Polymer dynamics in thin p-type conducting films investigated by ac-electrogravimetry. Kinetics aspects on anion exclusion, free solvent transfer, and conformational changes in poly(o-toluidine)

Abstract

A new transfer model is proposed to explain ac-electrogravimetry response of p-doped films. This model takes into account the exclusion effect occurring as a result of the anion transfer. The insertion/expulsion of anions inside a film involves simultaneously the expulsion/insertion of free solvent molecules. The number of solvent molecules excluded depends on the volume of anion transferred. Solvent transfer stimulated by the conformational changes of films constitutes the remaining electrogravimetric response when the exclusion process cannot explain by itself this response. Consequently, the kinetics of this free solvent transfer can be directly related to the kinetics of conformational changes. This model was validated in poly(o-toluidine) thin films where electrochemical kinetics were quantitatively investigated as a function of the applied potential. As far as we know, for the first time, charge transfer and conformational changes could be kinetically separated. This new transfer model may respond to fundamental questions on the electrochemistry of conducting polymers, which may have a significant impact on a large number of applications.