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Conjugated conducting polymers, intrinsic conducting polymers or conducting polymers are complex and mixed materials; their electroactive fractions follow reversible oxidation/reduction reactions giving reversible volume variations to lodge or expel charge-balance counterions and osmotic-balance solvent molecules. The material content (reactive macromolecules, ions and water) mimics the dense intracellular matrix gel of living cells. Here the electropolymerization mechanism is reviewed highlighting the presence of parallel reactions resulting in electroactive and non-electroactive fractions of the final material. Conducting polymers are classified into nine different material families. Each of those families follows a prevalent reaction-driven exchange of anions or cations during oxidation/reduction (p-doping/p-dedoping or n-doping/n-dedoping). Polyaniline families also follow reaction-driven exchange of protons. The polymer/counterion composition changes for several orders of magnitude in a reversible way with the reversible reaction. The value of each of the different composition-dependent properties of the material also shifts in a reversible way driven by the reaction. Each property mimics another change in functional biological organs. A family of biomimetic devices is being developed based on each biomimetic property. Those electrochemical devices work driven by reactions of the constitutive material, as biological organs do. The simultaneous variation of several composition-dependent properties during the reaction announces an unparalleled technological world of multifunctional devices: several tools working simultaneously in one device. Such properties and devices are driven by electrochemical reactions: they are Faradaic devices and must be characterized by using electrochemical cells and electro-chemical methodologies.

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Polypyrrole coated gold wires were subjected to consecutive square current waves in LiClO4 aqueous solutions using the same constant anodic and cathodic charge. Parallel in situ diameter variations were followed using a laser scan micrometer. The procedure was repeated by changing one experimental variable every time: applied current, electrolyte concentration or working temperature to perform electrochemodynamical characterization of the system. On average, the diameter follows a linear variation of the consumed charge, as expected for any faradaic system, although a high dispersion was attained in the data. Such deviations were attributed to the presence of irreversible hydrogen evolution at the gold/polypyrrole interface at cathodic potentials more than 0.0 V vs. Ag/AgCl, detected and quantified from separated coulovoltammetric responses. Despite this parallel hydrogen evolution the consumed energy during reactions is a robust sensor of the working conditions. In conclusion a gold support, the metal most used for technological applications of conducting polymers, should be avoided when a device is driven by current flow in the presence of aqueous solutions, water contamination or moisture: a fraction of the charge will be consumed by hydrogen generation with possible degradation of the device.

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The electrochemical synthesis of a new dithienylcyclopentadienone-derivative/3-methylthiopene copolymer was performed by cyclic voltammetry. The obtained material shows redox processes very close to those from the pristine DTCPD. A new redox process at -1.24 V, with a large anodic shift (0.51 V) related to the poly(3-methylthiophene) reduction, indicates the existence of a copolymer with a strong influence of the neighboring (n-doped) DTCPD comonomer. The new copolymer is electrochemically n-doped at more cathodic potentials than -750 mV and p-doped at more anodic potentials than 250 mV, with a bandgap of 1.0 eV. The cation's entrance in the film from the solution during n-doping and anion's entrance during p-doping for charge balance was checked by QCM. The reduction of the DTCPD part suffers a partial trapping of the negative charges that can be reoxidized only at high overpotentials (>1 V related to the reduction potentials). After polarization of the material at any potential inside the band gap, subsequent p- or n-doping reactions performed by potential steps start by nucleation-relaxation kinetic control, followed by anodic or cathodic, respectively, chronoamperometric maxima. At the maxima, both reactions were checked to occur under chemical kinetic control, allowing the determination of the reaction orders for p- and n-doping processes.

RESUMEN

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.

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Understanding the lipid phase transition of lipid bilayers is of great interest from biophysical, physicochemical, and technological points of view. With the aim of elucidating the structural changes that take place in a DPPC phospholipid bilayer induced by an external isotropic surface pressure, five computer simulations were carried out in a range from 0.1 to 40 mN/m. Molecular dynamics simulations provided insight into the structural changes that took place in the lipid structure. It was seen that low pressures ranging from 0.1 to 1 mN/m had hardly any effect on the structure, electrical properties, or hydration of the lipid bilayer. However, for pressures above 40 mN/m, there was a sharp change in the lipid-lipid interactions, hydrocarbon lipid fluidity, and electrostatic potential, corresponding to the mesomorphic transition from a liquid crystalline state (L(alpha)) to its gel state (P'(beta)). The head lipid orientation remained almost unaltered, parallel to the lipid layer, as the surface pressure was increased, although a noticeable change in its angular distribution function was evident with the phase transition.

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The study of asymmetric lipid bilayers is of a crucial importance due to the great number of biological process in which they are involved such as exocytosis, intracellular fusion processes, phospholipid-protein interactions, and signal transduction pathway. In addition, the loss of this asymmetry is a hallmark of the early stages of apoptosis. In this regard, a model of an asymmetric lipid bilayer composed of DPPC and DPPS was simulated by molecular dynamics simulation. Thus, the asymmetric membrane was modeled by 264 lipids, of which 48 corresponded to DPPS- randomly distributed in the same leaflet with 96 DPPC. In the other leaflet, 120 DPPC were placed without DPPS-. Due to the presence of a net charge of -1 for the DPPS- in physiological conditions, 48 Na+ were introduced into the system to balance the charge. To ascertain whether the presence of the DPPS- in only one of the two leaflets perturbs the properties of the DPPC in the other leaflet composed only of DPPC, different properties were studied, such as the atomic density of the different components across the membrane, the electrostatic potential across the membrane, the translational diffusion of DPPC and DPPS, the deuterium order parameters, lipid hydration, and lipid-lipid charge bridges. Thus, we obtained that certain properties such as the surface area lipid molecule, lipid head orientation, order parameter, translational diffusion coefficient, or lipid hydration of DPPC in the leaflet without DPPS remain unperturbed by the presence of DPPS in the other leaflet, compared with a DPPC bilayer. On the other hand, in the leaflet containing DPPS, some of the DPPC properties were strongly affected by the presence of DPPS such as the order parameter or electrostatic potential.

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A molecular dynamic simulation of wet polypyrrole film was carried out, in both oxidized and reduced state. The system was modeled by two layers of polypyrrole, water and chloride ions (as counterions required for charge balance in the oxidized state) in atomic detail to provide an insight into some dynamic and steady properties of the system. Our simulations pointed to a swelling of the polymer matrix after oxidation due to electrostatic repulsions between charged sites of the oxidized polypyrrole, followed by penetration of the polypyrrole by counterions to maintain the electroneutrality of the system. Associated with this penetration of counterions toward the core of the oxidized polypyrrole, dehydration of the counterions was observed. This dehydration was compensated (in part) by a strong coordination with the charged sites of the polymer. The remaining hydrophobicity inside the polymer also contributed to the dehydration of these counterions. The translational diffusion coefficient of chloride ions was also calculated at different positions of the polypyrrole/water interface, from bulk water to the inner polymer matrix. A value of 4.1 x 10(-5) cm(2) s(-1) was measured in the bulk water compared to 5 x 10(-7) cm(2) s(-1) inside the polymer, representing a diminution of two orders of magnitude for the translational diffusion coefficient from bulk water to the core of a oxidized polypyrrole matrix. These results were in good agreement with experimental data.

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The movement of an all polymeric triple-layer artificial muscle based on polypyrrole (PPy) that work in aqueous solution was characterised. The magnitude and direction of the experimental current control both rate and direction of the movement. The described angle is a linear function of the consumed charge.

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