Nanocomposite PANI/Clay

Performance improvement of polysulfone ultrafiltration membrane has been achieved by blending with PANI-NFs [457]. Conducting blends of nanostruetured PANI and PANI-clay nanocomposites with ethylene vinyl acetate as host matrix have been prepared [458]. A new conducting hybrid biocompatible composite material of PANI-NFs well dispersed in a collagen matrix was fabricated with various PANI-NFs/eoUagen ratios [459]. PANI-NFs doped by protonic acids can be efficiently dispersed in vinylidene fluoride-trifluoroethylene copolymers [460]. Fabrication of MWCNTs/PANI-NF nanocomposites via electrostatic adsorption in aqueous colloids has been reported [143]. A PANI-NFs/ carbon paste electrode was prepared via dopping PANI-NFs into the carbon paste [461]. 

Figure 14.12 Schematic of preparation (a) and the TEM image (b) of PANI/clay nanocomposite and flow curve (c) of fabricated PANI/clay nanocomposite particle-based ER fluid. Reprinted with the permission from Ref [89]. Copyright 2009 lOP Publishing.

Fang et al [89] have also used Pickering emulsion polymerization (Figure 14.12a) fabricate clay-coated PANI particles by employing exfoliated clay sheets as a stabilizer. PANI particles with a fairly broad size distribution indicate a quite rough surface, which is composed of exfoliated clay sheets (Figure 14.12b). The PANI/clay nanocomposite particles have been employed as an ER material and exhibit similar ER behavior (Eigure 14.12c) to other typical ER systems. 

It is known that conducting polymers provide beneficial protection to various kinds of metals in a corrosive environment [443-445]. Over the past decades, conducting polymers have been considered as the potential candidate for effective corrosion protection without the use of heavy metals. It was found that PPy-clay nanocomposites with low clay loading (e.g., 1.0 wt%) provided an enhanced corrosion protection effect on cold-rolled steel compared with pristine PPy [446]. Similarly, PANI-clay nanocomposites exhibited a better anticorrosion performance than conventional PANI [447]. In the... 

Akbarinezhad, E., Ebrahirru, M., Shar if, F Attar, M.M., and FaridL H.R. (2011) Synthesis and evaluating corrosion protection effects of emeraldine base PAni/clay nanocomposite as a barrier pigment in zinc-rich ethyl sibcate primer. Prog. Org. Coat., 70, 39-44. 

FIGURE 16 Schematic representation of two routes to the preparation of PANI-clay nanocomposites by in situ polymerization (A) adsorption of neutral aniline in Cu - or Fe -exchanged clays (B) ion exchange of interlayer cations with anilinium cations and subsequent polymerization with an oxidant agent (e.g., (NH4)2S20g). 

As presented schematically in Figure 16, a second way to prepare polymer-clay nanocomposites via in situ polymerization consists of intercalation of the monomer (or a precursor of the monoma-) in the form of a cation and then later addition of an initiator to induce/polymaization. Thus, the direct exchange of the interlayer cations of smectites by anilinium cations, followed by oxidation with (NH4)2S20g, could be an alternative procedure to reach the formation of PANI/clay nanocomposites. In this case, the expaimental conditions allow the direct formation of PANl as a conducting ema-aldine salt (152). 

Figure 8.5 Resonance Raman spectra excited at 632.8 nm and 488.0 nm of powdered samples of PANI-ES (A), PANI-MMT samples prepared from ex situ polymerization (B) and in situ polymerization (C). (Reprinted with permission from Macromolecules, Spectroscopic Characterization of a New Type of Conducting Polymer-Clay Nanocomposite by C. M. do Nascimento, V. R. L. Constantino and M. L. A. Temperini, 35, 20. Copyright (2002) ACS)...

Montmorillonite (MMT) is natural candidate for formation of nanocomposite due to special lamellar structure. In particular, the absorbed cation in interlayer provides ions exchange ability for intercalation of positive charged aniline monomer in the acid solution. Several approaches have been proposed to attempt to obtain ER active material based on PANI-intercalated MMT (PANI-MMT) nanocomposite [94-96]. Kim et al. [94] have introduced for the first time a kind of PANI-MMT (PANI-Na -MMT) nanocomposites as ER material. PANI-Na -MMT nanocomposite particles have been synthesized via emulsion polymerization. In the preparation, Dodecylbenzenesulfonic acid (DBSA) is used to disperse aniline monomer in xylene and then the clay colloid is added to form emulsion. 

Lu et al. [95] have also prepared ER fluid based on PANI-MMT nanocomposite with small particles diameter about 100-200 nm by an emulsion intercalation method. No additional surfactant is used and the aniline monomer remains excess amount in their intercalation reaction, and thus, the positive charged aniline monomer can well replace the absorbed sodium ions in interlayer of MMT. In order to further reduce the conductivity of the PANI-MMT particles prepared by the chemical oxidation of aniline in the presence of acidic dopant, the PANI-MMT particles must be immersed in NH aqueous solution. This immersed time for controlling conductivity of this nanocomposite is longer (several hours) compared with immersed time (only several minutes) of pure PANI. This may be related to the protection function of MMT layer to PANI macromolecular. The yield stress of PANI-MMT ER fluid is 7.19 kPa at 3 kV/mm, which is much higher than that of pure MMT as well as that of the mixture of PANI with clay (PANI+MMT). 

The effect of loading (0.5,1.0 and 2.0 wt%) nanostructured polyaniline (PANI) on the physiochemical, physicomechanical, morphological and thermal properties of soybean oil-based polyester nanocomposites has also been reported. The nanocomposites of conjugated linseed oil, acrylic acid and divinylbenzene are synthesised using modified montmoriUonite clay. The resultant nanocomposites exhibit a storage modulus in the range of 17-79 MPa at the glass transition temperature compared to the pristine polymer which is 2.1 MPa. The nanocomposites show better thermal stability (up to 200°C) than the pristine polymer. 

Polymer-clay nanocomposites using PANI and PPy exhibit better electrical behavior than PEO-clay systems, but in these cases the conductivity is electronic. These nanocomposites are prepared, as discussed earlier (Sec. V.B), by interla-mellar adsorption of aniline or pyrrole in smectites saturated with transition metal... 

The efficiency of DPA in anchoring the forming PANI chains layers has been explored in view of designing exfoliated clay-PANl nanocomposites [347]. In this work, instead of in situ generated diazonium, the diazotized DPA was first synthesized and intercalated with the bentonite clay by a cation exchange mechanism with sodium from the layered silicate. Such an intercalation increased the lamellar spacing between the bentonite lamellae and facilitated the in situ oxidative polymerization of aniline which resulted in exfoliation of the clay. The nanocomposite prepared... 

The research around the use of montmorillonite to obtaining nanocomposites polymer-MMT has become even more intense. In a review, Biswas and Ray [45] described several features of polymer-MMT nanocomposite materials. Ray and Okamoto [24] reported various characteristics of polymer-layered silicate nanocomposite materials, some of these materials exhibited distinctive properties like biodegradability. Ahmadi et al. [46] reviewed synthetic routes, properties, and future applications of polymer-layered nanocomposites. Significantly, nanocomposites of PAni and PPY with MMT clay via emulsion polymerization technique [47, 48] were found to act as electrorehological fluids, sometimes denominated smart fluids. In this context, Ballav and Biswas [49, 50] reported high yield oxidative polymerization of thiophene, aniline, pyrrole, and furan by MMT— without extraneous oxidant—vis-a-vis nanocomposites formation of the corresponding polymers with MMT. 

Hu et al. [55] Polyaniline/decavanadate-intercalated LDH modified (PAni/AD-LDH) The coating containing the nanocomposite offered better protection against corrosion than the polymer and clay coating did... 

Among the methods used for the addition of such fillers, only a small number of studies in the literature describe the preparation of these materials by in situ polymerization. Cho and coworkers [78] first utilized the in situ intercalative polymerization method for the preparation of polymer-clay nanocomposite consisting of conducting PAni and MMT. 

MMT is a clay naturally abundant and inexpensive, and due to its capacity to swell and exchange cations it is the most common inorganic matrix used for PAni composites [116-118]. Using anilinium intercalated clay (Ani-MMT) as precursor, it is possible to obtain a special type of nanocomposite when anilinium (Ani) polymerization is carried out mainly between the interlayer regions [119, 120]. 

The formation of intercalated and/or exfoliated nanocomposite is dependent on the monomer/clay ratio when aniline polymerization is performed in an acidic aqueous suspension of MMT in the presence of an oxidizing agent. If a small amount of PAni is present in the composite, conductivity of the material is still very close to that of pure MMT clay. In a critical amount of polymer and denominated percolation threshold [121], conductivity increases by several orders of magnitude with a small increase in the PAni amount. After reaching the optimum values, the value of conductivity starts decreasing and found very close to that of free PAni. On the oflier hand, nanocomposites of PAni-MMT [116, 118, 119] obtained by Ani-MMT polymerization show lower conductivity than fi ee PAni [117] and this fact can be attributed to the lack of connectivity between intercalated PAni chains [116, 118, 119] or a change in the nature of polymeric chains. 

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