Polyaniline_carbon Nanotube Composites

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Pure Appl. Chem., Vol. 80, No. 11, pp. 2377–2395, 2008. doi:10.1351/pac200880112377 © 2008 IUPAC Polyaniline–carbon nanotube composites* Pandi Gajendran and Ramiah Saraswathi‡ Department of Materials Science, Madurai Kamaraj University, Madurai 625 021, Tamil Nadu, India Abstract: The key developments in polyaniline–carbon nanotube (PANI–CNT) composites are reviewed. Apart from in situ chemical polymerization and electrochemical deposition, a number of interesting approaches including the use o
  2377 Pure Appl.Chem. , Vol.80, No.11, pp.2377–2395, 2008.doi:10.1351/pac200880112377 ©2008 IUPAC Polyaniline–carbon nanotube composites* Pandi Gajendran and Ramiah Saraswathi ‡ Department of Materials Science, Madurai Kamaraj University, Madurai 625 021,Tamil Nadu, India   Abstract  : The key developments in polyaniline–carbon nanotube (PANI–CNT) compositesare reviewed. Apart from in situ chemical polymerization and electrochemical deposition, anumber of interesting approaches including the use of aniline functionalized CNTs and ultra-sound/microwave/  γ  -radiation initiated polymerization have been used in the preparation of composites. The structure and properties of these composites have been investigated by a va-riety of techniques including absorption, infrared (IR), Raman, X-ray photoelectron spec-troscopy methods, scanning electron and scanning probe microscopy techniques, cyclicvoltammetry, and thermogravimetry. The experimental results indicate favorable interactionbetween PANI and CNTs. The CNT content in these composites controls their conductive,mechanical, and thermal properties. The most interesting characteristic is their easy dis-persibilityin aqueous solution. The performance evaluation studies of PANI–CNT compos-ites in a number of applications including supercapacitors, fuel cells, sensors, and actuatorsare highlighted. Keywords : polyaniline; conducting polymers; carbon nanotubes; composites; electroactivepolymers. INTRODUCTION Electroactive polymers have been an area of immense interest over the past 30 years since the first dis-covery of conducting polyacetylene in 1977 by Shirakawa et al. [1]. Extensive research on several con- jugated polymers including poly(  p -phenylene), polyaniline (PANI), polypyrrole, polythiophene, poly-indole, polycarbazole, polyfluorene, poly(  p -phenylenevinylene), and their substituted derivatives haveled to their applications in rechargeable batteries, microelectronics, sensors, electrochromic displays,and light-emitting and photovoltaic devices [2,3]. Among the various conjugated polymers, PANI(Scheme1) has received special recognition owing to its good stability and interesting redox behavior[4–9]. In the past few years, several novel methodologies have been developed for the preparation of nanostructured PANI in the form of dispersions, nanowires, nanofibers, and nanotubules [10–16]. *Paper based on a presentation at the 3 rd International Symposium on Novel Materials and Their Synthesis (NMS-III) and the17 th International Symposium on Fine Chemistry and Functional Polymers (FCFP-XVII), 17–21 October 2007, Shanghai, China.Other presentations are published in this issue, pp. 2231–2563. ‡ Corresponding author  The discovery of fullerenes [17] and carbon nanotubes (CNTs) [18] has led to an explosion of re-search in nanoscience and nanotechnology. In fact, the focus in nanoscience has since shifted from syn-thesis to applications. A logical extension is to find new combinations of the existing materials as hy-brid materials, blends, and nanocomposites for exploitation of their complementary properties [19–22].In this context, there has been a new surge of interest in developing conducting polymer–CNT com-posites as novel futuristic materials. One main reason for this is that common applications of the twocomponents offer the possibility to observe synergetic effects. Already, various studies have proved thatcertain discrete properties of the components of conjugated polymer–CNT composites are enhanced,thus validating their high suitability for some technological applications [23,24].This review focuses mainly on the extensive literature published since 1999, on the preparation,characterization, and applications of PANI–CNT nanocomposites. The possible interactions betweenPANI and CNT that may be responsible for enhancement in certain properties of the composites arehighlighted. Wherever applicable, the literature on CNT composite materials with substituted deriva-tives of PANI is also included. PREPARATIVE METHODS Since the first report in 1999 on the efficient electropolymerization of aniline on CNT whiskers [25], anumber of innovative methodologies have been developed for preparing PANI–CNT composites. Ageneral scheme of the common preparative methods is given (Scheme2).Apart from direct solid-state mixing [26] and dispersal of CNTs in PANI solutions of   N  -methyl-2-pyrrolidinone [27] or HCl [28], several chemical and electrochemical procedures have been re-ported. A simple method is in situ chemical polymerization of aniline in an acidic dispersion of multi-wall carbon nanotubes (MWCNTs) or single-wall carbon nanotubes (SWCNTs) in the presence of anoxidant at low temperature [29,30]. The in situ chemical polymerization has been used also in thepreparation of composites of substituted PANI like poly( o -anisidine) [31], poly(  N  -methylaniline) [32],poly(diphenylamine) [33], and poly( o -aminobenzoic acid) [34] with either SWCNTs or MWCNTs. P.GAJENDRAN AND R.SARASWATHI ©2008 IUPAC, Pure and Applied Chemistry  80, 2377–23952378 Scheme 1 ES and EB forms of PANI.   ©2008 IUPAC, Pure and Applied Chemistry  80, 2377–2395 Polyaniline–carbon nanotube composites  2379 Scheme 2 Generalized scheme of preparative methods of PANI–CNT composites.  Chemical functionalization of MWCNTs with an acyl chloride group has been used to increasethe interfacial binding between CNTs and PANI [35]. In a similar way, a nanotubular composite hasbeen prepared using  p -phenylenediamine functionalized MWCNT [36,37]. A sulfonated MWCNT canbe used as the self-assembled template in the formation of PANI nanostructures [38]. A water-solubleself-doped PANI–SWCNT composite has been obtained by in situ polymerization of 3-aminophenyl-boronic acid monomer in the presence of DNA-functionalized SWCNT [39]. Nanocables of PANI–CNT composites can be obtained by the chemical oxidative polymerization of aniline from aque-ous dispersions of CNT containing a sufficiently high concentration of a cationic surfactant likecetyltrimethylammonium bromide or a non-ionic surfactant like poly(ethylene glycol)mono-  p -nonylphenyl ether [40,41]. In situchemical polymerization in an aqueous emulsion mixture containing asmall quantity of dimethylbenzene has been carried out in the presence of CNT and sodium dodecyl-benzene sulfonate [42]. The use of poly(vinyl alcohol) as stabilizer in the composite preparation hasbeen reported [43]. An in situ inverse microemulsion route using sodium dodecylbenzene sulfonate hasresulted in the formation of a core-shell PANI–MWCNT nanocomposite (Scheme3) [44]. An opticallyactive PANI–CNT composite has been prepared by in situ polymerization in the presence of ( S  )-(+)-10-camphorsulfonic acid [45–47]. A post-sulfonation procedure with chlorosulfonic acid in1,2-dichloroethane has been adopted to prepare a water-soluble composite [48]. The effects of ultra-sound, microwave, and γ  -radiations on the formation of PANI–CNT composites have been explored[49–52]. P.GAJENDRAN AND R.SARASWATHI ©2008 IUPAC, Pure and Applied Chemistry  80, 2377–23952380 Scheme 3 Preparation of PANI–CNT core-shell nanocomposite by inverse microemulsion route (reproduced fromref. [44]).
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