A simple model of polymeric relaxation, associated with the electrochemical switching of polypyrrole films between their reduced (insulating) and oxidized (electronically conducting) states, offers a reasonably precise description of the form of chronoamperograms obtained after previous subjection of the polymer film to cathodic potentials (which control the compactness of the neutral polymer) for long periods of time. The opening of the structure driven by the anodic potential is not uniform: nucleation of conducting zones inside the neutral polymer and their overlap at long times of anodic polarization are taken into account in the model. Diffusion of counterions from the solution across the oxidized zones is also included. The definition of a relaxation time (depending on both cathodic and anodic overpotentials and on temperature), and the inclusion of nucleation and diffusion processes, allows a theoretical simulation of chronoamperograms, in good agreement with experimental results from potential steps performed by changing the anodic and cathodic limits or at different temperatures.

The development of sensors with tactile sensitivity is one of the most exciting fields of research related to the development of interfaces between virtual reality and humans. The sensors developed must to be able to differentiate between hard and soft surfaces. Indeed, nature has developed muscles (actuators) with tactile sensitivity.Increasing effort is being devoted to the development of soft and wet devices, inspired by natural muscles, that are capable of transforming electric and/or chemical energy into mechanical energy.[1±8] The microfabrication of actuators containing a film of conducting polymers allows the construction of devices capable of manipulating an individual cell.[1±3]Gels, [4,5] elastomers, [6] co-polymers, [7] or nanotubes [8] can be supported on, or between, metallic layers for the development of actuators based on the electrophoretic, electro-osmotic, coulombic, piezoelectric, or electrostrictive properties of the polymeric materials. Devices based on conducting polymers as actuators, electromechanical devices, electrochemo-mechanical devices, or artificial muscles able to describe angular movements, from a few degrees to more than 360, or linear movements of a few micrometers have been proposed, constructed, checked, and revised.[9±17] We have participated in this effort with the construction of electrochemo-mechanical and macroscopic devices using films of polypyrrole (PPy) forming double layers [18,19] or triple layers [20±25] with a double-sided adhesive tape of a non-conducting and flexible polymer. In the triple layers, the current flows between two films of conducting polymer (Scheme 1): neither metallic components nor metallic counter-electrodes are required to manipulate the device. Devices able to trail up to 1000 times their own weight of steel attached to the end have been described. [21] In aqueous electrolytes, the flow of an anodic current promotes the oxidation of one of the films of conducting polymer by extracting electrons from the polymeric chain, changing the distribution of the double bonds and bond angles (conformations) and storing positive charges (radical cations or dications) along chains. These electrochemically stimulated conformational changes along the polymeric chains generate free volume: counterions (anions) and water penetrate from the solution in order to maintain electroneutrality, occupying the free volume and promoting the swelling processes.[26±29] A cathodic current flows through the second polypyrrole film, promoting the reverse processes and molecular movements. As a consequence, the polymer shrinks:The macroscopic change of volume induced by the continuous variation of the composition promotes increasing stress gradients (of expansion at the anode, of compaction at the cathode) across the conducting polymer/tape interfaces. As a consequence, the free end of the triple layer describes a continuous angular movement. Working under a constant current, the electrical energy consumed changes linearly [30] as a function of the chemical or physical vari...

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Following the hypothesis of the electrochemically stimulated conformational relaxation model (ESCRM), electrochemically generated films of poly(1-methylpyrrole), polythiophene, poly(3-methylthiophene), polyaniline, and polymethylaniline were studied by potential steps in lithium perchlorate/acetonitrile solutions. All the chronoamperograms studied by influence of different compaction potentials, or different temperatures, show a maximum, indicating the presence of conformational relaxation movements of the polymeric chains as kinetic-controlling processes of the electrochemical oxidation. Magnitudes as charge consumed to compact one mole of polymeric segments during cathodic polarization, the cathodic potential where the compaction of the polymers starts, the enthalpic increment between two stationary states defined by constant overpotentials of compaction and oxidation, and the diffusion constants stated at constant anodic overpotentials were obtained in the context pointed by the model for the studied polymers. The comparative study of the magnitudes for the different polymers, including similar magnitudes for polypyrrole and polyaniline from the literature, allows a comparative view of some structural, kinetic, and thermodynamic aspects, which can be useful for designing tailored properties, or applications, of the conducting polymers.

Oxidation/reduction reactions in films of conducting polymers exchanging anions and solvent during reactions are revisited here and explored by voltammetric and coulovoltammetric results using Pt electrodes coated with films of different polymers, in different solvents and salts. The reactions induce molecular (conformational) and macroscopic (relaxation, swelling, shrinking, and compaction) structural changes. Coulovoltammetric loops constitute a direct graphical tool to identify, separate, and quantify the structural components of the reversible film reactions together the potential domains and the charges involved in irreversible reactions. Any abrupt slope variation is related to abrupt changes of the reaction rate associated with each of the structural induced processes. Charges, energies, and characteristic potentials for any of the structural or irreversible process are obtained. Reversible film reactions are present from –1.5 to 0.35 V versus Ag/AgCl, overlapping the irreversible hydrogen evolution at the metal/polymer interface below –1.1 V. Structural reduction energies are higher than structural oxidation energies and structural changes are energetically asymmetric. 3D reactive structural memories are envisaged stepping up storage density by orders of magnitude. Conducting polymers are 3D structural gel reactors at the polymer chain level: large anions in solution cannot penetrate inside the film. Composition changes and structural processes mimic intracellular matrix (ICM) biological reactions.

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