained a conductivity of 40 (±2)S cm−1 [26] for PPy produced with commercial iron(iii) tosy-late (Baytron CB-40) by VPP, which is close to the 50 S cm−1
reported by Winther-Jensen et al.[28] for the conductivity of VPPPPy using Baytron CB-40. To the best of our knowledge, theconductivity of PPy films produced with FeIIIMSA is twicethe highest value reported in the literature for PPy producedby VPP method.[23] For PEDOT, SEM examination indicatedhigh-quality films were obtained (see above) and the conduc-tivities matched the best reported to date in the literature forVPP-deposited PEDOT.[41–43]
Electroactivity and Electrochromic BehaviourThe cyclic voltammogram traces obtained from PPy and
PEDOT films made byVPP using FeIIIMSA were similar to whathas been reported in the literature,[10,33,44] indicating that thesefilms were highly electroactive (see Accessory Publication).
The UV-visible spectra of PPy film synthesized withFeIIIMSA (see Fig. 4) showed a peak at 420 nm, which is due tothe π–π∗ transition, and a significant absorption beyond 600 nmfor fully oxidized PPy film, which is a result of a free carrier tail.The reduced PPy film shows no absorbance in the visible regionof the spectrum.The PPy film was reduced at −0.5V versus satu-rated calomel electrode and the reduced yellow PPy film showed
Vapour-Phase Polymerization of Pyrrole and 3,4-Ethylenedioxythiophene 135
(c)
10 �mPPy/FeCI3_25 degrees
(a)
10 �mMSA
(b)
10 �mPEDOT – surface
Fig. 1. (a) Scanning electron microscopy (SEM) image of polypyr-role (PPy) film synthesized by vapour-phase polymerization (VPP) usingiron(iii) 2,4,6-trimethylbenzenesulfonate. (b) SEM image of poly(3,4-ethylenedioxythiophene) film synthesized by VPP using iron(iii) 2,4,6-trimethylbenzenesulfonate. (c) SEM image of PPy film synthesized by VPPusing iron(iii) chloride.
a strong absorption at 320 nm. The peak at 320 nm decreases andthe peak at 420 nm increases as the PPy is oxidized as reported byRam et al.[39] The UV-visible spectra of the PEDOT shown inFig. 5 show that when the film is reduced at −0.9V versusAg/AgCl, a dark blue colour is produced, which is associatedwith strong absorption at 750 nm. The reduced PEDOT film,however, is oxidized within a few seconds and gives rise to alight blue colour. Consequently, it is difficult to observe the dif-ference between the UV-visible spectra of reduced and oxidizedPEDOT. On switching to a potential of +0.8V, the film bleachesto a sky-blue colour and shows strong absorbance beyond700 nm due to the presence of bipolarons and a ‘metallic’ freecarrier tail.
Raman SpectroscopyThe Raman spectrum obtained for PPy, as shown in Fig. 6,
agrees with data reported earlier by us[26] and literaturereports.[45–47] The spectrum showed that the PPy was highlyconjugated. There was no evidence of sulfonate stretches inthe Raman spectra of PPy and PEDOT films, indicating thatthe Raman stretches observed are solely due to polymer. Thepresence of an enhanced peak at 1613 cm−1 is due to the C=Cbackbone stretch, resulting from dicationic activity (bipolarons)and the band at 1581 cm−1 is due to a C=C backbone stretchresulting from the presence of cationic species. The bands at1334 and 1383 cm−1 are due to asymmetrical C–N stretching.Two well-resolved bands at 1054 and 1083 cm−1 are due to C–Hin-plane bending associated with radical cations and radical dica-tions, respectively. Ring deformation due to cationic species canbe seen at 966 cm−1 and that due to dication species can beseen at 942 cm−1. The band at 1728 cm−1 is due to the pres-ence of carbonyl groups. As discussed in our earlier work,[26]
Raman and XPS spectra of PPy films synthesized with a seriesof iron(iii) alkylbenzenesulfonates indicated the presence of car-bonyl groups and this was proposed to be associated with thepresence of carboxylate anions, which might result from oxida-tion of 2-butanol or possibly due to the carbonyl stretches fromthe underlying PET substrate.
The Raman spectrum for a PEDOT film prepared usingFe(iii)-MSA/pyridine oxidant film (see Fig. 7) shows a band at1539 cm−1 is due to asymmetric Cα=Cβ stretches. This bandwas seen close to 1509 cm−1 as noted by Garreau et al.[38]
for VPP PEDOT synthesized in the absence of pyridine, but isfound to be shifted to 1539 cm−1 in the spectrum of our PEDOTfilm. The peak at 1425 cm−1 is due to symmetric Cα=Cβ(–O) stretching and is indicative of a high level of oxidationin the structure of PEDOT. A similar band at 1425 cm−1 wasfound for fully oxidized PEDOT film by Chau et al.,[45] andhence the presence of a band at 1425 cm−1 in our base-inhibitedPEDOT shows that the polymer is oxidized. A band arisingfrom the Cβ–Cβ stretch is seen close to 1365 cm−1 and Cα–Cα′(inter-ring) stretches are seen at 1267 cm−1. The absence ofCα–H and Cβ–H bending in the base-inhibited PEDOT synthe-sized in the present work is in accordance with bands observedin the spectrum of base-inhibited PEDOT synthesized usingiron(iii) tosylate by Winther-Jensen et al.[10] The absence ofCα–H and Cβ–H bending indicates a higher degree of conjuga-tion, hence higher conductivity in PEDOT. C–O–C deformationleads to a peak at 1094 cm−1, whereas oxyethylene ring deforma-tion is seen at 990 cm−1.The bands at 703 cm−1 and at 575 cm−1
are due to symmetric C–S–C ring deformation and oxyethylenedeformation, respectively.
136 P. Subramanian et al.
0 50 150100 200 250
Conductivity [S cm�1]
Oxi
dant
sIron(III) ethylbenzenesulfonate
Iron(III) benzenesulfonate
Ref. [26]
Ref. [26]
Iron(III) pyridinesulfonate
Iron(III) pyridinemethanesulfonate
Iron(III) morpholinepropanesulfonate
Iron(III) dodecylbenzenesulfonate
Iron(III) 2-acrylamido-2-methylpropanesulfonate
Iron(III) p-toluenesulfonate
Iron(III) p-toluenesulfonate(Baytron)
Iron(III) chloride
Ref. [27]
Ref. [27]
Ref. [27]
Ref. [26]
Ref. [26]
Ref. [26]
Ref. [26]
Ref. [32]
This workIron(III) trimethylbenzenesulfonate synthesized and VPP in our laboratory
Fig. 2. Conductivities of polypyrrole films synthesized using different oxidants by vapour-phase polymerization (VPP).
0 200 600400 800 1000 1200
Conductivity [S cm�1]
Oxi
dant
s
Iron(III) chloride VPP PEDOT filmRef. [53]
Iron(III) p-toluenesulfonate VPP PEDOT film
Iron(III) trimethylbenzenesulfonate VPP PEDOT film
Ref. [33]
Synthesized in our laboratoryThis work
Fig. 3. Conductivities of poly(3,4-ethylenedioxythiophene) (PEDOT) films synthesized using differentoxidants by vapour-phase polymerization (VPP).
1.1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
1
320 520
OxidizedNeutral
720 920 1120 1320 1520 1720 1920
Wavelength [nm]
Abs
orba
nce
[a.u
.]
Fig. 4. UV-visible spectra of polypyrrole film grown on over-head transparency by vapour-phase polymerization using iron(iii) 2,4,6-trimethylbenzenesulfonate. Film is yellow in the neutral and black is theoxidized state.
1.9
1.7
1.5
1.3
1.1
0.9
0.7
0.5
0.3315 515 715
OxidizedNeutral
915 1115 1315 1515 1715 1915
Wavelength [nm]
Abs
orba
nce
[a.u
.]
Fig. 5. UV-visible spectra of poly(3,4-ethylenedioxythiophene) filmgrown on overhead transparency by vapour-phase polymerization usingiron(iii) 2,4,6-trimethylbenzenesulfonate. Film is red in the neutral and blackin the oxidized state.
Vapour-Phase Polymerization of Pyrrole and 3,4-Ethylenedioxythiophene 137
2500
2000
1500
1000
861
942
966 10
83
1187
1255 13
34 1383
1532
1581
1613
1728
1054
500
800 1000 1200
Wavenumber [cm�1]
Inte
nsity
[a.u
.]
1400 1600
0
Fig. 6. Raman spectrum of polypyrrole film synthesized by vapour-phasepolymerization using iron(iii) 2,4,6-trimethylbenzenesulfonate.
5000
4000
3000
2000
526 57
5
703 86
0 990
1094 11
56 1267
1365
1425
1539
1572
941
1000
600 800 1000 1200
Wavenumber [cm�1]
Inte
nsity
[a.u
.]
1400 1600 1800
0
Fig. 7. Raman spectrum of poly(3,4-ethylenedioxythiophene) filmsynthesized by vapour-phase polymerization using iron(iii) 2,4,6-trimethylbenzenesulfonate.
Conclusions
Iron(iii) 2,4,6-trimethylbenzenesulfonate has been prepared forthe first time and used as an oxidant to synthesize highlyconducting PPy and PEDOT films by theVPP technique. Ramanspectroscopy and XPS analysis of the films indicated that the PPyfilms are highly conjugated and oxidized. The PPy and PEDOTfilms were seen to be electrochromic and showed electrochem-ical responses typical of PPy and PEDOT films synthesized byVPP. The conductivities of VPP PPy films (200 ± 20 S cm−1)were twice the best previously reported, whereas those forVPP PEDOT films (1000 ± 80 S cm−1) were similar to the bestreported in the literature.[2] The presence of three electron-donating methyl groups in the para and ortho positions on thearomatic ring of the sulfonate anion has a positive effect onfilm properties, in keeping with the findings for films depositedusing iron(iii) p-toluenesulfonate, cf. iron(iii) benzenesulfonate.The methyl substituents increase the electron density on thenegatively charged sulfonate group and this could be aidingthe formation of highly conductive PPy and PEDOT films. AsFeIIIMSA, like other iron(iii) aromatic sulfonate salts, does not
crystallize readily, it can form smooth films when coated on asubstrate and this oxidant, unlike FeCl3, overcomes the issuesof crystallization on the surface of the substrate. The ability todeposit smooth oxidant films contributes to the formation of PPyfilms whose surface morphology is very homogeneous. In thisvein, it has recently been observed[42,43] that the electrical prop-erties of VPP PEDOT are independent of the anion present inthe material, but very dependent on the anion used as ligand inthe FeIII oxidant. The formation of uniform, highly conductivePPy and PEDOT films by VPP could derive from the unifor-mity of the FeIIIMSA oxidant films but also from the improvedtemplating properties of the trisusbtituted aromatic sulfonateanion, noting again that this salt produces more conductivefilms than both the benzenesulfonate and p-toluenesulfonatesalts.
ExperimentalMaterialsPyridine, 2,4,6-trimethylbenzenesulfonic acid, pyrrole, iron(iii)chloride hexahydrate, n-butanol, and ethanol were pur-chased from Sigma–Aldrich, Australia. The monomer 3,4-ethylenedioxythiophene (Baytron M) was obtained from BayerAG. All chemicals were used as received. Microanalysis ofFeIIIMSA was carried out by Campbell Microanalytical Ser-vices, University of Otago, New Zealand.
Synthesis of Iron(III) TrimethylbenzenesulfonateIron(iii) trimethylbenzenesulfonate was synthesized by the reac-tion of Fe(OH)3 with three molar equivalents of the sulfonic acid,as described previously for related iron(iii) sulfonate salts.[26]
Briefly, ferric hydroxide was prepared by slowly adding 11.1 g(0.28 moles) of NaOH to 75 mL water and then adding the solu-tion with vigorous stirring to 25.0 g (0.09 moles) of FeCl3·6H2Odissolved in 350 mL of water. After 1 h, the entire reactionmixture was filtered through a medium-porosity glass sinteredfunnel. The collected amorphous brown solid was rinsed severaltimes with a large amount of water. The freshly prepared fer-ric hydroxide was suspended in 175 mL of ethanol and 65.5 g(0.27 moles) of 2,4,6-trimethylbenzenesulfonic acid, dissolvedin 100 mL of ethanol, were added slowly over a period of 5 min.The reaction mixture was gently warmed to 50◦C, and stirredvigorously for 3 h to complete the reaction of the Fe(OH)3. Theorange-red solution was then cooled at room temperature andfiltered to remove any insoluble impurities.The filtrate was evap-orated and the remaining oil product placed in a crystallizingdish. The reaction product was further dried in a vacuum ovenat 50◦C and 13.34 kPa pressure. The dried product was then fur-ther washed with water and dried in a vacuum desiccator (yield35 g, 78%).
Elemental analysis for [Fe(OH2)5][C6H2(CH3)3SO3]3,Fe1C27H43S3O14 (Mw 742.9 g mol−1) (Calculated: C 44.7,H 5.7, S 13.2, Fe 7.7%. Found: C 44.9, H 5.7, S 13.3, Fe 7.8%).
Synthesis of Polypyrrole (PPy)VPP was carried out with a simple set-up consisting of a sealedflask with monomer in the bottom, sitting on a hot-plate–stirrer.Approximately 8 g of FeIII oxidant, such as FeIIIMSA or iron(iii)chloride was added to 15 mL of 2-butanol and heated at 50◦Cto dissolve the oxidant and form a solution at 40 wt-%. The oxi-dant was applied to a non-conducting overhead transparency(PET) by spin-coating at 2000 rpm and dried at 70◦C for ∼90 s.The coated substrate was then exposed to pyrrole vapour in the
138 P. Subramanian et al.
reaction vessel where it changed from yellow to green to blackin a few minutes. The PET substrate was kept in the cham-ber for 10 min, air-dried to remove unreacted pyrrole monomer,and then washed thoroughly in ethanol to remove any remain-ing iron(ii) and iron(iii) salts. The same procedure was used toprepare films using the iron(iii) chloride oxidant solution. Thewashed PPy films were stored in plastic containers for furtheranalysis.
Synthesis of Poly(3,4-ethylenedioxythiophene)PEDOT films were synthesized by VPP according to the methodgiven by Winther-Jensen et al.[28] for base-inhibited reactionof 3,4-ethylenedioxythiophene (EDT) monomer with iron(iii)tosylate, which gives PEDOT with good conductivity. Pyridine(0.5 mL, 0.05 moles) was added to a 40 wt-% FeIIIMSA solutionprepared as described above. The iron(iii) sulfonate–pyridinemixture was spin-coated on PET films and heated on a hot plateat 70◦C until the solvent had evaporated. The oxidant–pyridine-coated PET substrate was then exposed to the EDT monomerat 50◦C until polymerization was complete (30–40 min). ThePEDOT film obtained was then air-dried to remove unreactedmonomer. The black PEDOT films were washed thoroughly inethanol for 10–15 min to remove remaining iron(ii) and iron(iii)salts.After washing, the PEDOT films turned light blue and thesewere stored in plastic containers for further analysis.
Characterization of PPy and PEDOT FilmsThe PPy and PEDOT films were characterized using Ramanspectroscopy (JOBIN Yvon Horiba Raman spectromodelHR800) and X-Ray photoelectron spectroscopy (Kratos XPS).Film thickness was measured from cross-sections using aPhilips XL 30 field emission SEM and surface conductiv-ity was measured using the standard four-point probe tech-nique. Film conductivities, measured by the four-point probemethod, were reproducible to within the experimental uncer-tainties (±20 S cm−1 for PPy and ±80 S cm−1 for PEDOT)when the deposition procedures outlined above were repeated.The UV-visible spectra of the PPy films were measured underabsorption mode from 320 to 2000 nm using a Cary 300 UV-visible spectrophotometer. The morphology of the PPy filmsproduced on iron(iii) trimethylbenzenesulfonate-coated PETwas examined using SEM. FT-IR analysis of the iron(iii) alkyl-benzenesulfonate salts was carried out on KBr pellets of eachsalt using a Perkin–Elmer Spectrum 2000 (Beaconsfield, Berk-shire, UK). The spectra were acquired in absorption modeusing a resolution of 4 cm−1 and 32 scans over a range of4500–400 cm−1.
The Raman spectra were collected with a spectral resolutionof 1.5 cm in the backscattering mode with 632.8 nm intensitylight from a helium–neon laser. A Guassian–Lorentzian fittingfunction was used to obtain band position and intensity.The inci-dent laser beam was focussed on the spectrum surface through a100× object lens. Samples showing fluorescence were analysedfor 30-s time intervals in a dark room with a D2 filter and otherswere analyzed for 10-s time intervals with a D1 filter.
XPS analyses were performed with a KRATOS AnalyticalAXIS-HSi spectroscopy using a monochromated Al Kα X-raysource operated at 12 kV and 12 mA emission current. The emis-sion was nominally 0◦ with respect to the surface normal and thechamber pressure was maintained between 2 and 8 × 10−9 kPa.Survey spectra were acquired to determine all elements presenton the surface of the materials. High-resolution spectra were
then recorded for carbon (C) in order to obtain more specificdata regarding chemical structure (i.e. oxidation state). Spectrawere obtained at two different locations on each sample (at 0◦emission). The mean atomic ratios were calculated for each sam-ple and emission angle and the standard deviation determinedas a measure of compositional variation. The systematic erroris estimated to be between 5 and 10%. The relative sensitivityfactors were C 1s 0.250, O 1s 0.660, N 1s 0.420, and Si 2p 0.180.
Accessory Publication
Details of the XPS analysis and cyclic voltammetry for PPy andPEDOT films produced by VPP are available on the journal’swebsite.
AcknowledgementsThe authors acknowledge Monash University for the award of a MonashGraduate Scholarship to P.S., and the Co-operative Research Centre SmartPrint for financial support. We are grateful to Mr Mark Greaves for hisassistance with the SEM measurements.
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