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Synthetic Metals 183 (2013) 69– 72

Contents lists available at ScienceDirect

Synthetic Metals

journa l h om epage: www.elsev ier .com/ locate /synmet

ynthesis of polyaniline/clay conducting nanocomposites

.F. Baldissera ∗, J.F. Souza, C.A. FerreiraAPOL/PPGEM, Universidade Federal do Rio Grande do Sul, BP 15010, 91501-970 Porto Alegre, RS, Brazil

r t i c l e i n f o

rticle history:eceived 4 July 2013ccepted 24 September 2013vailable online 22 October 2013

a b s t r a c t

Nanomaterials have been considered as highly promising materials for various technological applications.In engineering, polymer nanocomposites are a new class of composite materials, where a clay or fillerwith nanometric dimensions is dispersed in a polymer matrix at low concentration or volume. Whenadded in quantities below 5% in the nanocomposites, clay cause a significant increase in these properties,

eywords:anocompositeonductive polymersolyanilinelayontmorillonite

such as mechanical, optical, magnetic barrier, and especially permeability and flammability resistance. Inthis context, this work aimed to obtain the polymeric nanocomposites of polyaniline (PAni) with differentcommercial clays (Cloisite Na+, 10A, 15A, 20A and 30B). The preparation of PAni and montmorillonite(PAni-MMT) nanocomposites was performed by in situ polymerization of aniline in acidic media (HCl).Electrical conductivity measurements, FT-IR, TGA and X-ray diffraction were some of the techniques usedto characterize the nanocomposites.

. Introduction

The use of the prefix “nano” to the designation of some materi-ls means that they have at least one dimension in the nanometerange, which is less than 100 nm [1]. Nanomaterials have beenonsidered as highly promising materials for various technologicalpplications.

The appropriate combination of two chemically distinct com-onents leads to formation of organic–inorganic hybrid materialsith different properties from those that originated and constitute

n alternative for the production of new multifunctional materi-ls with wide application. In engineering, polymer nanocompositesre a new class of composite materials, where a clay or filler withanometric dimensions is dispersed in a polymer matrix at low con-entration or volume [2,3]. These nanocomposites have receivedreat attention in academic and industrial sectors, representing theatest advancement in science and technology. The interest in theeld of nanotechnology is the special properties shown by theseaterials, not only because they make possible to obtain properties

quivalent to the traditional composites, but also exhibit specialroperties unique.

The clays are more commonly employed and when addedn quantities below 5% in nanocomposites, impart a signifi-ant increase in material properties, such as mechanical, optical,

agnetic, barrier, and especially permeability and flammability

esistance [4,5]. Clays are naturally hydrophilic, making it difficulto interact and obtain a homogeneous mixture with the polymer

∗ Corresponding author. Tel.: +55 51 33089418; fax: +55 51 33089414.E-mail address: alebaldissera@hotmail.com (A.F. Baldissera).

379-6779/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.synthmet.2013.09.022

© 2013 Elsevier B.V. All rights reserved.

matrices. The dispersion of clay in a polymeric matrix is obtainedby compatibilizing agents such as alkylammonium ions [6].

Preparation of nanocomposite polymer is performed by threemain ways: in situ polymerization, intercalation of the polymerfrom a solution and intercalation in the melt state [7]. Amongthe methods used for the addition of such fillers, only a smallnumber of studies in the literature describes the preparation ofthese materials by in situ polymerization. This polymerization isbased on the nanocomposite synthesis by growth of polymer chainsinside the galleries of a silicate, where the catalyst (or monomer) isanchored. In this context, this work aimed to obtain and character-ize polymeric nanocomposites of polyaniline (PAni) with differentcommercial montmorillonite (MMT) clays (Cloisite Na+, 10A, 15A,20A and 30B), thereby linking the properties offered by nanofillerwith the properties of conducting polymers.

2. Experimental

2.1. Synthesis of PAni-MMT nanocomposites

PAni-MMT nanocomposites were prepared by in situ polymer-ization of aniline in acidic medium (HCl). Firstly the MMT clay wasdried at 80 ◦C for 24 h to remove moisture. Further the clay wasadded to a 1 M HCl solution and sonicated for 30 min with the assis-tance of an ultrasound probe. Following, the monomer was addedand the solution was sonicated for another 30 min to promote thereplacement of inorganic ions by molecules of aniline between the

lamellae of the clay. A 1 M HCl solution containing the oxidizingagent [(NH4)2S2O8] was added dropwise to the solution containingthe monomer and clay under constant stirring. The polymerizationof aniline was carried out at temperatures between −4 and 0 ◦C, for

70 A.F. Baldissera et al. / Synthetic Metals 183 (2013) 69– 72

; (b) P

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Fig. 1. FTIR spectra of (a) PAni/HCl

h. The PAni-MMT obtained was filtered using porous glass funnelG5, under low pressure to speed up the process. The green pow-er obtained was washed with distilled water and finally dried inven at 60 ◦C for 24 h.

.2. Characterization of nanocomposites

Electrical conductivity measurements, FT-IR, thermogravimet-ic analysis (TGA), X-ray diffraction and transmission electronicroscopy (TEM) were some of the techniques used to charac-

erize the nanocomposites.

. Results and discussion

.1. FT-IR analysis

Fig. 1 shows the infrared spectra for PAni/HCl pure, PAni-MMTa+ and PAni-MMT 15A.

Fig. 2. TGA curves of MMT-Na+, PAni-MMT Na+, PA

Ani-MMT Na+; (c) PAni-MMT 15A.

The PAni/HCl spectra show two strong absorption bands at 1560and 1475 cm−1 attributed to the C C stretching of aromatic ringgroups quinoids (Q) and benzenoid (B) respectively. These valuesare similar to those previously reported by other authors [8,9]. Theband at 1300 cm−1 is assigned to the stretching of C N H bondsand that at 1134 cm−1 to the formation of polarons H+N Q NH+.As shown, the bands present in the spectrum of PAni/HCl are alsopresent in the spectra of PAni-MMT Na+ and PAni-MMT 15A, con-firming the formation of the conducting polymer even with theaddition of clay.

For the other nanocomposites with different clays the formationof conducting polymer with similar spectra to that of PAni/HCl hasbeen observed.

3.2. Thermogravimetric analysis (TGA)

This technique was used to obtain thermal behavior of the poly-mers. Fig. 2 shows the TGA curves for MMT-Na+, PAni-MMT Na+,

ni-MMT 15A, PAni-MMT 20A and PAni/HCl.

thetic Metals 183 (2013) 69– 72 71

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A.F. Baldissera et al. / Syn

Ani-MMT 15A, PAni-MMT 20A and PAni/HCl. The first thermalvent at TGA curves are observed at about 80 ◦C for all samplesnd is attributed to water loss of the polymers.

In the TGA thermogram of PAni/HCl a second event starting atbout 175 ◦C can clearly be seen, which can be associated withhe evolution of the acid dopant and degradation of oligomers.he third event in the thermogram starts around 300 ◦C and isssociated with a structural rearrangement due to breaks at thends of the polymer chains. The fourth event, starting at approx-mately 450 ◦C, is associated with degradation of the polymerhains [10].

The events observed for nanocomposites PAni-MMT Na+, PAni-MT 15A and PAni-MMT 20A are very similar to the pure polymer,

ince the polymer is the same for all the nanocomposites, i.e.Ani/HCl. Similar behavior was observed for the nanocompositeshere the clay added was MMT 10A and 30B.

The thermogravimetric analysis indicates that the nanocompos-tes synthesized can be used in applications where the temperatures below about 200 ◦C, which is the degradation onset temperaturef the polymers.

.3. Electrical conductivity

Electrical conductivity was measured by four points method11]. The conductivity of the PAni/HCl was 83 S cm−1. For theanocomposites the electrical conductivity was 62 S cm−1 for PAni-MT obtained from clays Na+, 15A and 20A and 61 S cm−1 for

Ani-MMT obtained from clays 10A and 30B.It was observed that the addition of clay led to a small decrease

n conductivity, as expected, due to the presence of insulat-ng charges between the polymer chains. However, it can betated that the nanocomposites still have an excellent electricalonductivity.

Fig. 4. Micrographs nanocomposites (a) PAni-MMT Na+; (b) P

Fig. 3. X-ray diffraction patterns.

3.4. X-Ray diffraction

Fig. 3 shows the X-ray diffraction patterns obtained for the clayMMT-Na+ and polymers PAni/HCl and PAni-MMT Na+. The maincharacteristics signs of MMT-Na+ are situated at 2� = 7.45◦ and2� = 19.75◦ [12]. Note that the diffractogram of PAni-MMT Na+ isvery similar to the pure polymer (PAni/HCl), with only a small sig-nal at about 2� = 6.1◦ which can be attributed to the clay. This signalhas decreased in intensity and a slight shift to smaller angles, indi-cating that the clay was intercalated by the polymer and almostcompletely exfoliated.

For all other nanocomposites synthesized with the differentclays similar results were obtained.

3.5. Transmission electron microscopy (TEM)

Fig. 4 shows the morphology of some nanocomposites obtainedby TEM. It is clearly possible to visualize the polymer around the

Ani-MMT 15A; (c) PAni-MMT 20A; (d) PAni-MMT 30B.

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Grande do Sul, 2008.[11] F.M. Smits, Bell System Technical Journal (1958) 710.

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amellae of clays. Almost all the clays were exfoliated, except theAni-MMT Na+ nanocomposite. This can be explained by the facthat MMT clays 10A, 15A, 20A and 30B are already organically

odified, which facilitates interaction with the aniline ion. TheMT-Na+ clay is the only one that does not have the ammonium

alt used as a modifier, difficulting the entrance of the monomeron between the layers of clay.

. Conclusions

The results demonstrated that it is possible to obtain PAni-MMTanocomposites by chemical synthesis method. The conductivitiesf the nanocomposites are lower than the PAni/HCl conductivityecause the clay is an insulating medium, but the nanocompositestill have an excellent electrical conductivity. The X-ray diffractionatterns and photomicrographs evidenced the efficient exfoliationf the clay by the PAni chains and the formation of PAni-MMTanocomposite.

cknowledgements

The authors would like to thank CAPES/PNPD and CNPq fornancial support.

[

Metals 183 (2013) 69– 72

References

[1] L.J. Lee, C. Zeng, X. Cao, X. Han, J. Shen, G. Xu, Composites Science and Technol-ogy 65 (15–16) (2005) 2344–2363.

[2] J.H. Koo, Polymer Nanocomposites: Processing, Characterization, and Applica-tions, McGraw-Hill, USA, 2006.

[3] L.A. Utracki, Clay-Containing Polymeric Nanocomposites, vol. 1, Rapra Tech-nology Limited, UK, 2004.

[4] J. Konta, Applied Clay Science 10 (4) (1995) 275–335.[5] R.A. Vaia, G. Price, P.N. Ruth, H.T. Nguyen, J. Lichtenhan, Applied Clay Science

15 (1–2) (1999) 67–92.[6] M. Biswas, S.S. Ray, Advances in Polymer Science 155 (2001)

167–221.[7] S.J. Park, D.I. Seo, J.R. Lee, Journal of Colloid and Interface Science 251 (1) (2002)

160–165.[8] K.S. Ho, K.H. Hsieh, S.K. Huang, T.H. Hsieh, Synthetic Metals 107 (1) (1999)

65–73.[9] L. Wen, N.M. Koncherginsky, Synthetic Metals 106 (1) (1999)

19–27.10] A.F. Baldissera, Development of non-conventional antifouling paint for ships

and protection of metallic structures, Doctoral thesis, Federal University of Rio

12] D. Aradilla, F. Estrany, D.S. Azambuja, M.T. Casas, J. Puiggali,C.A. Ferreira, C. Alemán, European Polymer Journal 46 (2010)977–983.