Polyaniline microstructures

Figure 9.8 (a) AFM and (b) LFM image of patterned PAN I films (Reprinted with permission from Applied Surface Science, Fabrication of patterned polyaniline microstructure through microcontact printing and electrochemistry by Fei Guan, Miao Chen, Wu Yangetal., 230, 1—4, 131-137. Copyright (2004) Elsevier ltd)... 

Since multiple electrical and optical luiiclioiialily must be combined in the fabrication of an OLED, many workers have turned to the techniques of molecular self-assembly in order to optimize the microstructure of the materials used. In turn, such approaches necessitate the incorporation of additional chemical fimctionality into the molecules. For example, the successive dipping of a substrate into solutions of polyanion and polycation leads to the deposition of poly-ionic bilayers [59, 60]. Since the precursor form of PPV is cationic, this is a very appealing way to tailor its properties. Anionic polymers that have been studied include sulfonated polystyrene [59] and sulfonated polyaniline [59, 60]. Thermal conversion of the precursor PPV then results in an electroluminescent blended polymer film. 

We have shown that the hexahydrous ferric chloride completely changes the microstructure of the blend. We observe a phase segregation creation of PVC nodules similar to the one formed by re-precipitation of PVC in the same conditions. A recent study [172] shows that in the case of polyaniline, the imine structure can be protonated with an acid HCl (by-product of the synthesis). The free water in the medium dissociates the acid, allowing the protonation of the chain, and explaining the increase in conductivity. This conductivity rise is about two decades when six water molecules are added for each molecule of FeClj, while the conductivity of the blend produced with FeCb, 6 H2O is lower than the one produced by anhydrous FeClj [127],... 

Y. Zhu, H. He, M. Wan, and L. Jiang, Rose-hke microstructures of polyaniline by using a simplified template-fiee method under a high relative humidity, Macromol. Rapid Common., 29,1705-1710 (2008). 

Figure 17.9 Cyclic voltammograms of electrochemical oxidation of ascorbic acid (A) a planar film composed of PAN/Au-NPs (B) a planar film composed of PAN/PSS (C) a bare Au electrode, in different concentrations of ascorbic acid (a) 0 mM, (b) 5 mM, (c) 10 mM, (d) 20 mM, (e) 30 mM, and (f) 40 mM. The data were recorded in 0.1 M phosphate buffer, pH 7.5. Oxygen was removed from the background solution by bubbling Ar. Potential scan rate, 5 mV s (Reprinted with permission from Chemistry of Materials, Enhanced Bioelectrocatalysis Using Au-Nanoparticle/Polyaniline Hybrid Systems in Thin Films and Microstructured Rods Assembled on Electrodes by E. Granot, E. Katz, B. Basnar and I. Wiliner, 17, 18, 4600—4609. Copyright (2005) American Chemical Society)...

Innovative microstructures have been produced by self-assembly during electropolymerization in the presence of surfactants. Dai and coworkers have recently shown that bowl-shaped microcontainers of polypyrrole can be produced by stabilizing H2 gas bubbles on the electrode surface [79]. Carboxylic acid dopants have also been used, resulting in hollow nanotubes of polyaniline [80]. 

Chan S, Kwon S, Koo TW, Lee LP, Berlin AA (2003) Surface-enhanced Raman scattering of small molecules from silver-coated silicon nanopores. Adv Mater 15 1595 Chen LL, Tang ZK, Shi MJ (2013) Microstructures and photoluminescence of electrochemically-deposited ZnO films on porous silicon and silicon. Key Eng Mater 538 30 Chiboub N, Boukherroub R, Gabouze N, Moulay S, Naar N, Lamouri S, Sam S (2010a) Covalent grafting of polyaniline onto aniline-terminated porous silicon. Opt Mater 32 748... 

Fig. 5 SEM images of polypyrrole nano- and microstructures after selective removal of porous silicon templates. Images (a-e) are related to polypyrrole, image (f) is for polyaniline, (d) is a magnified image of (b). Image (e) eorresponds to partially filled pores. Templates used are (a) ordered macropores and (c) mesopores while (b, d, e, f) medium-sized pores...

MIMIC has also been used to form patterned microstructures of polymers from their solutions in certain solvents that do not swell the PDMS mold. After filling the channels, the solvents were evaporated slowly by heating the samples in an oven. Figure 16 shows SEM images of patterned microstructures of PANI-ES produced from a PANl-EB solution in NMP [80]. After evaporating the solvent and removing the PDMS mold, the sample was immersed in an aqueous HCl (1 M) solution for 5 min to convert the polyaniline from the insulating form of EB into the conductive form of ES. 

Khuspe G. D., Navale T. Shankararao, Chougule A. Manik, et al. Facile method of synthesis of polyaniline-SnOj hybrid nanocomposites Microstructural, optical and electrical transport properties. Synth. Met. 178 (2013) 1-9. 

Dependence of Electrical and Optical Properties on the Morphology and Microstructure of Polyaniline... 

It is well known that the Bruggeman EMA formula is derived by considering one of the constituents as a small sphere. A deviation from such an assumption required a modification the formula to include depolarization factor. Typically, a value of 0.333 is used as a default value in the EMA layer, which assumes a spherical shape of the inclusion. The other two extremes are 0, for a needle-like or columnar micro structure, and 1 for flat disks or a laminar microstructure. This type of transition was found for polyaniline/poly(methylmethacrylate) blend films presenting with a spherical-like microstructure at low sample concentration, whereas at relatively high concentrations the depolarization factor shifted to values closer to 1. This indicated the formation of flat microstructures due to aggregation of the polyaniline particles [8]. 

Other applications of FTIR in microstructural analysis of homopolymers include 1,4-diazophenylene - bridged Cu-phthalocyanine [63], isobornyl methacrylate [64], polypropylene [65, 66], polyaniline [67, 68], polycaprolactone [69], viscose fibres [70], Kevlar [71], polystyrene sulfonic acid [66, 72], syndiotactic polystyrene [73], isotactic polypropylene [66,74,75], polyurethane [76], PMMA [75, 77], poljmrethane ether [78], PE [79-80], fluorinated acrylates [81], rigid PU [82], N-(2-biphenyl)4-(2 phenylethynyljphthalamide [83], polyacrylic acid [84], polysodium styrene sulfonate [84], and polyacrylic acid [85]. 

Applications of scanning electron microscopy (SEM) to polymer characterisation and microstructure include studies on the zwitterions-type polymer, poly(3-diethyl methylmethacryloyl ethyl) ammonium persulfonate grafted on to a silica surface by treatment of poly(2-dimethyl amino) ethyl methacrylate [2], polyaniline coated glass fibre fillers with different polyaniline contents [3], and also studies on ultra high molecular weight blends [4] and high-density polyethylene (HDPE)-gamma ferric oxide composite films [5]. 

The main classes of organic materials are as follows polyacetylene, polypyrrole, polyaniline, polyphenylene, and polythiophene. These materials share the characteristic that, on Ionic doping, electronic carriers are introduced into a delocalized ir system, rendering them very good conductors (98). As in the case of the oxides, this is a double-injection process, with counterions entering the poiymer structure. Several of the polymers can be produced by in situ electrochemical processes. Their microstructure is typicaiiy very dependent on preparation conditions. 

Polyaniline can be prepared electrochemically, and its microstructure depends on the preparative conditions (102). The charge capacity is comparable to the inorganic oxides Gottesfeld et al. (103) report a capacity of 800 C/cm in an aqueous acidic electrolyte and Genies et al. (102) a value of 450 C/g in propylene carbonate/LiCIO,j. 

The main diffraction peaks characteristic of PE are at about 20 = 21 and 24°. On the other hand, polyanihne synthesized via the falling pH route exhibits XRD peaks at about 20 = 6.5, 19 and 26° [23]. The position of the XRD peaks for PE did not change upon blending polyanihne with PE [47]. However, the intensity of the peaks decreased, indicating a lowering of the degree of crystallinity as the polyaniline composition in the blends increased [23, 47]. The 20 = 6.5 peak, characteristic of an interlayer repeat distance of alkyl tails of counterions that function as spacers between parallel planes of stacked polyaniline chains, was prominent in the spectra of polyaniline/ PE blends. The existence of this peak demonstrated that polyaniline had maintained its microstructure upon blending with PE [23]. 

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