Composite polymers, polyaniline

Conducting polymers, polyaniline, catalytic activity, PANI/expanded graphite composites, metal-air batteries, primary rechargeable cells. 

In addition to catalysis of small molecule transformations and biocatalysis, non-functionalized LLC phases used as reaction media have also been found to accelerate polymerization reactions as well. For example, the L and Hi phases of the sodium dodecylsulfate/n-pentanol/sulfuric acid system have been found to lower the electric potential needed to electropolymerize aniline to form the conducting polymer, polyaniline [110]. In this system, it was also found that the catalytic efficiency of the L phase was superior to that of the Hi phase. In addition to this work, the Ii, Hi, Qi, and L phases of non-charged Brij surfactants (i.e., oligo(ethylene oxide)-alkyl ether surfactants) have been observed to accelerate the rate of photo-initiated radical polymerization of acrylate monomers dissolved in the hydrophobic domains [111, 112]. The extent of polymerization rate acceleration was found to depend on the geometry of the LLC phase in these systems. Collectively, this body of work on catalysis with non-functionalized LLC phases indicates that LLC phase geometry and system composition have a large influence on reaction rate. 

A. Yoshizawa, M. Takeda, Y. Oura, Y. Takemoto and K. Naoi, Low-molecular-weight soluble polyaniline for electrolytic capacitor, Electrochemistry, 1999, 67, 45 H. Yamamoto, K. Kanemoto, M. Oshima and I. Isa, Self-healing characteristics of solid electrolytic capacitor with polypyrrole electrolyte, Electrochemistry, 1999, 67, 855 M. Mastragostino, R. Paraventi and A. Zanelli, Supercapacitors based on composite polymer electrodes, J. Electrochem. Soc., 2000,147, 3167. 

Scheme 29.3 Generalized composition of polyanilines indicating the (a) reduced and oxidized units, (b) completely reduced polymers, (c) half-oxidized polymer, and (d) fully oxidized polymer.

J. Jang, J. Bae, and K. Lee, Synthesis and characterization of polyaniline nanorods as curing agent and nanofiUer for epoxy matrix composite. Polymer, 46, 3677-3684 (2005). 

C. Su, G. Wang, F. Huang, and X. Li, Melt-processed polyaniline nanofibers/LDPE/EAA conducting composites, Polym. Compos., 29, 1177-1182 (2008). 

M. Deka, A. K. Nath, and A. Kumar, Effect of dedoped (insulating) polyaniline nanofibers on the ionic transport and interfacial stability of poly(vinylidene fluoride-hexafluoropropylene) based composite polymer electrolyte membranes, J. Membrane Set, ill, 188-194 (2009). 

G. Neelgund, E. Hrehorova, M. Joyce, and V. Bbznyuk, Synthesis and characterization of polyaniline derivative and silver nanoparticle composites, Polym. Int., 57, 1083 1089 (2008). 

The solubility of this conducting polymer opens the way to processing pure, partially crystalline polyanilin or composites of polyanilin with the other commercial polymers into fibers and films, etc. In addition, this solubility enables extensive characterization of polyaniline as a macromolecular system (e.g. viscosity in solution as a probe of molecular weight, etc.) and of polyaniline as a conducting polymer (e.g. optical studies of spin-cast films as a probe of electronic structure of the salt or base forms). The latter is the subject of this paper. 

Rakhi et al reported the conducting-polymers (polyaniline [PANI] and PPy)-coated carbon nanocoils (CNCs) as efficient binder-free electrode materials for supercapacitors for the first time, in which the CNCs acted as a perfect backbone for the uniform distribution of the conducting polymers in the composites [16]. Ihe SC and maximum storage energy per unit mass of the composites were found to be comparable to one of the best-reported values for polymer-coated MWNTs. Dumanli et al. prepared the chemically bonded carbon nanofibers (CNFs)-PPy composite via electro-polymerization of Py on CNFs [17]. It showed that the final capacitance values were highly dependent on the number of deposition cycles and deposition rates. The best result for the coiled CNF-PPy composite system was found to be 27.6 C/cm at six times cycling using 25 mV/s. 

Fibers containing intrinsically conductive polymer are manufactured from a composition containing an organic acid salt of an intrinsically conductive polymer, a matrix polymer, and a spinning solvent. Polyaniline is the intrinsically conductive polymer. Polyaniline alone cannot be processed into fiber because of its low solubility (standard wet spinning methods require a polymer concentration of 15-20%). Many polymers can be used as the matrix polymer. For this application, polyacrylonitrile was selected. A variety of solvents can be used but dimethylacetamide was found to be the most useful. 

When the first method is used, the PB film is deposited directly on the conducting polymer film, with the polymer acting as an extended electrode. Composites of polyaniline and PB switch from pale yellow when reduced to hlue when oxidized, the combination of the colors exhibited by the host materials [237,238]. When PB is combined with polypyrrole in a composite film, the absorbance of the film is extended to a wider region of the visible spectrum compared with the pure polypyrrole. These films switch from pale brown in the reduced state to bluish green in the oxidized state [238—240]. 

Barthet, C., et al. 1997. A polyaniline - - polyethylene oxide mixture as a composite polymer positive electrode in solid-state secondary batteries. J Electroanal Chem 431 145. 

Tiitu, M., et al. 2005. Aminic epoxy resin hardeners as reactive solvents for conjugated polymers Polyaniline base/epoxy composites for anticorrosion coatings. Polymer 46 (18) 6855. 

Mirmohseni, A., and G.G. Wallace. 2003. Preparation and characterization of processahle electroactive polyaniline-polyvinyl alcohol composite. Polymer 44 (12) 3523. 

J. Alam, U. Riaz and S. Ahmad, Nanostructured polyaniline reinforced sustainable resource (soy oil alkyd) based composites , Polym Compos, 2010, 31, 32-7. 

Carbon-coated LiFePO (C-LFP) composites incorporated with electro-chemically active conducting polymer polyaniline (PANI) were fabricated in situ by chemical oxidative polymerization as cathode for LIB. Specific capacities as high as 165 mAh/g at 0.2 C, 133 mAh/g at 7 C and 123 mAh/g at 10 C were observed in C-LFP/7 wt% PANI composite. The improved cyclability as compared with the parent C-LFP was due to PANI, which acts not only as an additional host for Li -ion insertion/extraction, but also as a binder to modify the electrode surface and a container for electrolyte to penetrate into C-LFP particles [55]. 

Polyaniline has only recently been employed to support Pt particles for oxygen reduction (10,11). In one approach, polyaniline films were cast onto glassy carbon electrodes fi om a solution of camphorsulfonic acid doped polyaniline, and then Pt was electrochemically deposited firom a H2PtCl5 solution. The pol iline film was found to provide a higher surfoce area for Pt deposition but exhibited limited permeability to oxygen. Use of a composite of polyaniline and Nafion (a proton conducting polymer commonly used in the fabrication of fiiel cell electrodes) resulted in better oxygen permeabilty (11). 

Electrical properties have been reported on numerous carbon fiber-reinforced polymers, including carbon nanoflber-modified thermotropic liquid crystalline polymers [53], low-density polyethylene [54], ethylene vinyl acetate [55], wire coating varnishes [56], polydimethyl siloxane polypyrrole composites [50], polyacrylonitrile [59], polycarbonate [58], polyacrylonitrile-polycarbonate composites [58], modified chrome polymers [59], lithium trifluoromethane sulfonamide-doped polystyrene-block copolymer [60], boron-containing polyvinyl alcohols [71], lanthanum tetrafluoride complexed ethylene oxide [151, 72, 73], polycarbonate-acrylonitrile diene [44], polyethylene deoxythiophe-nel, blends of polystyrene sulfonate, polyvinyl chloride and polyethylene oxide [43], poly-pyrrole [61], polypyrrole-polypropylene-montmorillonite composites [62], polydimethyl siloxane-polypyrrole composites [63], polyaniline [46], epoxy resin-polyaniline dodecyl benzene sulfonic acid blends [64], and polyaniline-polyamide 6 composites [49]. 

Bacterial cellulose has been used as a material in combination with many others to develop composites. It has been used with materials such as xmsaturated polyester [185], the conducting polymer polyaniline [158-162, 186], as well as various acrylic and phenolic resins [178, 187-189]. It has also been used with several biodegradable materials such as cellulose acetate butyrate (CAB) [146,190], PLA [167,174,191,192], PHB [193-195], PVA [196,197], and thermoplastic starch [198,199], to produce completely biodegradable composites. Though renewable and biodegradable composites are the focus of this review, techniques and resulting composites from non-renewable sources are also mentioned. 

Conductivity of the anode is important to MF C performance. One method that has been suecess-fully used to increase conductivity and current densities of MFC is the application of the eonductive polymer polyaniline (Schroder etal., 2003). However, performance was only improved temporarily as polyaniline was shown to be unstable and susceptible to microbial degradation (Niessen et al., 2004). While these findings would seemingly limit polyaniline s potential contribution to future MFC designs research has suggested that it may be possible to improve both the stability and performance of polyaniline by making composites combined with fluorine, carbon nanotubes (Qiao et al., 2007) and titanium dioxide (Qiao et al., 2008). 

Enhanced performance was also reported for anode modification with conductive polymers. A commonly used conductive polymer, polyaniline, can increase the current densities of MFC anodes. But it is also susceptible to microbial attack and degradation [39]. Schroder et al. [18] reported that a platinum electrode covered with polyaniline achieved a current density up to l.SmAcm in an MFC. Modification of polyaniline can improve its performance and stability, such as fluorinated PANI [40], PANI/carbon nanotube (CNT) composite [41], and PANI/titanium dioxide composite [42]. 

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