An electron-spin-resonance study of polyaniline and its derivatives: polymer interactions with moisture

The electronic behavior of polyaniline is sensitively dependent on moisture. For example, pumping under vacuum leads to an order of magnitude smaller conductivity, increased dielectric constant, and increased Curie susceptibility. An understanding of the mechanism of conductivity enhancement and changes in the other properties due to absorbed moisture thus requires better insight into the nature of the absorbed water. An electron spin resonance study has therefore been undertaken to find the various absorption/adsorption sites for water molecules. A number of experiments has been performed which lead us to propose a “variable-size metallic island” model. That is, protonated and highly ordered regions (metallic islands) are separated from unprotonated and amorphous regions by a less ordered region, whose width depends on the amount of moisture present in the sample. The water in the boundary region reduces its width by introducing order and thereby transforming partly localized polarons into bipolarons. The conductivity enhancement is argued to be due to increased size of the metallic islands in the presence of moisture.