Polyaniline dilute polymerization

The nanofibrous structures prepared from dilute polymerization have no significant change when dedoped and redoped multiple times by base and acid solutions, respectively. The dispersion in deionized water of nanofibers is stable for several minutes without aggregation and precipitation [239]. Furthermore, a highly porous film of nanofibers is obtained as the dispersion is cast and dried on the glass or silicon wafer substrates. The UVA is absorption patterns of polyaniline nanofibers obtained are consistent with previously reported results for conventionally synthesized polyaniUne. 

FIGURE 46.42. Nanofiber network of polyaniline prepared by dilute polymerization. Reprinted from [243] (2005) with permission from Wiley-VCH. 

N. R. Chiou, A. J. Epstein, Polyaniline nanofibers prepared by dilute polymerization, Advanced Materials 2005, 17, 1679. 

High quality thin films of doped polypyrrole and doped polyaniline can be conveniently deposited during a few minutes at room temperature on glass and plastic substrates from dilute aqueous solutions of the respective monomer as it undergoes oxidative polymerization (5-5,75). We find that the deposition rate and the properties of the films are greatly dependent on the nature of the substrate surface, e.g., whether deposited on hydrophilic or hydrophobic surfaces. 

The preponderance of patent or sdentific literature regarding polyaniline synthesis in aqueous media reports synthetic conditions whereby the concentration of the acid is measurable on the pH scale and the acid most frequently reported is HCl. The activity and concentration of the hydronium ion are obtained by measurements of pH by ion-selective electrodes or pH paper-containing indicators. However, such pH measurements are valid only in single-solvent systems, typically water, for very dilute concentrations of an acid. However for very concentrated add solutions, such as those used to polymerize aniline at subzero temperatures, the preferred measure of the ability of an acid to dissociate a proton from an indicator, according to HB+ H+4-B, is the Hammett acidity function, Hq given by... 

The in situ polymerization of aniline to form an electrically conductive textile was also first reported by Kuhn and coworkers [78,79] in which the polyaniline was deposited onto a textile substrate from an aqueous solution containing aniline, ammonium persulfate, hydrochloric acid, and either the disodium salt of 2,6-naphthalenedisulfonic acid or 1,3-benzenedisulfonic acid. In these studies, the polymerization conditions were controlled in order to deposit the polyaniline layer only onto the textile support with no polymer precipitating in the bulk liquid phase. This was accomplished by using dilute solutions of aniline (0.03 M). A subsequent study by Tzou and Gregory [92] on the deposition of polyaniline to nylon-6 fibers was focused on investigating the reaction kinetics of the chemically oxidative polymerization of aniline... 

The conventional chemical polymerization of polyaniline only produces nonfibrous or irregular shaped morphologies [237,238], In the past several years, a variety of chemical methods were reported that yield polyaniline nanofibers, such as use of hard templates [239,240], soft templates [241], electrospinning [242], interfacial polymerization [237], and seeding polymerization [238]. Recently, Chiou and Epstein discovered that polyaniline nanofibers can be directly synthesized in dilute chemical polymerization... 

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