Solvent-induced microstructure changes and consequences for electrochemical activity of redox-active conducting polymers

Electrochemical impedance spectroscopy (EIS) was used to demonstrate solvent-induced collapse of the microstructure of redox-active conducting polymers; the collapse was dependent on the nature of the polymer and had a significant effect on the redox activity of the materials. Conducting polymer films of terthiophene, poly(3-((2′:2″,5″:2‴-terthiophene)-3′′-yl) acrylic acid) (PTAA) and poly(3,4-ethylenedioxythiophene) (PEDOT) were produced in an organic solvent (DCM, dichloromethane) and subsequently immersed in other organic solvents (DCM, acetonitrile) or in an aqueous solution (Tris buffer). Impedance diagrams over time implied shrinkage of the polymer upon solvent change, particularly in Tris buffer, that was more pronounced and more rapid for PTAA than for PEDOT. These changes were correlated with a loss of reversibility of electrochemical cycling and an increase of potential required for ion insertion into the polymer and could simply be understood in terms of the change in solvation of the polymer.