Electrochemically Induced Volume Changes in Poly(3,4-ethylenedioxythiophene)

Abstract

The electrochemical properties of poly (3,4-ethylenedioxythiophene) are studied using the bending beam method to detect volume changes during electrochemical transformations of the material. Thin films of poly (3,4-ethylenedioxythiophene) immersed in different supporting electrolytes first contract very rapidly and then expand on doping, while upon undoping they contract directly, or first expand and then contract, to their original positions. It is clearly observed that the oxidation or reduction of the polymer contains two steps, one due to a redox potential close to -0.5 V vs Ag/AgCl, and another potential around 0 V. We find that the volume changes cannot be understood as a simple consequence of ion transport but must be due to the structural change of the polymer between the different states. A hypothetical picture is that during the transition from the neutral to the polaron state, the polymer is slightly charged and thus contracted; on further doping to the bipolaron and to the metallic state, the coulomb repulsion between charged sites become stronger, and the polymer expands.

Electrochemistry of Poly(3,4‐alkylenedioxythiophene) Derivatives

“…There is also a report on the volume change of PEDOT induced by electrochemical p-doping. [99] The doping process induces expansion of the polymer in agreement with the mass increase recorded by EQCM. [63] In-situ conductivity measurements performed in ACN + 0.1 M Bu 4 NClO 4 [63] show that oxidation causes the transition from a low conductive to a conductive state as generally found in conjugated polymers.…”

Electrochemically induced free solvent transfer in thin poly(3,4-ethylenedioxythiophene) films

“…the exclusion effect can be neglected in this potential range. As the doping level increases, the coulomb repulsion between charged sites becomes stronger, forcing the polymer to expand [48].…”

“…The number of free water molecules excluded by anion ( ) is assumed constant at 4.7 in the overall studied potentials. However, the transfer of water molecules in both direction ( and ) increases as PEDOT is oxidized owing to the swelling of PEDOT structure [48]. At potentials where PEDOT is doped, the number of water molecules transferred is about 60.…”

“…The resulting charge defects are compensated with the insertion increasing the polarity of PEDOT [48]. This fact involves a mechanical accommodation of charged polymeric chains and stored anions inside the PEDOT film by repulsive interactions (eq (27) …”

Electronic Control of Cell Cultures Using Conjugated Polymer Surfaces

“…Volume changes during redox cycling have been studied extensively for polypyrrole [33,34,54] and to a lesser extent for PEDOT. [64,65] The expansion is associated with the insertion of ions and solvent for charge compensation during doping and de-doping of the polymer (figure 3.6). When using a large immobile anion in a p-doped polymer, expansion will occur when reducing the polymer as cations from the electrolyte are needed for charge compensation.…”