A5. Electro- and chemochromic Applications

Potential applications based on the different colors of ICPs linked with their different oxidation states have been worked on since long time. PAni, for example, is green in its “doped” metallic salt form, blue in the neutral base form, and colorless in the reduced stage (fig. 4.1 - 4.4). One can switch between these stages by either applying a certain voltage, or with appropriate chemical agents (acids, bases, reductive or mild oxidative agents, resp.). Electrochromic windows, sensors, indicators or else could be realized. For an overview, see [1].

Up to now, no significant applied oriented development has taken place, at least as far as been published. Several announcements did not come true.

For future development, it might be interesting, that some blends which are used for transparent coatings (cf. A 1.) are responding to electrochemical switching of oxidation states (and hence color) at least as quick as pure PAni [2]. Coatings from blends or from pure dispersions are easily applied and will serve as technically fully satisfying and commercially attractive processing tools. Direct polymerization on ITO glass is actually preferred by R&D groups, but will not be reproducible enough and not at all competitive to dispersion or blend coating techniques, due to difficult process control, purification and chemical waste problems in factories, where chemical processes are usually not practiced.

List of Figures:

fig 4.1-4.4: Spectra of polyaniline, (1) emeraldine salt, as polymerized (2) neutral emeraldine base (3) reduced leucoemeraldine form (4) emeraldine salt, after reduction and re-oxidation.

Footnotes

[1] A. Hugot-Legoff, “Electrochromism in polyaniline”, in: Handbook of Organic Conductive Molecules and Polymers, edited by H.S. Nalwa, Vol. 3 (1997) 745-782

[2] A. Weppner, personal communication

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