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Electrochimica Acta 122 (2014) 296– 302

Contents lists available at ScienceDirect

Electrochimica Acta

j our nal homep age : www.elsev ier .com/ locate /e lec tac ta

Towards conducting inks: Polypyrrole–silver colloids

Mária Omastováa, Patrycja Boberb, Zuzana Morávkováb,∗, Nikola Perinkac,Marie Kaplanovác, Tomás Syrovy c, Jirina Hromádkováb, Miroslava Trchováb,Jaroslav Stejskalb

a Polymer Institute, Slovak Academy of Sciences, 845 41 Bratislava, Slovakiab Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, 162 06 Prague 6, Czech Republicc University of Pardubice, Faculty of Chemical Technology, 532 10 Pardubice, Czech Republic

a r t i c l e i n f o

Article history:Received 16 July 2013Received in revised form 6 November 2013Accepted 6 November 2013Available online 20 November 2013

Keywords:Conducting inksPolypyrroleColloidsSilver

a b s t r a c t

The oxidation of pyrrole with silver nitrate in the presence of suitable water-soluble polymers yieldscomposite polypyrrole–silver colloids. The polypyrrole–silver nanoparticles stabilized with poly(N-vinylpyrrolidone) have a typical size around 350 nm and polydispersity index 0.20, i.e. a moderatepolydispersity in size. Similar results have been obtained with poly(vinyl alcohol) as stabilizer. The effectof stabilizer concentration on the particle size is marginal. In the present study, several types of stabi-lizers have been tested in addition to currently used poly(N-vinylpyrrolidone). Transmission electronmicroscopy and optical microscopy revealed the gemini morphology of polypyrrole and silver colloidalnanoparticles and confirmed their size and size-distribution determined by dynamic light scattering.The use of colloidal dispersions provides an efficient tool for the UV–vis and FT Raman spectroscopiccharacterization of polypyrrole, including the transition between polypyrrole salt and correspondingpolypyrrole base. The dispersions were used for the preparation of coatings on polyethylene terephtha-late foils, and the properties for polypyrrole–silver composites have been compared with those producedfrom polypyrrole colloids alone.

© 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Polypyrrole (PPy) is one of the conducting polymers which has,in addition to conductivity, also other attractive properties, suchas biocompatibility [1,2], stability under in-vivo conditions [3],reversible protonation, and redox behavior [4]. The oxidations ofpyrrole with various oxidants, such as ammonium peroxydisulfate[4] or iron(III) salts [5], leading to PPy have been optimized in theliterature with respect to conductivity and morphology.

During last years, there has been growing interest in thecomposites of conducting polymers and noble metals, such asPPy–silver composites [6–11]. The direct polymerization of pyr-role using silver nitrate as oxidant in aqueous medium is the mostefficient way to obtain conducting polymer–silver composite in asingle reaction step (Fig. 1) [12–17].

The processability of such composites is difficult and, forthat reason, various application forms have been sought. Among

∗ Corresponding author. Institute of Macromolecular Chemistry, Academy of Sci-ences of the Czech Republic, Heyrovsky Sq. 2, 162 06 Prague 6, Czech Republic;Tel.: +420 296 809 379, fax: +420 296 809 410.

E-mail address: moravkova@imc.cas.cz (Z. Morávková).

them, colloidal dispersions are promising [18], as they can beprocessed by various printing techniques [19–22]. Conducting-polymer colloids are produced when the oxidation of the respectivemonomer, such as aniline or pyrrole, has been carried out inthe presence of stabilizers [18], typically suitable water-solublepolymers [23] or inorganic nanoparticles, e.g., nanocolloidalsilica [24].

The formation of PPy–silver colloids has been reported whenpyrrole was oxidized with silver nitrate in the presence ofpoly(N-vinylpyrrolidone) [6–9,25]. The composite colloidal par-ticles had a silver core of 90–300 nm size and a PPy shell ofcomparable thickness. In a single case, silver nanoparticles of10–12 nm size were prepared separately and subsequently usedas seeds [7] but it is not clear if they were really neededfor the success of preparation. Poly(N-vinylpyrrolidone) hasalso been used in other syntheses but the formation of col-loidal dispersions has not been reported [15,16,24,26,27]. ThePPy–silver colloids stabilized by other polymers than poly(N-vinylpyrrolidone), except for starch [28,29], have not beendescribed so far. In the present communication, several poten-tial stabilizers have been tested in this respect and resultingcolloids have been compared with those stabilized with poly(N-vinylpyrrolidone).

0013-4686/$ – see front matter © 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.electacta.2013.11.037

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NH

NHNH NH

NH

4 n + 10 n AgNO3

NO3

NO3

HNO3+ 8 n+ 10 n Ag

n

Fig. 1. Pyrrole is oxidized with silver nitrate to polypyrrole, metallic silver and nitricacid are by-products.

2. Experimental

2.1. Oxidation of pyrrole

Pyrrole (Acros Organics, USA) was purified by distilla-tion under reduced pressure and stored at 4 ◦C. Pyrrole wasoxidized with silver nitrate (p.a., Centralchem, Slovakia) in aqueoussolutions of various water-soluble polymers, such as poly(N-vinylpyrrolidone) (PVP; type K-60, Fluka, Switzerland; solutioncontaining 50 wt.% PVP, molecular weight 160,000), poly(vinylalcohol) (PVAL; type 22 000, Fluka, Switzerland, molecular weight22,000; degree of hydrolysis 97.5–99.5 mol%), poly(ethylene oxide)(Polyox WSR-205, BDH Chemicals, UK, molecular weight 600,000),methylcellulose (Methocel MC, Fluka, Switzerland), hydroxyethyl-cellulose (Natrosol, type 250 GR, Hercules, Aqualon Division, USA),hydroxy-propylcellulose (Klucel, type 99-JF, Hercules, AqualonDivision, USA), and poly(acrylamide-co-acrylic acid) (Aldrich,Czech Republic, molecular weight 5,000,000). Inorganic stabilizer,nanocolloidal silica (Ludox AS-40, DuPont product supplied byAldrich, USA, 40 wt.% suspension in water) has also been included inthe studies. In a typical experiment, pyrrole (0.25 ml = 0.242 g) wasdissolved in the solution of a polymeric stabilizer to 50 mL, silvernitrate (1.22 g) was separately dissolved in water to 25 mL, and bothsolutions were mixed to start the oxidation of pyrrole. The molarconcentration of pyrrole was 3.6 mM and the oxidant-to-monomermole ratio was 2. The concentration of stabilizers varied between0.5–5.0 wt.%. The reaction mixture was gently stirred with a mag-netic bar for one hour and then was left for five days at rest. Theresulting dark-brown colloidal dispersion was then stored. Refer-ence samples of PPy dispersions without silver were prepared bythe oxidation of 3.2 mM pyrrole with equimolar concentration ofammonium peroxydisulfate and 3 wt.% of PVP or PVAL.

2.2. Characterization

The particle size was determined with a dynamic light-scattering apparatus, an AutoSizer Lo-C (Malvern, UK). The colloidal

dispersions were diluted with water before such experiments.At least five measurements of particle sizes have been done andthe results were averaged. The polydispersity index (PDI), a rela-tive width of the particle-size distribution, has also been obtainedby assuming the logarithmic-normal distribution of particle sizes.Morphology was assessed with a transmission electron microscope(TEM) JEOL JEM 2000 FX and with optical attachment for NicoletFTIR spectrometer having 50× objective magnification. For spec-troscopic measurements, the colloids were diluted 50× with 1 Mmethanesulfonic acid for the spectra of PPy salts or with 1 M ammo-nium hydroxide for PPy bases. The UV–visible spectra of PPy–silvercolloids were recorded with a Lambda 20 spectrometer (PerkinElmer, UK). FT Raman spectra were recorded on a Thermo Nico-let 6700 FTIR Spectrometer with a silicon-coated calcium fluoridebeam-splitter and NXR FT-Raman module (3993 cm−1–50 cm−1)with an air-cooled-indium-gallium-arsenide detector. NIR excita-tion laser with a wavelength 1064 nm and 180◦ sample geometrywas used. An energy dispersive X-ray analysis (EDAX) spectrumwas recorded with a FEI Quanta F200, USA, for elemental surfaceanalysis.

2.3. Coatings

Original PPy–silver colloids were deposited on transparentflexible polyethylene terephthalate foil for ink-jet printing (PET;Melinex ST 504, DuPont Teijin Films; thickness 175 �m, surfaceresistivity 1014 � sq−1, surface free energy 45.4 mN m−1, sur-face roughness 1.5 nm). Thin films of the stabilized PPy colloidswere prepared with an automatic film applicator Elcometer 4340(Gamin, Czech Republic) using a Mayer Rod coating system (wirerod size No. 4, wet thickness of film 10.2 �m). The films were driedunder laboratory conditions at 23 ◦C and relative humidity 40% for1 h. Optical micrographs of dry films were acquired with an opticalmicroscope (Bresser Erudit, Bresser, Germany, 5 Mpx CMOS camerasystem) and the conductivity was estimated by two-point method.For the conductivity assessment, the samples were cut into 4 × 4mm2 squares. In order to minimize the impact of imperfect contactbetween the measuring tip of multimeter and tested film, contactpoints were created on the film using carbon paste. The thicknessof prepared films was determined with a profilometer Dektak XT(Bruker, UK). The thickness was evaluated from cross-sectional pro-files of scratched films. The estimated thickness was used for thecalculation of conductivity.

3. Results and discussion

3.1. Effect of stabilizer concentration

The size of PPy–silver colloidal particles was little depend-ent on the concentration of polymer used for their stabilization,poly(N-vinylpyrrolidone) or poly(vinyl alcohol) (Table 1). Theaverage particle diameter was 300–400 nm and the particles

Table 1The particle size and polydispersity index (PDI), and their standard deviations, of colloidal dispersions obtained by the oxidation of 3.6 mM pyrrole with 7.2 mM silver nitratein the presence of various concentrations of stabilizers, poly(N-vinylpyrrolidone) or poly(vinyl alcohol).

Stabilizer concentration, wt.% Poly(N-vinylpyrrolidone) Poly(vinyl alcohol)Size, nm PDI Size, nm PDI

0.5 362 ± 16 0.27 ± 0.06 468 ± 25 0.47 ± 0.031.0 381 ± 10 0.20 ± 0.02 347 ± 20 0.22 ± 0.031.5 372 ± 11 0.20 ± 0.04 326 ± 24 0.19 ± 0.082.0 330 ± 12 0.16 ± 0.05 321 ± 25 0.17 ± 0.062.5 325 ± 12 0.17 ± 0.03 320 ± 36 0.29 ± 0.103.0 337 ± 11 0.21 ± 0.02 315 ± 20 0.22 ± 0.054.0 303 ± 11 0.14 ± 0.02 346 ± 33 0.38 ± 0.175.0 382 ± 12 0.28 ± 0.03 322 ± 12 0.29 ± 0.03

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Fig. 2. Transmission electron micrographs of the composite PPy–silver colloids prepared in the presence of (A) 2.5 wt.% poly(N-vinylpyrrolidone), and (B) 5.0 wt.% poly(vinylalcohol).

were moderately polydisperse, PDI ≈ 0.20, on a relative scalefrom monodisperse particles (PDI = 0) to extreme polydispersity(PDI = 1). This is in accordance with the similar results on relatedpolyaniline colloids stabilized by these polymers [23] and with theproposed concept of particle formation [30]. During this process,aniline oligomers are expected to adsorb on stabilizer chains, andsubsequently start the growth of conducting-polymer chains thatcreate the body of a colloidal particle. For that reason, the parti-cle size is controlled rather by molecular weight of the conductingpolymer than by the type, molecular weight, or the concentration ofthe stabilizer. Some minimum concentration of the stabilizer, how-ever, must be available to accommodate the conducting polymer.Otherwise, colloidal particles become accompanied by macroscopicprecipitate [23]. This should be avoided if the colloid is intended forthe use in printing formulations.

3.2. Morphology

The colloidal particles have a gemini structure rather than thecore–shell morphology (Fig. 2B). This means that the PPy part(shadowed) is associated with silver particle (dark) but does notwrap it. The gemini structure, in our opinion, reflects the fact thatthe reaction between pyrrole molecule and silver ion is based ona redox process, i.e. on the transfer of an electron from the formerto the latter. For such a transfer, the direct contact between thereacting species is not necessary, and the electron is transferredthrough a growing conducting PPy–silver particle, which is in thecontact with both reacting molecules dissolved in the reaction mix-ture. This concept has also been used to explain the polymerization

of aniline in frozen reaction mixtures, in ice, where the diffusionof reacting species was restricted but the redox reaction still tookplace [30–32]. Both PPy and silver parts of the particles, however,have to have an access to the reactants. For that reason, a geministructure seems to be preferred over the core–shell type [28,29].

Even optical microscopy can be conveniently used for the obser-vation of colloidal nanoparticles (Fig. 3). The PPy–silver particles arecolored and provide good optical contrast with respect to surround-ing medium. Although the details of particles cannot be recognized,the globular shape is confirmed. The micrographs also demonstratethe absence of large particles or aggregates in the micrometer-sizerange. This is important when applications, such as the preparationof conducting inks, are considered.

3.3. Effect of stabilizer type

The use of other water-soluble polymers has also led to sta-ble colloidal PPy–silver dispersions (Table 2). With poly(ethyleneoxide), colloidal particles were accompanied by larger objects,such as silver crystals (Fig. 4A) and the average particle size thuscould not be determined (Table 2). The same result applies to theuse of hydroxyethylcellulose. For methylcellulose (Fig. 4B), how-ever, the particles were relatively uniform (Table 2) and similar inshape and size to those stabilized with poly(vinyl alcohol) (Fig. 2B).When using poly(acrylamide-co-acrylic acid) for the stabilization,the morphology seems to be more complex and based on aggre-gated fractal structures (Fig. 4 C). This is reflected by larger particlesize but still low polydispersity index (Table 2). The similar resulthas also been obtained with hydroxypropylcellulose (Table 2). Each

Fig. 3. Optical micrographs of the PPy–silver colloids prepared in the presence of 3.0 wt.% of (A) poly(N-vinylpyrrolidone) and (B) poly(vinyl alcohol).

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Fig. 4. Transmission electron micrographs of the composite PPy–silver colloids prepared in the presence of (A) poly(ethylene oxide), (B) methylcellulose, (C) poly(acrylamide-co-acrylic acid), and (D) nanocolloidal silica Ludox AS-40.

polymer stabilizer has thus to be assessed individually with respectto the stabilizing efficiency of PPy–silver colloids, and no generalconclusions can be drawn.

Colloidal silica, as a representative of inorganic particulate sta-bilizers, had low stabilizing efficiency. Silica particles of 36 nmdiameter [24] are clearly visible on micrographs (Fig. 4D). Despitesmall and uniform silver particle sizes, below 50 nm, observed asdark spots, much larger aggregates have been detected by dynamiclight scattering and manifested themselves in high polydispersityindices (Table 2). They seem to be formed by silica particles glued byPPy–silver to large polydisperse aggregates (Table 2), without theformation of defined objects. Inorganic stabilizers do not possessfilm-forming properties and their use in applications is limited.

It has to be stressed that the observations reported in this sectionare based on single concentrations of stabilizers. Under differentstabilizer concentrations or reaction conditions, the results mightalso be different, and these stabilizers should not be dismissed atthis stage.

3.4. UV–visible spectra

Polypyrrole is insoluble in any solvent and therefore its opticalspectra are difficult to record. The preparation of thin polypyrrolefilms [33,34] or especially colloidal dispersions [35] thus offers anefficient tool to monitor the absorption spectra of this importantpolymer (Fig. 5).

Table 2The particle size and polydispersity index (PDI) of colloidal dispersions obtained bythe oxidation of 3.6 mM pyrrole with 7.2 mM silver nitrate in 3 wt.% solutions ofvarious water-soluble polymers or in 5 wt.% nanocolloidal silica.

Stabilizer Size, nm PDI

Hydroxyethylcellulose (a) (a)Hydroxypropylcellulose 995 ± 38 0.52 ± 0.07Methylcellulose 561 ± 22 0.29 ± 0.01Poly(acrylamide-co-acrylic acid) 914 ± 24 0.34 ± 0.05Poly(ethylene oxide) (a) (a)Nanocolloidal silica 1403 ± 181 0.78 ± 0.16

a Dynamic light scattering indicated the presence of large particles and the averageparticle size could not be determined.

The PPy–silver dispersions can be diluted with acidic or alkalinemedium. In the former case, PPy is present as a salt, in the latter asa base (Fig. 6). Salt and base forms of PPy have been discussed inthe literature less frequently [4,33,36–43], while a similar salt–basetransition in polyaniline has been analyzed in detail [30,37]. This isprobably due to the fact that the transition in polyaniline is asso-ciated with the change in colour from green to blue [44] and thereduction in the conductivity by more than nine orders of magni-tude [45]. While the smaller reduction in the conductivity has beenreported for PPy after the conversion from salt to base [4], colourchanges are marginal, and PPy remains brown. The reduction ofthe absorption in the red part of spectra, however, is clearly visible.It is assumed that the absorption bands with the maxima at 540and 654 nm are associated with the �–polaron transitions. A moredetailed analysis is needed in future because the present spectramay also be affected by plasmonic resonance of silver nanoparti-cles.

10008006004000.0

0.5

1.0

PVP

PVAL

PVAL 406 540

432

Abs

orba

nce

(a.u

.)

Wavelength / nm

654

PVP

Fig. 5. UV–visible spectra of PPy–silver colloids prepared in 3 wt.% solutions of PVPor PVAL and diluted 50× with 1 M methanesulfonic acid (solid lines) or 1 M ammo-nium hydroxide (dashed lines). Wavelengths corresponding to the local maxima aregiven at the individual spectra.

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A

A

NHNH NH

NH

n

− 2 n HA

n

NHNHN

N

Fig. 6. Salt–base transition in PPy: Under alkaline conditions, PPy salts converts toPPy base. HA is an arbitrary acid.

3.5. Raman spectra

Colloidal PPy dispersions can conveniently be used also for otherspectroscopic studies, such as FT Raman spectroscopy (Fig. 7). Alsoin this case, after the dilution with acidic or alkaline medium, PPysalt and base forms can be separately characterized. FT Ramanspectra of aqueous PPy–silver colloids were recorded with exci-tation laser wavelength 1064 nm, which is in the resonance withthe absorption band of PPy dication constitutional unit [46]. This,and a possible surface enhancement on silver nanoparticles, affectsthe band positions and intensities.

Polypyrrole salts. The band at 1577 cm−1 for PVP-stabilized and1583 cm−1 for PVAL-stabilized colloid (overlap of ring vibration ofboth neutral and radical cation or dication bearing units [33,47–49])is less intensive for the former that for the latter (Fig. 7). The smallerband at 1487 cm−1 is attributed to C N and C–C stretching in thepyrrole ring [47,49]. The group of bands connected with C–H andN–H bending [49], C–C stretching of neutral units and antisymmet-ric C–H bending [47,49] is located at 1370, 1313/1328 (PVP/PVAL)and 1238 cm−1. Broad band between 1090 and 1050 cm−1 is associ-ated with C–H, N–H and ring out-of-plane (1090 cm−1) and in-plane(1050 cm−1) deformations with possible contribution of the vibra-tion of sulfonic or nitrate anions [17,46,47,49]. A sharp peak at937 cm−1 belongs to in-plane deformations of the pyrrole ring in

4006008001000120014001600

860982

922

1043

1245

1605

1210

14001305

968

937

1238

1050

13281370

1313

1487

1583

1090

MSA

(PPy salt - Ag) + PVP

(PPy salt - Ag) + PVAL

(PPy base - Ag) + PVAL

Inte

nsit

y

Wavenumber / cm-1

(PPy base - Ag) + PVP

FT Raman,

exc. 1064 nm

1577

Fig. 7. Raman spectra of PPy–silver colloids prepared in the presence of 3 wt.% ofPVP and PVAL. The spectrum of 1 M methanesulfonic acid (MSA) is included.

1 10 100200

300

400

500

Size

/ nm

Time / day

Fig. 8. Time dependence of the particle size of colloidal PPy–silver dispersions pre-pared in the presence of 0.5 wt.% PVP.

a dication-bearing unit [33,47,49] (Fig. 6). This peak has a shoul-der at 968 cm−1 assigned to in-plane ring-deformations in neutralrings [38,41].

Polypyrrole bases. In the spectra of PPy bases, no differencesintroduced by the different stabilizers have been observed (Fig. 7).The differences between the spectra of PPy salts and PPy bases,however, are marked. The bands of PPy base are located at1605 cm−1 (C C stretching in the pyrrole ring [47]), 1487 cm−1

(C N stretching in the pyrrole ring [39]), 1305 cm−1 (C–H bendingcombined with C–N stretching [39]) with a shoulder at 1400 cm−1

(vibration of ammonium cation), 1210 cm−1 (antisymmetric C–Hdeformations) with a shoulder at 1245 cm−1, 1043 cm−1 (C–Hbending [39] with possible contribution of methanesulfonic acid),and 922 cm−1 (C–H out of plane deformations [33]) with smallside bands at 982 cm−1 (C–C deformations in neutral rings [38,39])and 860 cm−1.

The spectra of PPy–Ag colloids differ significantly in intensi-ties of individual bands from the FT Raman spectra of PPy basesobserved by Jenden et al. [33]. In present case, the intensities arelower for higher wavenumbers and higher for lower wavenumbers;Jenden et al. observed slightly opposite effect. This is connectedwith the elastic scattering from colloidal particles.

3.6. Colloidal stability

The colloidal stability belongs to important issues required bythe applications. A colloidal dispersion with the lowest content ofPVP, 0.5 wt.%, was selected for the stability test. During about 20days after preparation, the particle size decreased (Fig. 8) as wellas the polydispersity index. This means that some of the disper-sion particles were entangled and were gradually liberated. Thedispersions were stable during 250 days and no marked trend inthe particle size was observed. After 300 days, however, a colloidalinstability was observed and a macroscopic precipitate appeared.It is reasonable to assume that the colloidal dispersions preparedin the presence of larger concentration of stabilizer would be morestable.

3.7. Deposition of coatings

The PPy and the composite PPy–silver colloids stabilized byPVAL and PVP were deposited on PET foil. The micrographs ofthe coatings demonstrated significant differences in the morphol-ogy and homogeneity (Fig. 9). The composite PPy–silver particlesformed smooth homogenous films composed of individual col-loidal particles (Fig. 9A,B). On the contrary, the films cast from PPycolloids without silver were inhomogeneous; this applies espe-cially to PVP-stabilized PPy colloid (Fig. 9C), which nevertheless

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Fig. 9. Optical micrographs of the composite PPy–silver colloids prepared in the presence of (A) PVP and (B) PVAL and the reference PPy colloids stabilized with (C) PVP and(D) PVAL.

Table 3The comparison of the conductivity and thickness of the prepared PPy films.

Colloid Stabilizer Thickness, �m Conductivity, S cm−1

PPy Poly(N-vinylpyrrolidone) 22.3 3.45 × 10−5

Poly(vinyl alcohol) 4.79 1.39 × 10−4

PPy–silver Poly(N-vinylpyrrolidone) 7.15 2.33 × 10−5

Poly(vinyl alcohol) 2.05 1.22 × 10−4

indicated a certain degree of order dependent on the direction oflayer deposition on the substrate. The PPy colloids stabilized withPVAL (Fig. 9B,D) indicated significantly better film-forming prop-erties than PVP-stabilized colloids (Fig. 9A,C). PVAL-stabilized PPycolloids, however, suffered from the lower adhesion of dry films tothe PET foil.

The measurement of the specific conductivity showed that thepresence of silver in the PPy colloids does not have a significantimpact on the resulting conductivity of the films (Table 3). Thisis rather disappointing but understandable result, because the vol-ume fraction of silver in the coatings is deeply below the percolationlimit needed for the efficient conduction. The PPy colloids stabilizedwith PVAL were slightly more conducting than those prepared inthe presence of PVP.

3.8. Film composition

The elemental composition in PPy–silver thin films stabilizedby PVP and the presence of silver was confirmed by energy disper-sive X-ray analysis (EDAX) (Fig. 10). The PPy–silver film contained16.5 wt.% of silver. This is a low value, because the oxidation of pyr-role with silver nitrate should provide a PPy–composite containing73.6 wt.% silver [17]. The presence of PVP in the film, and the factthat EDAX characterizes rather the surface than the body of the film,are responsible. A low conductivity of the films (Table 3) is thus alogical consequence.

Fig. 10. Energy dispersive X-ray analysis (EDAX) spectrum of PPy-silver film stabi-lized by PVP.

4. Conclusions

Colloidal dispersions of polypyrrole–silver nanoparticles havebeen prepared by the single-step oxidation of pyrrole with silvernitrate in the solutions of poly(N-vinylpyrrolidone) or poly(vinylalcohol) as stabilizers. The particle sizes were in the range300–400 nm, and independent of stabilizer concentration. Particleswere composed of gemini polypyrrole and silver parts. The colloidswere stable for at least hundreds days. Other stabilizers, such asmethylcellulose, hydroxypropylcellulose, or poly(acrylamide-co-acrylic acid), have also proved to be able to stabilize colloids but theparticle sizes were larger and particles more polydisperse in size.Composite polypyrrole–silver colloids proved to be a suitable formfor the UV–visible and FT Raman spectroscopic characterization,

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including the salt–base transition in polypyrrole. The preparedfilms of PPy were conducting but the conductivity was low, of theorder of 10−5–10−4 S cm−1, and the contribution of silver to theconductivity was marginal because its content is below the per-colation threshold. Composite PPy–silver colloids had significantlybetter film-forming properties than colloids without silver.

Acknowledgement

The authors wish to thank the Technological Agency of the CzechRepublic (TE01020022) and Czech Science Foundation (13-00270S)for the financial support. This work was also supported within theproject VEGA 02/0149/14.

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