Preparation and Characterization of Clay (Maghnite-H)/Poly(3,4-Ethylenedioxythiophene) Composites

Affaf Megherbi, Rachid Meghabar, Mohammed Belbachir

Laboratory of Polymers Chemistry, Department of Chemistry, Faculty of Sciences, University of Oran, Oran, Algeria.

DOI: 10.4236/jsemat.2013.31004                

Abstract

Composites of Maghnite-H, a Montmorillonite sheet silicate clay, exchanged with protons, and Poly(3,4-ethylenedioxythiophene) (PEDOT) were prepared by in situ chemical polymerization of the 3,4-ethylenedioxythiophene, without the use of solvent or oxidant. The effect of changing monomer/clay ratio was studied and the resultant composite structures were characterized by Inferred spectroscopy, ²⁷Al and ¹³CSolid-State NMR spectroscopy, scanning electron microscopy and powder X-ray diffraction. All analyses are consistent with a structure were the polymer is (partially) intercalated into the clay structure, which in favourable cases lead to exfoliation. The presence of the clay in the polymer leads to a desired increase in thermal stability as witnessed by thermogravimetry.

Keywords

Poly(3, 4-Ethylenedioxythiophene); PEDOT; Clay; Maghnite-H; Montmorillonite

1. Introduction

Polythiophene and its derivatives have attracted much interest over recent decades due to exceptional electrical properties and their environmental stability [1-6]. From this class of conducting polymers with conjugated π- bonds, especially poly 3,4-ethylenedioxythiophene (PEDOT) possess unique properties such as high environmental stability [7,8] and a small band gab (1.6 - 1.7 eV); a direct consequence of the electron donation properties of the ether functionality [9]. In addition, the electronic conductivity can reach as high as 300 S/cm after the polymer has been oxidized [10]. These characteristics have lead to several applications, such as antistatic paints [11,12], electrochromic devices [13,14], electrochemical capacitors [15], biosensors [16-18], polymer solar cells (PSCs) [19,20], polymer light-emitting diodes (PLEDs) [21,22] etc. Polymerisation of EDOT may be accomplished by either electrochemical or chemical oxidation. Both techniques lead to a material which is in his native state is insoluble and cannot be melted below the decomposition temperature [6,23]. This problem has been resolved by researchers at Bayer AG., Germany, by persulfate oxidative polymerization in a solution containing a polyelectrolyte (polystyrene sulfonic acid) [24]. More recently, aqueous solvated nanoparticles of PEDOT have been prepared using ammonium perdisulfate and the surfactant dodecylbenzene [25]. Another approach to polymer structures with nanometer dimensions is to form clay/polymer hybrids. These hybrids have found numerous applications due to their mechanical properties, their thermal stability and their reduced permeability to gases [26]. Recent examples include hybrids of clay and polyaniline [27,28], and clay and polypyrrole [29]. An especially elegant approach to these composites is the solvent-free direct reaction between the clay and the monomer, where the clay serves the double role of reactant/ catalyst for the polymerization and inorganic component of the final hybrid material. In this manner Biswas et al. [30,31] have prepared composites of Poly(N-vinylcarbazole) and polypyrrole by direct reaction with montmorillonite. Sadok et al. [32] have prepared polypyrrole composites by using a clay montmorillonite naturally rich in ions or synthetically doped with ions (Saponite substituted with Fe³⁺ in tetrahedral sites). Surprising little clay composite studies have been performed on polymers which contain the thiophene functionality. A notable exception is Ballav et al. [33] who have succeeded in preparing composites polythiophene/montmorillonite, by solvent-free direct reaction between the monomer and montmorillonite-Na⁺. The composites produced showed that the polythiophene was intercalated in the interlayer space and that the resultant material showed a modest but non-zero electronic conductivity on the order of 10⁻⁴ S/cm.

In this article, we examine the use of Maghnite-H⁺ (MagH), a Montmorillonite sheet silicate, in the synthesis of composites with PEDOT. The choice of MagH is based on related work where it acts as a catalyst of cationic polymerization of vinyl [34-37] and heterocylic [38-42] monomers. Here the synthesis takes place in a one pot reaction between the clay and the monomer without the use of solvent or oxidant. Specifically, we examine the effect of the relative ratios between the monomer and the clay on the intercalation and possible exfoliation of the clay structure.

2. Experimental

2.1. Materials

MagH was prepared using the method of Belbachir et al. [34]. EDOT was obtained from Bayer AG. (Leverkusen, Germany) and used without further purification.

2.2. Synthesis

All reactions were performed using the same methodology described below, with however, a variation of time, for the 10% by weight of MagH/monomer 24 h reaction and for 50% 96 h reaction. The reaction times and relative concentration were altered according to Table 1.

Hybrides from 10% by weight of MagH/monomer reaction mixtures.

In a round bottom flask fitted with a condenser was mixed 1 g (0.007 mol) EDOT and 0.5 g MagH previously dried at 100˚C overnight. The mixture was heated to 90˚C, under constant stirring using a magnetic stir bar. Upon the addition of the MagH a colour change was witnessed from clear over red to brown before finally becoming dark green. After 24 h of heating a back solid was formed, and the suspension was cooled to room temperature. Residual unreacted monomer and shorter solvable oligomeres were removed by washing with dichloromethane. The residual black solid (the hybrid material) was dried at 60˚C overnight to remove any solvent traces. (Calculate a real yield based on incorporated polymer relative to the initial amount). The amount of incorporated polymer was determined to 21 m/m-% based on the mass gain.

2.3. Characterization

Infrared spectra (400 - 4000 cm⁻¹) were collected from samples ground with dry KBr and pressed into pellets. Spectral peaks around 2350 cm⁻¹ stem from residual CO² in the beam path. ¹³C and ²⁷Al Solid state NMR was preformed using a BRUKER ASX 400 CP-MAS. Thermogravometric analysis (TGA) was performed on a Standon Redcroft STA780 thermal analyser and in air at a heating rate of 5 deg/min within the temperature range of 25˚C - 1000˚C. The powder X-ray diffraction (XRD) patterns of the samples were recorded using Philips XRD X’PERT PRO II diffractometer (2 goniometers, Montpellier, French) using Cu-Kα radiation and (λ = 1.5404 Å) produced at 40 kV and 40 mA. Scanning electron microscopy micrographs where collected on a Hitachi S-2600N with a 25 kV working potential, a working distance of 7.0 - 7.4 mm and a SE detector.

3. Results and Discussion

3.1. Characterization by Infrared Spectra (IR)

Figure 1 shows, respectively, the spectra IR of MagH, the composites MagH-PEDOT (1): B and MagH-PEDOT (2): C and of polymer PEDOT: D Vibrations around 1337 and 1518 cm⁻¹. (B, C, D) are due respectively to the elongation of C-C and C=C bonds of the thiophene cycle, these peaks do not appear in the IR spectrum of MagH. Peaks located at 980, 833 and 794 cm⁻¹ are due to the vibrations of the CS bond in thiophene, and signals around 1080 cm⁻¹ indicate C-O-C bond of the ethylenedioxy group. The weak peaks from 2854 to 2925 cm⁻¹ show the CH elongations of ethylene related to the thiophene cycle. All IR peaks found in the composites, compared with the peaks of MagH and PEDOT, confirm the presence of PEDOT in the composites. Kvarnstrom and et al. [9] and Jeong et al. [25] have obtained same results in the synthesis of the PEDOT.

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	N. Hari-Singh, “Handbook of Organic Conductive Molecules and Polymers,” John Wiley & Sons Ltd., New York, 1997.
[2]	G. Tourrillan, “Polythiophene and Its Derivatives,” In: T. A. Skotheim, Ed., Handbook of Conducting Polymers, Marcel Dekker, New York, 1986, p. 293.
[3]	A. Kossmehl, “Semi-Conducting and Conducting Polymers with Aromatic and Heteroaromatic Units,” In: T. A. Skotheim, Ed., Handbook of Conducting Polymers, Marcel Dekker, New York, 1986, p. 351.
[4]	G. Schopf and G. Kossmehl, “Polythiophenes—Electrically Conducting Polymers,” Springer-Verlag, Berlin, 1997.
[5]	D. Kumar and R. C. Sharma, “Advances in Conductive Polymers,” European Polymer Journal, Vol. 34, No. 8, 1998, pp. 1053-1060. doi:10.1016/S0014-3057(97)00204-8
[6]	L. Groenendaal, F. Jonas, D. Freitag, H. Pielartzik and J. R. Reynolds, “Poly(3,4-Ethylenedioxythiophene) and Its Derivatives: Past, Present, and Future,” Advanced Materials, Vol. 12, No. 7, 2000, pp. 481-494. doi:10.1002/(SICI)1521-4095(200004)12:7<481::AID-ADMA481>3.0.CO;2-C
[7]	H. Yamato, M. Ohwa and W. Wernet, “Stability of Polypyrrole and Poly(3,4-Ethylenedioxythiophene) for Biosensor Application,” Journal of Electroanalytical Chemistry, Vol. 397, No. 1-2, 1995, pp.163-170.
[8]	I. Winter, C. Reese, J. Hormes, G. Heywang and F. Jonas, “The Thermal Ageing of Poly(3,4-Ethylenedioxythiophene). An Investigation by X-Ray Absorption and X-Ray Photoelectron Spectroscopy,” Chemical Physics, Vol. 194, No. 1, 1995, pp. 207-213. doi:10.1016/0301-0104(95)00026-K
[9]	C. Kvarnstrom, H. Neugebauer, S. Blomquiste, H. J. Ahomen, J. Kankare and A. Ivaska, “In Situ Spectro-Electrochemical Characterization of Poly (3, 4-Ethylene-dioxythiophene),” Electrochimica Acta, Vol. 44, No. 16, 1999, pp. 2739-2750. doi:10.1016/S0013-4686(98)00405-8
[10]	A. N. Aleshin, R. Hiebooms and A. J. Heeger, “Metallic Conductivity of Highly Doped Poly(3,4-Ethylenedioxy-thiophene),” Synthetic Metals, Vol. 101, No. 1-3, 1999, pp. 369-370. doi:10.1016/S0379-6779(98)00758-9
[11]	F. Jonas and L. Schrader, “Conductive Modifications of Polymers with Poly-Pyrroles and Polythiophenes,” Synthetic Metals, Vol. 41, No. 3, 1991, pp. 831-836.
[12]	F. Jonas and J. T. Morrisson, “3,4-Polyethylenedioxy Thiophene (PEDT): Conductive Coat-ings Technical Applications and Properties,” Synthetic Metals, Vol. 85, No. 1-3, 1997, pp. 1397-1398.
[13]	Q. Pei, G. Zucarello, M. Ahlskog and O. Ingan?s, “Electrochromic and Highly Stable Poly(3,4-Ethylenedioxy-thiophene) Switches between Opaque Blue-Black and Transparent Sky Blue,” Polymer, Vol. 35, No. 7, 1994, pp. 1347-1351. doi:10.1016/0032-3861(94)90332-8
[14]	A. Kumar, D. M. Welsh, M. C. Morvant, F. Piroux, K. A. Abboud and J. R. Reynolds, “Conducting Poly(3,4-Alky-lenedioxythiophene) Derivatives as Fast Electrochromics with High-Contrast Ratios,” Chemistry of Materials, Vol. 10, No. 3, 1998, pp. 896-902. doi:10.1021/cm9706614
[15]	J. C. Carlberg and O. Ingan?s, “Poly(3,4-Ethylenedioxy-thiophene) as Electrode Material in Electrochemical Capacitors,” Journal of the Electrochemical Society, Vol. 144, No. 4, 1997, L61-L64. doi:10.1149/1.1837553
[16]	N. Rozlosnik, “New Directions in Medical Biosensors Employing Poly(3,4-Ethylenedioxy Thiophene) Derivative-Based Electrodes,” Analytical and Bioanalytical Chemistry, Vol. 395, No. 3, 2009, pp. 637-645. doi:10.1007/s00216-009-2981-8
[17]	R. D. McCullough, P. C. Ewbank and R. S. Loewe, “Self-Assembly and Disassembly of Regioregular, Water Soluble Polythiophenes: Chemoselective Ionchromatic Sensing in Water,” Journal of the American Chemical Society, Vol. 119, No. 3, 1997, pp. 633-634. doi:10.1021/ja963713j
[18]	F. Le Floch, H. A. Ho, P. Harding-Lepage, M. Bedard, R. Neagu-Plesu and M. Leclerc, “Ferrocene-Functionalized Cationic Polythiophene for the Label-Free Electrochemical Detection of DNA,” Advanced Materials, Vol. 17, No. 10, 2005, pp. 1251-1254. doi:10.1002/adma.200401474
[19]	C. J. Brabec, N. S. Sariciftci and J. C. Hummelen, “Plastic Solar Cells,” Advanced Functional Materials, Vol. 11, No. 1, 2001, pp. 15-26. doi:10.1002/1616-3028(200102)11:1<15::AID-ADFM15>3.0.CO;2-A
[20]	K. M. Coakley and M. D. McGehee, “Conjugated Polymer Photovoltaic Cells,” Chemistry of Materials, Vol. 16, No. 23, 2004, pp. 4533-4542. doi:10.1021/cm049654n
[21]	L. Akcelrud, “Electroluminescent Polymers,” Progress in Polymer Science, Vol. 28, No. 6, 2003, pp. 875-962. doi:10.1016/S0079-6700(02)00140-5
[22]	I. F. Perepichka, D. F. Perepichka, H. Meng and F. Wudl, “Light-Emitting Polythiophenes,” Advanced Materials, Vol. 17, No. 19, 2005, pp. 2281-2305. doi:10.1002/adma.200500461
[23]	F. Jonas, W. Krafft and B. Muys, “Poly(3, 4-Ethylene-dioxythiophene): Conductive Coatings, Technical Applications and Properties,” Macromolecular Symposia, Vol. 100, No. 1, 1995, pp. 169-173. doi:10.1002/masy.19951000128
[24]	B. Sankaran and J. R. Reynolds, “High-Contrast Electrochromic Polymers from Alkyl-Derivatized Poly(3,4-Ethylenedioxy Thiophenes),” Macromolecules, Vol. 30, No. 9, 1997, pp. 2582-2588. doi:10.1021/ma961607w
[25]	W. C. Jeong, G. H. Moon, Y. Sook, G. O. Seong and S. I. Seung, “Poly(3,4-Ethylenedioxythiophene) Nanoparticles Prepared in Aqueous DBSA Solutions,” Synthetic Metals, Vol. 141, No. 3, 2004, pp. 293-299.
[26]	S. K. Lim, J. W. Kim, I. Chim, Y. K. Kwon and H. J. Choi, “Preparation and Interaction Characteristics of Organically Modified Montmorillonite Nanocomposite with Miscible Polymer Blend of Poly(Ethylene Oxide) and Poly(Methyl Methacrylate),” Chemistry of Materials, Vol. 14, No. 5, 2002, pp. 1989-1994. doi:10.1021/cm010498j
[27]	N. Boutaleb, A. Benyoucef, H-J. Salavagione, M. Belbachir and E. Morallón, “Electrochemical Behaviour of Conducting Polymers Obtained into Clay-Catalyst Layers. An in Situ Raman Spectroscopy Study,” European Polymer Journal, Vol. 42, No. 4, 2006, pp. 733-739. doi:10.1016/j.eurpolymj.2005.10.012
[28]	J. W. Kim, S. G. Kim, H. J. Choi, M. S. Suh, M. J. Shin and M. J. Jhon, “Synthesis and Electrorheological Characterization of Polyaniline and Na+-Montmorillonite Clay Nanocomposite,” International Journal of Modern Physics B, Vol. 15, No. 06n07, 2001, pp. 657-664.
[29]	J.W. Kim, F. Liw, H. J. Choi, S. H. Hong and J. Joo, “Intercalated Polypyrrole/Na+-Montmorillonite Nano-Composite via an Inverted Emulsion Pathway Method,” Polymer, Vol. 44, No. 1, 2003, pp. 289-293. doi:10.1016/S0032-3861(02)00749-8
[30]	M. Biswas and S. S. Ray, “Preparation and Evaluation of Composites from Mont-morillonite and Some Heterocyclic Polymers. 1: Poly(N-Vinylcarbazole)-Montmorillonite Nanocomposite System,” Polymer, Vol. 39, No. 25, 1998, pp. 6423-6428. doi:10.1016/S0032-3861(97)10366-4
[31]	S. S. Ray and M. Biswas, “Preparation and Evaluation of Composites from Montmorillonite and Some Heterocyclic Polymers: 3. a Water Dispersible Nanocomposite from Pyrrole-Montmorillonite Polymerization System,” Materials Research Bulletin, Vol. 34, No. 8, 1999, pp. 1187-1194.
[32]	L. Sadok, A. Pilar and R. H. Eduardo, “Influence of Iron in the Formation of Conductive Polypyrrole-Clay Nanocomposites,” Applied Clay Science, Vol. 28, No. 1-4, 2005, pp. 183-198.
[33]	N. Ballav and M. Biswas, “A Conducting Nanocomposite via Intercalative Polymerisation of Thiophene in Montmorillonite Clay,” Synthetic Metals, Vol. 142, No. 1-3, 2004, pp. 309-315. doi:10.1016/j.synthmet.2003.08.004
[34]	M. Belbachir and A. Bensaoula, “Composition and Method for Catalysis Using Bentonites,” US Patent: 7,094,823, 2006.
[35]	A. Harrane, R. Meghabar and M. Belbachir, “A Protons Exchanged Montmo-rillonite Clay as an Efficient Catalyst for the Reaction of Iso-butylene Polymerization,” International Journal of Molecular Science, Vol. 3, No. 7, 2002, pp. 790-800. doi:10.3390/i3070790
[36]	R. Meghabar, A. Megherbi and M. Belbachir, “Maghnite-H+, an Ecocatalyst for Cationic Polyme-rization of N-Vinyl- 2-Pyrrolidone,” Polymer, Vol. 44, No. 15, 2003, pp. 4097-4100. doi:10.1016/S0032-3861(03)00400-2
[37]	M. Chabani, A. Yahiaoui, A. Hachemaoui and M. Belbachir, “New Approach for the Polymerization of 2-Chloroethyl Vinyl Ether Using a Maghnite Clay as Eco-Catalyst,” Journal of Applied Polymer Science, Vol. 122, No. 3, 2011, pp. 1800-1806. doi:10.1002/app.34242
[38]	A.Yahioui, M. Belbachir and A. Hachmaoui, “An Acid Exchanged Montmorillonite Clay-Catalyzed Synthesis of Polyepichlorhydrin,” International Journal of Molecular Science, Vol. 4, No. 10, 2003, pp. 548-561. doi:10.3390/i4100548
[39]	A. Harrane, K. Oussadi, M. E. Belaoudj, R. Meghabar and M. Belbachir, “Cationic Ring Opening Polymerization of Glycolide Catalysed by a Mont-morillonite Clay Catalyst,” Journal of Polymer Research, Vol. 12, No. 5, 2005, pp. 361-365.
[40]	A. Harrane, R. Meghabar and M. Belbachir, “Polymerization of Epsilon-Caprolactone Using a Montmorillonite Clay as Catalyst,” Designed Monomers and Polymers, Vol. 8, No. 1, 2005, pp. 11-24. doi:10.1163/1568555053084203
[41]	A. Harrane, R. Meghabar and M. Belbachir, “In Situ Polymerization of -Caprolactone Catalysed by Maghnite-TOA to Produce Poly(-Caprolactone)/Montmorillonite Nanocomposites,” Designed Monomers and Polymers, Vol. 9, No. 2, 2006, pp. 181-191. doi:10.1163/156855506776382673
[42]	K. Oussadi, V. Montembault, M. Belbachir and L. Fontaine, “Ring-Opening Bulk Polymerization of Five- and Six-Membered Cyclic Phosphonates Using Maghnite, a Nontoxic Proton Exchanged Montmorillonite Clay,” Journal of Applied Polymer Science, Vol. 122, No. 2, 2011, pp. 891-897. doi:10.1002/app.34193
[43]	H. Meng, D. F. Perpichka and F. Wudl, “Facile Solid-State Synthesis of Highly Conducting Poly(Ethylenedi-oxythiophene),” Angewandte Chemie International Edition, Vol. 42, No. 6, 2003, pp. 658-661. doi:10.1002/anie.200390181