Dr. Bernhard Wessling
Ormecon Chemie                                                Synthetic Metals 102 (1999) 1396-1399

Dispersion shifts Polyaniline to the metallic side of the "Insulator-to-Metal(1M)-Transition" / Crystal structure revealed

This is the abstract of an oral presentation, presented at ICSM 98 in Montpellier.
The full text is available as a preprint version on request.

Full paper to be published

Conductive Polymers like Polyaniline are principally insoluble, which can be deducted from several basic thermodynamical considerations. Therefore, dispersion is the appropriate way of processing ICPs and PAni. We have shown earlier, that certain thermoplastic blends of PMMA (60%) and polyaniline (40%) have been 10 times more conductive than the starting raw PAni powder, had a partially metallic conductivity/termperature dependance and a much higher reflectance, although PAni was the minor component. The Morphological nanostructures responsible for this will be shown.

Low temperature conductivity measurements and the calculation of the reduced activation energy [W = dln(sigma) / dln(T)] showed, that these blends are clearly on the metallic side of the IM transition, whereas the starting raw powder is on the insulator side. This is the first time, that polyaniline was found there reproducibly and under ambient conditions. We have analyzed the reasons for this change and found, that one prerequisite is a very high - the highest ever found in ICPs - density of states at the Fermi energy, the other is dispersability, and the dispersion step leads to a new crystal structure of PAni.

The crystal structure of Polyaniline will be shown, both the "pre-metallic" form (undispersed), and the metallic form (dispersed), and their dramatic difference will be explained. The (commercial) dispersion process is obviously accompanied by a shear induced re-crystallization.

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