Nanowires PANi

As revealed by FTIR and UV-Vis spectra in other studies, all PANI nanotubes, nanofibers, nanowires, nanorods, as well as microtubes, have backbone structures similar to that of the conventionally prepared granular PANI. In some cases, the Einstein shifts observed in the FTIR and UV-Vis spectra were ascribed to the interaction between the PANI chains and some small molecules, such as ethanol rather than to the chemical structures. 

PANI Films and Nanowires Prepared with Enzymatically Synthesized PANI 1199... 

One of the major drawbacks of PANI is its processability, which is not as good as that of thermoplastics. Unfortunately, many of the PANI applications require its use either as thin film, free-standing film, fiber or nanowires. Several methods to prepare films, which were first studied with chemically synthesized PANI, such as in situ chemical deposition, casting using solvents, and layer by layer assemblies, have been adapted in order to process PANI using the enzymatically synthesized polymer. 

PANI nanowires are ID nanostructures which are very interesting from the nanotechnology point of view, due to their potential use in sensors and nanoscale electronic devices. DNA can be considered as an anionic polyelectrolyte that can behave as a template for PANI enzymatic polymerization in solution [20]. Double stranded DNA can be attached to aminated surfaces by electrostatic self assembly, providing a linear template for further aniline electrostatic assembly. By using this method followed by enzymatic polymerization of the assembled aniline, Ma et al. [69] and Nickels et al. [70] showed that stretched DNA molecules were able to template the enzymatic synthesis of PANI nanowires, according to the mechanism showed in Figure 8.7. 

Figure 8.7 Enzymatic synthesis of PANI nanowires attached to silicon surface (Reproduced with permission from[69]. Copyright (2004) American Chemical Society).

Studies performed by Yuan et al. on conductive polyaniline (PANI) nanofibers, P3DOT, and CNT thin films show that aU three are capable of forming highly compliant electrodes with fault tolerant behavior [225]. Nanowires and tubes are of particular interest since they are capable of maintaining a percolation network at large strains, thus reducing the required electrode thickness while still allowing for maximum strain performance. 

Figure 2.15 The highly oriented conducting PANI-NFs formed in the complexes of the PAN emeraldine base with a phosphoric acid-terminated PEO (from Table of Contents of Reference 302). (Reprinted with permission from Macromolecules, Highly Oriented Nanowires from the Hierarchical Self-Assembly in Supramolecular Complex of Polyaniline with Lu-Methoxypoly(ethylene oxide) Phosphates by B. Nandan,J.-Y. Hsu, A. Chiba etai, 40,3, 395-398. Copyright (2007) American Chemical Society)...

Au/PANI-CSA coaxial nanocables have been successfully synthesized by the oxidation of aniline with chloroauric acid in the presence of CSA [397]. PANI-CSA nanotubes were obtained by dissolving the Au nanowire core of the Au/PANI-CSA nanocables. Purified flagella fibers displaying an anionic aspartate-glutamate loop peptide with 18 carboxylate groups were used to initiate formation of PANI-NTs [398]. 

Figure 2.32 Field-effect transistor based on single conducting PANI-NF. (Reprinted with permission from Journal of Physical Chemistry C, Field-Effect Transistors based on Single NanowIres of Conducting Polymers by A. K. Wanekaya, Mangesh A. Bangat et al., 111, 13, 5218-5221. Copyright (2007) American Chemical Society)...

It is well known that nanoparticulate colloidal dispersions of PANI in various paints at low concentrations cause tremendous improvements in corrosion protection [504]. PANI-NFs showed similar anticorrosive effects e.g., carbon steel coated with PANI-NFs has better corrosion protection than that with aggregated PANI. Raman spectroscopy analysis indicated that the surface of carbon steel coated with PANI-NFs formed a better passive layer, which is composed of a-ferric oxide and Fc304 [146]. The corrosion resistance performance of soya oil alkyd containing nanostructured PANI composite coatings has recently been studied [447]. An array of Fe nano wires within PANI-NTs was obtained using a two-step template synthesis [316]. This PANI-NT envelope may protect the Fe nanowires against a corrosive atmosphere. 

In the first case, the tip serves both as monomer (and electrolyte) dehvery tool and as the cathode for the electrochemical polymerization, while the conductive substrate is the anode. The polymerized material with a well-defined pattern and shape is subsequently deposited on the substrate. Many kinds of CPNWs, e.g. PPY, PANI, and PEDOT nanowires have been prepared with this approach on (semi-)conducting substrates e.g. silicon, graphite, or gold, using STM or conductive AEM tips [17-21]. Figure 10.8 is an AFM... 

With this method, single poly(p-phenylene vinylene) (PPV), PANI, and PPY nanowires have been synthesized and very narrow CPNWs with diameters as small as 5 nm have been demonstrated using DNA templates [60-63],... 

Peng et al. used fully enclosed nanochannels for the formation of single CPNWs [67,68]. Sub-lOO-nm silicon nitride nanochannels on a Si02/Si substrate were fabricated (Figure 10.28) [68]. PT and PANI nanowires (Figure 10.29) were prepared inside the nanochannels through chemical and electrochemical polymerization of the... 

Very recently, Yin et al. applied this expression in a transport study of individual PPY, PANI nanotubes, and PEDOT nanowires [99]. The authors also found that the temperature- and field-dependent I-V characteristics of these nanoscale materials can be fitted very well with the expression. 

It has been demonstrated that CPNWs are promising materials for the fabrication of a wide range of chemical and biological sensors. For example, a single PANl nanowire was reported to be able to detect ammonia gas at concentrations as low as 0.5 ppm with short response and recovery times (Figure 10.44) [80]. In another case, a single PANI nanowire detected ammonia gas down to a pressure of 10 bar (Figure 10.45) [84]. 

Kim et al. [118] electrodeposited 40-pm long, 100- or 200-nm thick PPy, PANI, and PEDOT nanowires on an Au surface using AAO templates with cylindrical nanopores. The diameters of the resulting nanowires were dictated by the pore sizes of the template used, with 100 nm pores resulting in 100 nm CP wires. The polymerization was initiated along the wall of the AAO template as the anionic template attracted cationic CP [131]. Consequently, instead of nanowires, nanotubes with wall thicknesses of 10-30 nm were formed initially. Then, as polymerization time increased, the nanotubes were filled to yield nanowires. 

PANI would be typically functionalized with selected dopants via either noncovalent or covalent approaches. In addition, nanostructured PANI materials, such as nanorods, nanowires and nanofibers, offer the possibilities to improve the performance of the PANI-based devices (Huang et al., 2003). PANI has demonstrated its biocompatibility in vivo and sparked great interests in tissue engineering. The biocompatibility of PANI can be further improved by the introduction of biocompatible elements without sacrificing its electric conductivity. 

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