Nanostructured PPys

Using this approach Jang and coworkers166 have reported the synthesis of PPy nanoparticles at the 2 nm scale. Typical surfactants used in the preparation of these sub-5-nm particles were quaternary ammonium-based cations such as octyltrimeth-ylammonium bromide or decyltrimethylammonium bromide. Reactions at room temperature produced nanoparticles with diameters on the order of 10 nm, whereas at 70°C ca. 50 nm diameter particles were observed. 

Selvan and coworkers167168 utilized a block copolymer micelle of polystyrene-block-poly(2-vinylpyridine) in toluene exposed to tetrachloroauric acid that was selectively adsorbed by the micelle structure. On exposure of this solution to pyrrole monomer, doped PPy was obtained concurrently with the formation of metallic gold nanoparticles. The product formed consisted of a monodispersed (7-9 nm) gold core surrounded by a PPy shell. Dendritic nanoaggregate structures were also reported 

Monomer-containing Micelle J Polymer-containing Micelle 

FIGURE2.16 Schematic illustrating micellar/microemulsion nanoparticle synthesis. (With permission from G. G. Wallace and P. C. Innis, J. Nanosci. Nanotech. 2, 441 (2002). 2002, American Scientific Publishers.) 

PPy nanotubes have also been synthesized by inducing polymerization in an inverse microemulsion.169 Nanotubes were synthesized by using bis(2-ethylhexyl)sul fosuccinate (20.3 mmol) in hexane (40 mL), which form tubelike or rodlike micelles. The oxidant (FeCl3(aq)) is effectively trapped in the core of the micelle. Addition of pyrrole then results in interfacial polymerization at the micelle surface, resulting in hollow nanotubes 95 nm in diameter and up to 5 pm in length. The electrical conductivity of these nanotubes was up to 30 S cm-1. 

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Both gas sensors based on nontemplated and nanostructured PPy films were found to respond to a variety of solvent vapors, including methanol, ethanol, isopropanol, acetone, and also to humidity with a resistance increase. Initial tests were performed in ambient air leading to the observation of the following phenomenon, the sensors responded to water vapor with an immediate resistance increase, while exposure to organic solvents led to an initial small decrease in resistance before showing the... 

Biswas and Drzal integrated the polymerized nanostructure PPy with GNS in a directed self-assembly approach governed by the large van der Waal s force of attraction between the graphene basal plane and the tt... 

Wire-shaped growth of nanostructured PPy with diameter <10 nm, has been obtained by electropolymerization at naturally occurring step defects and artificially formed pit defects of HOPG, in a template assisted electropolymerization where the size of the nanostmctures could be controlled by limiting the pyrrole polymerization time at anodic potentials [242], Electrochemical polymerization of pyrrole within the confines of anodized alumina templates and subsequent metal nanoparticles immobilization on the surface of polymer pillars has been used to make surfaces that show roughness on two independently controllable levels sub-microscopic roughness from polymer pillar dimensions and nanoscopic roughness from the appropriate size selection of metal NPs [243],... 

A simple method was recently introduced for preparing core-shell nanostructured conductive PPy composite [45]. The PPy core particles were first introduced in flexible shell solutions by in situ polymerization, and then different core-shell structures could be obtained by the electrospinning method (Figure 4.12). In that study, PPy was selected as the as-dispersed phase (cores) and polyacrylonitrile (PAN) as the continuous phase (shell) the morphology of the resulted nanostructures can be controlled by changing the concentration of the solutions. This method is very useful in the design and preparation of nanosized core-shell structures using electroconductive polymers. 

Figure 4.12 Schematic illustration of the mechanism for preparing core-shell nanostructured conductive PPy composites. (Reprinted with permission from Materials Letters, Fabrication of Polyacrylonitrile/polypyrrole (PAN/Ppy) composite nanofibers and nanospheres with core shell structures by electrospinning by X. Li, X. Hao, H. Yu and H. Na, 62, 1155-1158.

To date, beside the conventional micro- and nanostructures that have been mentioned previously, there are numerous reports concerning other micro- and nanoarchitecmred CPCs, such as mesoporous, bowl-like, goblet-like, pipette-like structures, and so forth. Features such as high pore volume and high surface area allow mesoporous materials to serve as containers for foreign species [71 ]. A recent example of porous CPCs was reported by Cui [72], In their experiment, nanoporous PPy films were synthesized using a... 

Others have fabricated PPy nanowires by template-free potentiostatic polymerization in LiC104 and Na2C03 [3,4], which leads to the formation of disordered polymer mats at the electrode surface. These electrodes were used for the electrocatalytic reduction of nitrite and the oxidation of ascorbic acid. However, no comparisons were made between the nanostructured surfaces and bulk electropolymerized films. 

In addition to nanostructural properties of the conducting polymer, considerable influence on actuation behavior has been demonstrated due to the choice of electrolyte. This has included properties of the solvent employed, and crucially the size of doping ions and their interaction with the conducting polymer. As mentioned above, PPy films doped with moderately small anions (e.g. CP) lead to actuation driven by anion movement. By contrast, it is generally found that the inclusion of a large dopant anion (e.g. DBS) within PPy leads to cation-driven actuation, typically when a smaller cation is employed (e.g. Na ). However, it is not always a simple matter of predicting which movement, anion or cation, will predominate for a particular electrolyte system, and for a particular type of... 

Zhou et al. reported template-synthesized cobalt porphyrin/polypyrrole (TPPS-Co/PPy) nanocomposite and its electrocatalysis of oxygen reduction in a phosphate buffer solution (PBS) [97]. With the assistance of ultrasonication and different preparation procedures, the nanocomposite can be electrochemicaUy synthesized with uniform 2-D and 3-D nanostructures. Lines (a) and (b) of Figure 17.8 show the cyclic voltammograms of a cobalt... 

Secondly, appropriate orthogonal solvents for the selective template dissolution had to be found. Because of the same reason mentioned above, these solvents are not allow to even slightly swell the nanostructured conjugated polymers, otherwise the desired stractural features are inevitable lost. Diethyl ether and xylene were identified as ideal solvents for PEDOT and PPy, respectively. Chlorobenzene was reported to have no effect on the nanostructure of electrodeposited P3MT, but in this study the opposite was found [13]. Instead, pure diethyl ether or a 2 1 mixture of diethyl ether and hexane were used. 

Figure 7.3a shows the profound impact a so-called non-solvent for PT, such as chlorobenzene, can have on the nanostructure. Although chlorobenzene does not dissolve the polymer film, no obvious mesoporous nanostructure is left after template removal. This is most probably due to diffusion of solvent molecules into the conjugated polymer which destabilize the about 11 nm thick gyroidal network struts and eventually leads to the structural collapse. Using diethyl ether as solvent for the template dissolution instead resulted in mesoporous and highly ordered films. However, the free-surface did not show the same degree of order and porosity as the bulk of the film, see Fig. 7.3c. This behavior at the free-surface was more pronounced in the case of PEDOT and PPy, and will be discussed in more detail in the following to sections.

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