Chronoamperometric Study of Conformational Relaxation in PPy(DBS)

Wireless electrochemical actuation of soft materials towards chiral stimuli

Different areas of modern chemistry, require wireless systems able to transfer chirality from the molecular to the macroscopic event. The ability to recognize the enantiomers of a chiral analyte is highly desired, since in the majority of cases such molecules present different physico-chemical properties that could lead, eventually, to dangerous or harmful interactions with the environment or the human body. From an electrochemical point of view, enantiomers have the same electrochemical behavior except when they interact in a chiral environment. In this Feature Article, different approaches for the electrochemical recognition of chiral information based on the actuation of conducting polymers are described. Such a dynamic behavior of π-conjugated materials is based on an electrochemically induced shrinking/swelling transition of the polymeric matrix. Since all the systems, described so far in the literature, are achiral and require a direct connection to a power supply, new strategies will be presented in the manuscript, concerning the implementation of chirality in electrochemical actuators and their use in a wireless manner through bipolar electrochemistry. Herein, the synergy between the wireless unconventional actuation and the outstanding enantiorecognition of inherent chiral oligomers is presented as an easy and straightforward read out of chiral information in solution. This approach presents different advantages in comparison to classic electrochemical systems such as its wireless nature and the possible real-time data acquisition.

Role of Polyoxometalate Contents in Polypyrrole: Linear Actuation and Energy Storage

A combination of polyoxometalates with polypyrrole is introduced in this work. Our goal was to include phosphotungstic acid (PTA) in different molar concentrations (0.005, 0.01, and 0.05 M) in the electropolymerization of pyrrole doped with dodecylbenzene sulfonate (DBS) and phosphotungstinates (PT), forming PPy/DBS-PT films. Scanning electron microscopy (SEM) revealed that the PPy/DBS-PT films became denser and more compact with increasing PTA concentrations. The incorporation of PT in PPy/DBS was analyzed using Fourier-transform infrared (FTIR) and energy dispersive X-ray (EDX) spectroscopy. The linear actuation in cyclic voltammetry and potential square wave steps in an organic electrolyte revealed increasing mixed actuation, with major expansion upon oxidation found for PPy/DBS-PT films with a PTA concentration of 0.005 M. Best results of a strain of 12.8% and stress at 0.68 MPa were obtained for PPy/DBS-PT (0.01 M). The PPy/DBS-PT films polymerized in the presence of 0.05 M of PTA and showed main expansion upon reduction, changing the actuation direction. Chronopotentiometric measurements of PPy/DBS-PT samples were conducted to determine the specific capacitance optimal for a 0.01 M PTA concentration in the range of 80 F g⁻¹ (±0.22 A g⁻¹).

Polypyrrole Polyethylene Composite for Controllable Linear Actuators in Different Organic Electrolytes

Controllable linear actuation of polypyrrole (PPy) is the envisaged goal where only one ion dominates direction (here anions) in reversible redox cycles. PPy with polyethylene oxide (PEO) doped with dodecylbenzenesulfonate forms PPy-PEO/DBS films (PPy-PEO), which are applied in propylene carbonate (PC) solvent with electrolytes such as 1-ethyl-2,3-dimethylimidazolium trifluoromethanesulfonate (EDMICF₃SO₃), sodium perchlorate (NaClO₄) and tetrabutylammonium hexafluorophosphate (TBAPF₆) and compared in their linear actuation properties with pristine PPy/DBS samples. PPy-PEO showed for all applied electrolytes that only expansion at oxidation appeared in cyclic voltammetric studies, while pristine PPy/DBS had mixed-ion actuation in all electrolytes. The electrolyte TBAPF₆-PC revealed for PPy-PEO best results with 18% strain (PPy/DBS had 8.5% strain), 2 times better strain rates, 1.8 times higher electronic conductivity, 1.4 times higher charge densities and 1.5 times higher diffusion coefficients in comparison to PPy/DBS. Long-term measurements up to 1000 cycles at 0.1 Hz revealed strain over 4% for PPy-PEO linear actuators, showing that combination of PPy/DBS with PEO gives excellent material for artificial muscle-like applications envisaged for smart textiles and soft robotics. FTIR and Raman spectroscopy confirmed PEO content in PPy. Electrochemical impedance spectroscopy (EIS) of PPy samples revealed 1.3 times higher ion conductivity of PPy-PEO films in PC solvent. Scanning electron microscopy (SEM) was used to investigate morphologies of PPy samples, and EDX spectroscopy was conducted to determine ion contents of oxidized/reduced films.

Comparative Analysis of Fluorinated Anions for Polypyrrole Linear Actuator Electrolytes

Either as salts or room temperature ionic liquids, fluorinated anion-based electrolytes have been a common choice for ionic electroactive polymer actuators, both linear and bending. In the present work, propylene carbonate solutions of four electrolytes of the three hugely popular anions-triflouromethanesulfonate, bis(trifluoromethane)sulfonimide, and hexafluorophosphate were compared and evaluated in polypyrrole linear actuators. The actuation direction, the characteristics-performance relations influence the behavior of the actuators. Isotonic Electro-chemo-mechanical deformation (ECMD) measurements were performed to study the response of the PPy/DBS samples. The highest strain for pristine PPy/DBS linear actuators was found in range of 21% for LiTFSI, while TBAPF6 had the least cation involvement, suggesting the potential for application in durable and controllable actuators. Interesting cation effects on the actuation of the same anions (CF3SO3-) were also observed.

Electrically Switchable Monostable Actuatoric Polymer-Based Nanovalve Arrays with a Long-Term Stability

Here we present a novel electrically switchable nanovalve array based on an intrinsic conductive polymer that has the capabilities to change its volume depending on its redox state. The polymer is created by anodic deposition of a sodium dodecylbenzenesulfonate (DBS)-doped polypyrrole (PPy). Optimization of the DBS-doped PPy layers revealed an actuatoric performance of up to 10% out of plane volume change. More interestingly, the electrochemical characterization revealed an actuatoric monostable polymer that could be used to fabricate nanovalve arrays that have a native opened state when no potential is applied and that can be closed when a reductive potential is applied. As a proof of concept, Atto488-labeled biotin (Biotin-Atto488) was used as a model compound and defined nanovalve arrays with nanopores in the range of 10 nm in diameter (opened state) were fabricated. Afterward, we were able to successfully prove the functionality of our nanovalve array by monitoring the flow-through rates of the Biotin-Atto488. More strikingly, we could demonstrate for the first time the robust and long-term stability of our nanovalve array without any performance loss for at least 72 h and retention capabilities of up to 90%. Furthermore, the demonstrated long-term stability was achieved under biocompatible conditions without the need of toxic dopant supplementation of the flow-through solution. Thus, our novel functional long-term stable nanovalve array offers the capabilities for practical applications.

The feasibility and application of PPy in cathodic polarization antifouling

Cathodic polarization antifouling deserves attention because of its environmentally friendly nature and good sustainability. It has been proven that cathodic voltages applied on metal substrates exhibit outstanding antifouling effects. However, most metals immersed in marine environment are protected by insulated anticorrosive coatings, restricting the cathodic polarization applied on metals. This study developed a conducting polypyrrole (PPy)/acrylic resin coating (σ = 0.18 Scm^-1), which can be applied in cathodic polarization antifouling. The good stability and electro-activity of PPy in the negative polarity zone in alkalescent NaCl solution were verified by linear sweep voltammetry (LSV), chronoamperometry (CA), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), demonstrating the feasibility of PPy as cathodic polarization material. Furthermore, the antifouling effects of PPy/acrylicresin coating on 24-h old Escherichia coli bacteria (E. coli) which formed on PPy/acrylic resin-coated plastic plate were measured under different cathodic potentials and treatment time, characterized by fluorescent microscope. The results suggest that at cathodic potential around -0.5 V (vs. saturated calomel electrode (SCE)), there was little trace of attached bacteria on the substrate after 20 min of treatment. PPy/acrylicresin-coated substrates were also subjected to repeated cycles of biofilm formation and electrochemical removal, where high removal efficiencies were maintained throughout the total polarization process. Under these conditions, the generation of hydrogen peroxide is believed to be responsible for the antifouling effects because of causing oxidative damage to cells, suggesting the potential of the proposed technology for application on insulated surfaces in various industrial settings.

Self-Supported Polypyrrole/Polyvinylsulfate Films: Electrochemical Synthesis, Characterization, and Sensing Properties of Their Redox Reactions

Thick films of polypyrrole/polyvinylsulfate (PPy/PVS) blends were electrogenerated on stainless-steel electrodes under potentiostatic conditions from aqueous solution. The best electropolymerization potential window was determined by cyclic voltammetry. After removing the film from the back metal, self-supported electrodes were obtained. Voltammetric, coulovoltammetric, and chronoamperometric responses from a LiClO4 aqueous solution indicated the formation of an energetically stable structure beyond a reduction threshold of the material. Its subsequent oxidation required higher anodic voltammetric overpotentials or longer chronoamperometric oxidation times. This structure was attributed to the formation of lamellar or vacuolar structures. X-ray photoelectron spectroscopy analysis of the films under different oxidations states revealed that the electrochemical reactions drive the reversible exchange of cations between the film and the electrolyte. The electrical energy and the charge consumed by the reversible reaction of the film under voltammetric conditions between the constant potential limits are a function of the potential scan rate, that is, they sense the working electrochemical conditions.

Hierarchical structure of hollow thorn-like polypyrrole microtubes with enhanced electrochemical performance

The hydrophilic sulfonate groups of SDBS were negatively charged, and were absorbed by the cationic pyrrole radicals produced during polymerization to PPy. The electrostatic absorption between the oppositely charged ions induced so-called thorns.

Characterization of conjugated polymer actuation under cerebral physiological conditions

Conjugated polymer actuators have potential use in implantable neural interface devices for modulating the position of electrode sites within brain tissue or guiding insertion of neural probes along curved trajectories. The actuation of polypyrrole (PPy) doped with dodecylbenzenesulfonate (DBS) is characterized to ascertain whether it can be employed in the cerebral environment. Microfabricated bilayer beams are electrochemically cycled at either 22 or 37 °C in aqueous NaDBS or in artificial cerebrospinal fluid (aCSF). Nearly all the ions in aCSF are exchanged into the PPy-the cations Na(+) , K(+) , Mg(2+) , Ca(2+) , as well as the anion PO4 (3-) ; Cl(-) is not present. Nevertheless, deflections in aCSF are comparable to those in NaDBS and they are monotonic with oxidation level: strain increases upon reduction, with no reversal of motion despite the mixture of ionic charges and valences being exchanged. Actuation depends on temperature. Upon warming, the cyclic voltammograms show additional peaks and an increase of 70% in the consumed charge. Bending is, however, much less affected: strain increases somewhat (6%-13%) but remains monotonic, and deflections shift (up to 20%). These results show how the actuation environment must be taken into account, and demonstrate proof of concept for actuated implantable neural interfaces.

Exchanged cations and water during reactions in polypyrrole macroions from artificial muscles

The movement of the bilayer (polypyrrole-dodecylbenzenesulfonate/tape) during artificial muscle bending under flow of current square waves was studied in aqueous solutions of chloride salts. During current flow, polypyrrole redox reactions result in variations in the volumes of the films and macroscopic bending: swelling by reduction with expulsion of cations and shrinking by oxidation with the insertion of cations. The described angles follow a linear function, different in each of the studied salts, of the consumed charge: they are faradaic polymeric muscles. The linearity indicates that cations are the only exchanged ions in the studied potential range. By flow of the same specific charge in every electrolyte, different angles were described by the muscle. The charge and the angle allow the number and volume of both the exchanged cations and the water molecules (related to a reference) between the film to be determined, in addition to the electrolyte per unit of charge during the driving reaction. The attained apparent solvation numbers for the exchanged cations were: 0.8, 0.7, 0.6, 0.5, 0.5, 0.4, 0.25, and 0.0 for Na(+), Mg(2+), La(3+), Li(+), Ca(2+), K(+), Rb(+), and Cs(+), respectively.

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.

Redox cycling for passive modification of polypyrrole surface properties: effects on cell adhesion and proliferation

The surface properties of electrodeposited poly(pyrrole) (Ppy) doped with sodium dodecylbenzenesulphonate (NaDBS) are modified by two methods: addition of poly(ethylene glycol) (PEG) during the electrodeposition and through redox cycling post electrodeposition. X-ray photoelectron spectroscopy (XPS) was used to ascertain PEG incorporation and to analyze the change in the oxidation state of the polymer. Anodic cycling resulted in the formation of micrometer-sized surface cracks which increased the amount of Rhodamine-B dye adsorbed onto the surface, and played a role in decreasing the wettability of the surface. The change in surface wettability caused by these cracks was mitigated by the presence of PEG in the Ppy matrix. Compared to the incorporation of PEG, redox cycling was more effective in passively modulating the adhesion of NIH 3T3 fibroblast cells on the Ppy surface. Based on the attenuation of surface polarity of the Ppy surfaces by the incorporated PEG, a mechanism is proposed to explain the observed cell adhesion behavior.