A new model for electrochemical oxidation of polypyrrole under conformational relaxation control

Recent advances in the 3D printing of ionic electroactive polymers and core ionomeric materials

The recent advances in the 3D printing, or additive manufacturing, of ionic electroactive polymers (EAP) and their future applications.

Flexible hybrid film of polypyrrole incorporated chitosan as a biomimetic multistep electrochemical sensor of working temperature: a potentiodynamic study

A flexible polypyrrole/hydrogel hybrid film composed of macromolecular electrochemical machines is considered as a model material of the intracellular matrix of ectothermic muscle cells capable of sensing ambient thermal energy.

In Situ Measurement of Breathing Strain and Mechanical Degradation in Organic Electrochromic Polymers

Organic mixed ionic-electronic conductors (OMIECs) are an emerging family of materials crucial in the development of flexible, bio-, and optoelectronics. In electrochromic polymers, the cyclic redox reaction is associated with a mechanical breathing strain, which deforms the OMIECs and degrades the device reliability. We set forth an in situ nanoindentation approach to measure the breathing strain of a poly(3,4-propylenedioxythiophene) (PProDOT) thin film in a customized liquid cell during electrochromic cycles. A breathing volumetric strain of 12-25% is persistent in different sets of electrolytes of various solvents, salts, and salt molarities. The electrochemical conditioning, intermittence time, and cyclic protocol have minor effects on the mechanical response of PProDOT. The mechanical behavior and anion diffusivity measurement further infer the redox kinetics. Heavily cycled PProDOT films show reduced volumetric strain and accumulated mechanical damage of channel cracks and dysfunctional regions of slow and inhomogeneous electrochromic switching. This work is a systematic characterization of mechanical deformation and damage in a model OMIEC and informs the mechanical reliability of organic electrochromic devices.

Conjugated Polymer Actuators and Devices: Progress and Opportunities

Conjugated polymers (CPs), as exemplified by polypyrrole, are intrinsically conducting polymers with potential for development as soft actuators or "artificial muscles" for numerous applications. Significant progress has been made in the understanding of these materials and the actuation mechanisms, aided by the development of physical and electrochemical models. Current research is focused on developing applications utilizing the advantages that CP actuators have (e.g., low driving potential and easy to miniaturize) over other actuating materials and on developing ways of overcoming their inherent limitations. CP actuators are available as films, filaments/yarns, and textiles, operating in liquids as well as in air, ready for use by engineers. Here, the milestones made in understanding these unique materials and their development as actuators are highlighted. The primary focus is on the recent progress, developments, applications, and future opportunities for improvement and exploitation of these materials, which possess a wealth of multifunctional properties.

Synergistic interplay of ionic liquid and dodecyl sulphate driving the oxidation state of polypyrrole based electrodes

Herein, polypyrrole films are preparedviaelectrochemical deposition in a mixture of 1-n-butyl-3-methylimidazolium methanesulfonate ionic liquid and dodecy sulfate.

Self-Bleaching Behaviors in Black-to-Transmissive Electrochromic Polymer Thin Films

Polymer-based electrochromic smart windows are an emerging energy-saving technology. There are several technological hurdles in the development of organic electrochromics. In this article, the self-bleaching behaviors of a black electrochromic polymer (ECP-black) thin film were investigated. We found that the electrochemical break-in process led to a less dense morphology and the increased free volume facilitated ion permeation in the ECP-black thin films. The polarized interface between the polymer thin film and transparent indium-tin-oxide (ITO) electrode made charge transfer accessible, which caused the self-bleaching behaviors. Herein, we proposed two approaches to study and mitigate the self-bleaching phenomenon. First, a densely packed morphology was regenerated by increasing the cathodic polarization time under open-circuit conditions (V_off). The second involved the modification of the electrode (ITO) surface with a partial coverage of the octadecyltrichlorosilane layer. The combination of the two approaches rendered the ECP-black thin film capable of maintaining the colored state for up to 900 s. To extend the scope of our studies, self-bleaching of ECP-magenta and ECP-blue thin films were also tested and suppressed by using these two methods. Additionally, the cycling stability of the ECP-black has been improved from ∼600 cycles to up to 2300 cycles without a noticeable decay of optical contrast.

Reactions driving conformational movements (molecular motors) in gels: conformational and structural chemical kinetics

E_a,k,αandβfrom reactions driving molecular polymeric motors constituting dense gels include quantitative conformational and structural information.

Deep Reduced PEDOT Films Support Electrochemical Applications: Biomimetic Color Front

Most of the literature accepts, despite many controversial results, that during oxidation/reduction films of conducting polymers (CPs) move from electronic conductors to insulators. Thus, engineers and device's designers are forced to use metallic supports to reoxidize the material for reversible device work. Electrochromic front experiments appear as main visual support of the claimed insulating nature of reduced CPs. Here, we present a different design of the biomimetic electrochromic front that corroborates the electronic and ionic conducting nature of deep reduced films. The direct contact PEDOT metal/electrolyte and film/electrolyte was prevented from electrolyte contact until 1 cm far from the metal contact with protecting Parafilm(®). The deep reduced PEDOT film supports the flow of high currents promoting reaction induced electrochromic color changes beginning 1 cm far from the metal-polymer electrical contact and advancing, through the reduced film, toward the metal contact. Reverse color changes during oxidation/reduction always are initiated at the film/electrolyte contact advancing, under the protecting film, toward the film/metal contact. Both reduced and oxidized states of the film demonstrate electronic and ionic conductivities high enough to be used for electronic applications or, as self-supported electrodes, for electrochemical devices. The electrochemically stimulated conformational relaxation model explains those results.

Controlling the electro-mechanical performance of polypyrrole through 3- and 3,4-methyl substituted copolymers

A unique study of the impact of crosslinking on the electro-mechanical performance of electropolymerised polypyrrole films using laser-scanning micrometry.

Novel germanium/polypyrrole composite for high power lithium-ion batteries

Nano-Germanium/polypyrrole composite has been synthesized by chemical reduction method in aqueous solution. The Ge nanoparticles were directly coated on the surface of the polypyrrole. The morphology and structural properties of samples were determined by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Thermogravimetric analysis was carried out to determine the polypyrrole content. The electrochemical properties of the samples have been investigated and their suitability as anode materials for the lithium-ion battery was examined. The discharge capacity of the Ge nanoparticles calculated in the Ge-polypyrrole composite is 1014 mAh g⁻¹ after 50 cycles at 0.2 C rate, which is much higher than that of pristine germanium (439 mAh g⁻¹). The composite also demonstrates high specific discharge capacities at different current rates (1318, 1032, 661, and 460 mAh g⁻¹ at 0.5, 1.0, 2.0, and 4.0 C, respectively). The superior electrochemical performance of Ge-polypyrrole composite could be attributed to the polypyrrole core, which provides an efficient transport pathway for electrons. SEM images of the electrodes have demonstrated that polypyrrole can also act as a conductive binder and alleviate the pulverization of electrode caused by the huge volume changes of the nanosized germanium particles during Li⁺ intercalation/de-intercalation.

Structural electrochemistry. Chronopotentiometric responses from rising compacted polypyrrole electrodes: experiments and model

A model considering conformational packing and structural relaxation–swelling effects describes and quantifies chronopotentiometric responses from conducting polymer film electrodes.

Electropolymerized conjugated polyelectrolytes with tunable work function and hydrophobicity as an anode buffer in organic optoelectronics

A new class of conductive polyelectrolyte films with tunable work function and hydrophobicity has been developed for the anode buffer layer in organic electronic devices. The work function of these films featuring a copolymer of ethylenedioxythiophene (EDOT), and its functionalized analogues were found to be easily tunable over a range of almost 1 eV and reach values as high as those of PEDOT:PSS. The new buffer material does not need the addition of any insulating or acidic material that might limit the film conductivity or device lifetime. Organic photovoltaic devices built with these films showed improved open-circuit voltage over those of the known PSS-free conductive EDOT-based polymers with values as high as that obtained for PEDOT:PSS. Furthermore, the surface hydrophobicity of these new copolymer films was found to be sensitive to the chemical groups attached to the polymer backbone, offering an attractive method for surface energy tuning.

Biomimetic dual sensing-actuators based on conducting polymers. Galvanostatic theoretical model for actuators sensing temperature

A theoretical model is proposed for the quantitative description of the chronopotentiometric (E-t) responses, under galvanostatic control, of either conducting polymer films or dual sensing-actuating devices. Assuming that the reaction occurs by extraction, or injection, of n consecutive electrons from, or to, a polymer chain the material moves through n consecutive oxidation or reduction states. Stair functions are obtained describing either potential or consumed electrical energy evolutions as a function of both, driving (current) and environmental (temperature, electrolyte concentration...) variables. The current quantifies the actuation of any electrochemical device (charge/discharge of batteries, movement rate, and position of muscles): the stair functions are dual actuating-sensing functions. A good agreement exists between theoretical and experimental results from either polypyrrole films or artificial muscles at different temperatures. Only two connecting wires include, at any time, sensing (potential) and working (current) information of any dual device.

Reactive conducting polymers as actuating sensors and tactile muscles

Films of conducting polymers when used as electrodes in an electrolytic solution oxidize and reduce under the flow of anodic and cathodic currents, respectively. The electrochemical reactions induce conformational movements of the chains, generation or destruction of free volume and interchange of ions and solvent with the electrolyte giving a gel that reacts, swells or shrinks. Electric pulses acting on reactive gels constituted by polymers, solvent and ions are the closest artificial materials to those that constitute actuating biological organs. The electrochemical reaction under the flow of a constant current promotes a progressive change of color, volume, porosity, stored charge and storage or release of ions. The reaction is kinetically controlled by the conformational movements or by the diffusion of counterions through the gel; it works under electrochemical equilibrium and defines, at any intermediate oxidation state, equilibrium potentials. Any variable (mechanical, chemical, optical, magnetic, etc) acting on the equilibrium will induce a change in the working potential of any device, driven by a constant current, based on this reaction; actuating-sensing devices based on the electrochemical properties are expected. Artificial muscles able to sense pushed weights, electrolyte concentration or ambient temperature during actuation are described. The activation energy of the reaction includes structural information and allows the obtention of the conformational energy, the heart of both actuating and sensing properties.

In situ Electrochemical Fluorescence Studies of PPV

Conjugated phenylene-vinylene polymers are widely used in organic light-emitting and photovoltaic devices. The comprehension of the optical properties upon charge injection is of crucial importance for the improvement of such organoelectronic devices. The processes of electrochemical doping, electrolyte diffusion, and degradation have been studied by cyclic voltammetry and chronoamperometric methods. Kinetic studies by in situ fluorescence spectroscopy have been used for the determination of the mobility of charge carriers in the polymer making used of electrochemical Stern-Volmer analysis. The mobility of holes for MDMO-PPV measured by this method was 2.5 x 10(-7) cm2 V s(-1). Non-Faradic variations of the fluorescence after doping-dedoping cycles have been related to morphological changes in the polymeric layer. The evolution of the fluorescence obeys a first-order kinetics law, similarly to the trend of the variation of volume during gel shrinking.