Loss Of Electroactivity Research Articles

Biodegradable Conducting PVA-Hydrogel Based on Carbon Quantum Dots: Study of the Synergistic Effect of Additives

Conductive hydrogels are becoming one of the most important milestones for the development of new scaffolds, biosensors, supercapacitors, and green electronics within the field of biomedicine. In this work, we study the effect of different types of electroactive additives such as poly(3,4-ethylenedioxythiophene), tannic acid, and carbon quantum dots (CQDs), to form different poly(vinyl alcohol) (PVA)-based hydrogels with enhanced electrochemical properties. Different physicochemical tests are carried out to characterize the different PVA-based hybrid hydrogels and the rates of their degradation and loss of electroactivity throughout an eight-week biodegradation process. This work shows the individual and synergistic effects of the additives on various mechanical properties, including storage modulus and swelling ratio, and electrochemical properties of the PVA hydrogel. The additives have proven to enhance the electroactivity of the PVA-based hydrogels but as well their degradation. Finally, the use of the new hydrogel as a pressure sensor is also investigated. The study provides an insight on the potential use of CQDs, in synergy with other electroactivity enhancers, in the fabrication of novel hybrid conducting hydrogels in green electronics.Graphical

Polysulfonate-doped polyanilines—oxidation of ascorbic acid and dopamine in neutral solution

The redox behavior of polyaniline (PANI) doped with polysulfonic acids is studied in slightly acidic and neutral solutions (from pH 4 to pH 7). The dopants used are polystyrene sulfonic acid (PSSA), poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA), and poly-(4,4′-(2,2′-disulfonic acid)-diphenylene-tere-phthalamide) (t-PASA). Thin PANI layers are used in order to identify clearly the redox peak structure. Based on deconvolution of the reductive currents, the pH dependence of the constituent peaks is studied and pathways of the reductive transitions are suggested. With increasing pH, a loss of electroactivity is observed for all three dopants but to a different extent: the largest for PAMPSA- and the smallest PSSA-doped PANIs. In the same time, a stabilization of the conductive emeraldine salt state is observed at pH 7 for all PANIs with the largest extent of stabilization in the PANI/PAMPSA case. The electrocatalytic properties of the polysulfonic acid-doped PANIs are comparatively studied for ascorbic acid (AA) and dopamine (DA) oxidation at pH 7. It is found that all three types of PANI are good electrocatalysts for both reactions with advantage of the PAMPSA-doped layers showing higher absolute oxidative currents for both reactions. The results concerning DA oxidation demonstrate the possibility to involve polysulfonic acid-doped PANIs in electrocatalytic reactions in neutral solutions occurring at high positive potentials beyond the peak potential of the PANI oxidative transition.

Effect of Structure of Polymeric Nickel Complexes with Salen-Type Ligands on the Rate of Their Electroactivity Decay in Solutions of Water-Containing Electrolytes

The influence of the structure of diimine bridge in the Schiff’s bases (derivatives of N,N'-ethylenebissalicylimine) on the rate of the loss of electroactivity of their complexes with nickel in acetonitrile containing 0.1 M of tetraethylammonium tetrafluoroborate (anhydrous and upon addition of 1 wt % of water) has been studied. It has been shown that the presence of bulky yet light methyl groups in the structure of diimine bridge significantly reduced the loss of electroactivity (37% of the initial capacity retained after 50 cycles) as compared to the ligand containing no substituents and containing phenyl group as the substituent (17 and 20%, respectively, of initial capacity retained after 50 cycles).

Multicolour Electrochromic Film Based on a TiO2@poly[Ni(salen)] Nanocomposite with Excellent Electrochemical Stability.

We report the electrochromic properties of a polymeric nanocomposite prepared by potentiodynamic deposition of transition-metal complex [Ni(3-Mesalen)], designated as [1], in the presence of TiO2 nanoparticles (NPs) with an average size of 9.7 ± 1.1 nm. Entrapment of TiO2 NPs in the poly[1] matrix was confirmed by several techniques. The nanocomposite TiO2@poly[1] films showed similar electrochemical responses to the original (nanoparticle-free) poly[1] films, but with higher electroactive surface coverages (Γ), showing the advantage of the nanocomposite preparation. The results indicated that the electronic structure of poly[1] was retained in the nanocomposite; nonetheless, a lower ε value was obtained for the charge-transfer band of the former, revealing superior stability of the nanocomposite for ligand high oxidation states. The TiO2@poly[1] nanocomposite showed interesting color changes, from yellow (reduced state) to green and russet (oxidized states), with enhanced electrochemical stability, demonstrated by a charge loss of only 7.3% over ca. 10 000 redox cycles surpassing the original polymer film stability: the loss of electroactivity is a factor of ca. 2 less than for pristine poly[1]. Furthermore, an enhancement of 16.7% in the optical modulation (ΔOD = 0.48) was also observed for the nanocomposite, confirming the benefit of TiO2 incorporation into the EC properties of the original polymer film.

Copper and nickel hexacyanoferrate nanostructures with graphene-coated stainless steel sheets for electrochemical supercapacitors

Copper and nickel hexacyanoferrate (CuHCF and NiHCF) nanostructures featuring three-dimensional open-framework tunnels are prepared using a solution-based coprecipitation process. CuHCF shows superior supercapacitive behavior than the NiHCF, due to the presence of numerous macropores in CuHCF particles for facilitating the transport of electrolyte. Both CuHCF and NiHCF electrodes with stainless steel (SS) substrate tend to lose their electroactivity towards intercalation/deintercalation of hydrated potassium ions owing to the partial corrosion of SS. Formation of a protective and conductive carbon layer in between SS and CuHCF (NiHCF) film is of paramount importance for improving the irreversible loss of electroactivity. Thin and compact graphene (GN) layer without observable holes in its normal plane is the most effective way to suppress the corrosion of SS compared with porous carbon nanotube and activated carbon layers. Specific capacitance of CuHCF electrode with GN layer (CuHCF/GN/SS) reaches 570 F g−1, which is even better than that of CuHCF with Pt substrate (500 F g−1) at 1 A g−1. The CuHCF/GN/SS exhibits high stability with 96% capacitance retention over 1000 cycles, greater than the CuHCF with Pt (75%).

Electrochemical and optical properties of poly(3,4-dimethylthiophene) and its copolymers with 3-methylthiophenein ionic liquids media

We present in this study the electrochemical properties of poly(3,4-dimethylthiophene) (PDMT) in comparison with poly(3-methylthiophene) (P3MT). The electropolymerizations were carried out at constant current densities (j=+2.5mA/cm2) in 1-ethyl-3-methyl-imidazolium bis(trifluoromethanesulfonyl)imide (EMITFSI) and N-butyl-N-methylpyrrolidiniumbis(trifluoromethanesulfonyl)imide (PYRTFSI). The electrochemical stability of PDMT has been considerably enhanced with the use of ionic liquids with a cyclability up to 1500 cycles in EMITFSI compared to only 100 cycles in acetonitrile and 0.1M tetraethylammoniumtetrafluoroborate (TBATFB). PDMT exhibits better electrochemical storage properties based on the measure of its specific capacitance (287F/g in EMITFSI) compared to P3MT (190F/g). The electrochemical reduction of doped PDMT is not complete as attested by UV–visible spectroscopic studies which showed the dual presence of transition bands of both neutral and polaronic species even after dedoping. This behaviour affects the doping/dedoping process of this polymer with loss of electroactivity whatever the ionic liquid used. Then, we performed the copolymerization at constant current densities from feed solutions containing the two monomers at different ratios. The evolution of the composition has been correlated to the continuous modulation of both electrochemical and optical properties. The oxidation potential of copolymers and the optical gap evolve according to the amount of DMT in the feed solution. Cyclic voltamperometry and UV–visible spectroscopy have confirmed that whatever the electrolyte (i) the copolymers have random composition and (ii) more DMT units are incorporated in the copolymer than DMT units initially present in the feed solution. The specific capacitance Cm of the copolymers increases with the amount of DMT from 190F/g to 287F/g in EMITFSI and from 230F/g to 279F/g in PYRTFSI at 30°C. The cyclability of copolymers is also improved compared to PDMT homopolymer. Therefore, this class of material is interesting in the field of electrochemical devices regarding the tunability of their electrochemical properties.

Clickable, versatile poly(2,5-dithienylpyrrole) derivatives

In this study a novel, clickable, azide containing conducting polymers based on 1-(2-azido-ethyl)-2,5-dithiophene-2-yl-1H-pyrrole (SNS-N3) were synthesized and characterized. Optical and electronic properties of homopolymer (PSNS-N3) were investigated and colorimetric studies were performed. The homopolymer has a band gap of 2.49eV and it displays yellow to blue coloration upon doping. Electrochemically prepared copolymers of SNS-N3 and 3,4-ethylenedioxythiophene (EDOT) formed multichromic, color tunable electrochromic materials with continuous color gradient from cinnamon, mustard, lime green, blue and dark blue. Spectroelectrochemical analyses revealed that the neutral copolymers possess two absorption maxima (∼320 and 450nm) where the relative intensity and position of the two depends on polymerization potential. Copolymer films could be fully switched between their neutral and oxidized forms in ∼1.2s with a percent transmittance of ∼65% at 950nm. Moreover, a PSNS-N3 coated ITO electrode was subjected to click reaction using ethynylferrocene. CV and FTIR studies revealed that ferrocene could easily be attached onto the electrode surface without loss of electroactivity of both ferrocene and PSNS backbone. Our results suggest that electrochemically prepared PSNS-N3 films offer a novel and multipurpose platform for simple, effective post-functionalization of poly(2,5-dithienylpyrrole)s under mild conditions.

Voltammetric and electrochemical gravimetric selective detection of interactions between Tl(I) and guanine and the influence on activity of DNA drug-intercalators

The interactions of Tl(I), a well known toxic species, with selected oligonucleotides were examined. The oligonucleotide sequences selected for the investigation were taken from gene hOGG1 responsible for repairing of DNA damage. Cyclic voltammetry was particularly useful, since nitrogen N-7 in guanine can be electrooxidized while its binding with Tl(I) leads to the loss of electroactivity. So, this selected interaction could be quantitatively used in drawing Scatchard's plot and calculating the binding constants and the number of active sites in guanine molecules occupied by one metal ion. Further, we have shown that the presence of Tl(I) leads to a decrease in activity of doxorubicin (DOX), a popular anticancer drug, vs. DNA. The obtained circular dichroism (CD) spectra and the measurements with an electrochemical quartz crystal microbalance (EQCM) led to a conclusion that in the presence of monovalent thallium cations the DNA double helix was neither damaged/oxidized nor its conformation changed substantially.

Impedance study of thiolated polyaniline

Covalent attachment of thiolated probes to conducting polymers such as polyaniline (PANI) is a promising approach towards the development of electrochemical sensors and biosensors. However, thiolation alters the conjugated polymer backbone and influences the electrochemical behavior of the conducting polymer. PANI studied in this work was electropolymerized on glassy carbon (GC) electrodes from a solution of 0.1 M aniline in 0.5 or 1.0 M H2SO4. The GC/PANI electrodes were then functionalized by covalent attachment of 2-mercaptoethanol to the PANI backbone. The progress of thiolation was studied by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Thiolation of PANI was found to cause an initial decrease in electroactivity at 0–0.25 V and an increase in electroactivity at 0.25–0.6 V. However, prolonged thiolation caused a loss of electroactivity of PANI, which could be seen from EIS measurements as a dramatic decrease in the bulk redox capacitance of PANI.

New insights into the characterization of poly(3-chlorothiophene) for electrochromic devices

Poly(3-chlorothiophene) has been prepared by anodic polymerization in boron trifluoride diethyl etherate with 0.1 M tetrabutylammonium tetrafluoroborate. The potential applied for the generation of the polymer has been found to affect considerably both physical (e.g. the thickness and roughness of the films, and the current efficiency) and electrochemical properties (e.g. the electroactivity, the doping level and the specific capacitance) whereas the density and the electrical conductivity remain practically unaltered in the interval ranging from 1.60 to 1.90 V. The dependence of the electrochemical behaviour with the generation potential has been explained by the morphological and topographical characteristics of the material, which have been investigated not only using scanning electron microscopy and atomic force microscopy but also electrochemical impedance spectroscopy. On the other hand, experimentally determined electronic properties have been reproduced by quantum mechanical calculations on model oligomers formed by up to 16 chemical repeating units that were arranged through a repetitive sequence of head-to-tail linkages. Oxidized and reduced poly(3-chlorothiophene) were found to be blue and Bordeaux red, respectively, the intensity of such two colors depending on the potential used for the generation of the film. Moreover, morphological changes induced by oxidation–reduction processes indicated that this polymer is a potential candidate for the fabrication of very stable electrochromic devices. Accordingly, an all-thiophene electrochromic device made of poly(3,4-ethylenedioxythiophene) and poly(3-chlorothiophene) has been successfully fabricated. This device has been proved to exhibit very remarkable redox stability: the loss of electroactivity is 65% of the initial value after 390 cycles and remains stable at such a value for more than 500 cycles.

Stability of conducting polyester/polypyrrole fabrics in different pH solutions. Chemical and electrochemical characterization

The stability of conducting fabrics of polyester (PES) covered with polypyrrole/anthraquinone sulfonic acid (AQSA) has been tested in different pH solutions (1, 7, 13) and after washing tests. It is important to determine the stability of the counter-ion in the polymer matrix, since its loss causes the decrease of the conducting properties of the fabrics. X-ray photoelectron spectroscopy (XPS) studies were done to quantify the amount of counter-ion in the polymer and to obtain the doping level (N δ+/N). Surface resistivity changes after the different tests were measured by electrochemical impedance spectroscopy (EIS). An increase in the solution pH caused a decrease of the doping level (N δ+/N), the release of part of the counter-ions and an increase in the surface resistivity. Cyclic voltammetry (CV) measurements showed a gradual loss of electroactivity as pH increased. The influence of the scan rate on the characterization of conducting fabrics has been also demonstrated by CV. Lower scan rates produce a more characteristic response than higher ones. Scanning electrochemical microscopy (SECM) measurements showed a loss of electroactivity when the sample was tested in the pH 13 solution, although the material continued being electroactive.

Copper-modified poly(3,4-ethylenedioxythiophene) layers for selective determination of dopamine in the presence of ascorbic acid: II Role of the characteristics of the metal deposit

The present study focuses on the specific role of the number, size, and shape of copper crystals electrodeposited on poly(3,4-ethylenedioxythiophene) (PEDOT) layers for the electroanalytic determination of dopamine (DA). It is shown that the type of the metal deposit is significantly influenced by the thickness of the polymer layer and the type of copper ions plating solutions, e.g., copper sulfate or copper oxalate. By combining electrochemical measurements and scanning electron microscopic investigations, it is found that the loss of electroactivity for DA oxidation, established for Cu deposited on thick PEDOT layers (from copper sulfate solution), relates to the instability of small needle-like Cu crystals decorating the PEDOT surface in this case. Large (several micrometer-sized) copper crystals (as deposited on thin PEDOT layers from copper sulfate solution) are found to suffer surface destruction along the crystalline edges when exposed to electrochemical treatment in the presence of DA. Finally, smaller (∼0.5 µm) bulky crystals with a large surface coverage (up to 30%), as deposited from copper oxalate solution, are found to provide a stable and highly sensitive Cu–PEDOT composite material operating in the nanomolar DA concentration range. Differential pulse voltammetry measurements carried out in the 6 nM to 2 µM DA concentration range, in the presence of large excess (1 to 5 mM) of ascorbic acid, show two regions of linear response with different sensitivities, 9 nA nM−1 and 0.313 µA µM−1, respectively.

Spectroscopic investigation and characterization of polypyrrole film doped with [MeN 4] 2[Ni(dmit) 2] complex salt

Polypyrrole doped with bis(1,3-dithiole-2-thione-4,5-dithiolate) nickellate (II) (PPy/[Ni(dmit) 2] 2−) was electropolymerized in acetonitrile solution and characterized by Fourier transform infrared (FTIR), ultraviolet–visible (UV–vis), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopies, as well as cyclic voltammetry (CV), conductivity, and scanning electron microscopy (SEM) measurements. Ionic desorption studies conducted by photon stimulated ion desorption (PSID) were also performed using synchrotron radiation at the S K-edge and time-of-flight mass spectrometry (ToF-MS) for ion analysis. The spectroscopic techniques indicated that the [Ni(dmit) 2] 2− was inserted onto the PPy backbone without modification during the electropolymerization process. Loss of electroactivity during the oxi-reduction processes indicated that the [Ni(dmit) 2] 2− leaves the film, undergoing anion exchange during the redox cycle. PPy/[Ni(dmit) 2] 2− exhibited higher intrinsic conductivity value than other PPy/M-dmit films studied previously. SEM measurements showed an irregular and heterogeneous surface with steps formation. PSID results showed that the species desorb through the X-ray induced electron stimulated desorption (XESD) mechanism while atomic sulfur species are mainly formed by Auger stimulated ion desorption (ASID). These results confirmed the presence of [Ni(dmit) 2] 2− at the topmost layers of the hybrid film.

Copper-modified poly(3,4-ethylenedioxythiophene) layers for selective determination of dopamine in the presence of ascorbic acid: I. Role of the polymer layer thickness

The oxidation of ascorbic acid (AA) and dopamine (DA) is studied on non-modified and copper crystal-modified poly(3,4-ethylenedioxythiophene) (PEDOT)-coated electrodes. Both oxidation reactions are studied for different thickness of the polymer layers. For several microns thick PEDOT layers both PEDOT and Cu-modified PEDOT show the largest currents. A stable voltammetric response for AA oxidation is observed together with a linear dependence of the peak currents on concentration in the 0.3 to 6.0 mM range. For DA oxidation, however, a gradual loss of electroactivity is found with increasing number of voltammetric scans and concentration. This problem is overcome by using thinner (<1 µm) polymer layers. In the presence of both AA and DA, the Cu-modified PEDOT-coated electrodes provide better selectivity with respect to DA in comparison to non-modified PEDOT due to partial suppression of the AA oxidation currents. Thin PEDOT layers modified with electrodeposited Cu crystals show a stable and sensitive response for DA oxidation in the micromolar concentration range. A linear dependence of the voltammetric peak currents is found in a wide concentration range (from 6 to about 200 µM) of DA in the presence of a large excess (1 mM concentration) of AA. The sensitivity is 0.013 µA µM-1.

Poly(3,4-(2-methylene)propylenedioxythiophene) for Electrochemical Grafting of Polystyrene via Methylene Functionality

A monomer 3,4-(2-methylene)propylenedioxythiophene (MProDOT) was synthesized and electrochemically polymerized to yield PMProDOT with methylene groups that have the potential to be further functionalized. Electrochemical redox switching of PMProDOT between −0.6 and +1.5 V (vs ) caused the cross-linking reaction between methylene moieties at the anodic potential limit and resulted in the fast decrease of electroactivity due to destruction of π-conjugation. When PMProODT was subjected to +1.5 V in the presence of styrene (ST) monomers, the loss of electroactivity was not significant and the mass of the PMProDOT was rapidly increased. The mass increase was ascribed to polystyrene (PST) grafting onto PMProDOT. Simultaneous oxidation of methylene groups and ST at +1.5 V led to the coupling of ST to PMProDOT, which reduced cross-linkable free-methylene moieties. PST-grafted PMProDOT showed relatively stable electroactivity over repeated potential cycling. The infrared spectrum of PST-grafted PMProDOT also showed additional C–H stretching peaks possibly due to PST grafting.

Sn Stability of Sn-Modified Pt Electrode for Reduction of Nitrate

This work investigated the stability of a Sn-modified Pt electrode for the reduction of nitrate using two type electrodes prepared by adsorption or electrodeposition of Sn onto Pt. In order to find the causes for the instability of the electrode, the effects of the condition of the solutions in which the electrode was used and the potential applied to the electrode on the electrochemical and metallurgical behaviors of the Sn on the Pt electrode were investigated. The Sn of the Sn-modified Pt electrode existed as a Sn hydroxide form, which brought about an easy loss of the electroactivity of the electrode in solution. During the reduction of nitrate, the electroactivity of the electrode was affected by the potential applied to the electrode. When a more negative potential than the redox potential between and Sn was applied, the Sn hydroxide was converted to Sn metal that was diffused into Pt, which led to a loss of electroactivity of the electrode as well. The solid diffusion of Sn increased linearly with the applied potential. The Sn-electrodeposited Pt electrode was more favorable for maintaining the integrity of the electrode during the electrolysis than the Sn-adsorbed Pt electrode.

Electrocatalytical properties of bergenin on a multi-wall carbon nanotubes modified carbon paste electrode and its determination in tablets

The electrocatalytic oxidation of bergenin is investigated on the surface of the multi-wall carbon nanotubes (MWCNT) modified carbon paste electrode (CPE) using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Using the modified electrode, the kinetics of the electro-oxidation of bergenin is considerably enhanced, by lowering the anodic overpotential through a catalytic effect. In the following anodic sweep from 0.1 to 0.9 V, bergenin adsorbed at MWCNT modified CPE surface yielded a sensitive oxidation peak at 0.614 V. The anodic peak potential (Epa) shifts negatively of 135 mV when compared with that on bare CPE. Due to its unique structure and extraordinary properties, MWCNT shows higher electrocatalytic efficiency toward bergenin. A linear dynamic range of 6.0 × 10−7 to 1.0 × 10−5 M for bergenin is obtained in phosphate buffer solutions (PBS) of pH 7.0, the linear regression equation is expressed as Ipa (μA) = 0.0430c (μM) + 0.0318, r = 0.9989 and the detection limit is 7.0 × 10−8 M after 3 min open-circuit accumulation. The relative standard deviation of 1.0 × 10−6 M bergenin in 10 successive scans is 1.6% for the same electrode and 2.0% for interelectrodes, indicating excellent reproducibility. The modified electrode exhibited a high stability when it was placed in dry state. No loss of electroactivity of the electrode was found for the continuous cyclical sweep for 6 h and the modified electrode was also not deteriorated even for 3 weeks. The influence of various interferences on the response of 1 μm bergenin presented a small signal change. Bergenin has been successfully detected in tablets and the recovery ranges from 99.8% to 100.2%. High sensitivity and selectivity together with low detection limit of the electrode response make it very suitable for the determination of trace amounts of bergenin in pharmaceutical and clinical preparations.

Charge compensation dynamics in a soluble copolymer of poly(aniline) and poly(phenylene sulfide)

Poly(phenylene sulfide phenyleneamine), PPSA, is a copolymer of poly(aniline) and poly(phenylene sulfide), soluble in conventional organic solvents as tetrahydrofuran, dimethyl sulfoxide, dimethylformamide, and cyclohexanone. In this research, its electrochemical behavior has been studied in acetonitrile in the presence of different electrolytes, where the loss of electroactivity was observed after few cycles. In this paper, the charge compensation dynamics of PPSA is analyzed through electrochemical quartz crystal microbalance experiments and electroacoustic impedance measurements. Raman spectroscopy data have shown that once the oxidation of the sulfur atom occurs, a loss of electroactivity is observed, being not possible to recover the pristine state of the polymer. Fourier transform infrared (FTIR) and X-ray diffraction (XRD) data obtained for the fully oxidized polymer are consistent with the formation of a networked polymer due to the electrophilic attack of the positive sulfur atom on the activated aromatic rings. Electrochemical quartz crystal microbalance results clearly show that the degree of irreversibility fully depends on the chemical nature of the anions with a negligible participation of the cations of the electrolytic solution.

Spectroelectrochemical study of a soluble derivative of poly(aniline) in a room temperature ionic liquid

Poly(phenylene sulfide phenyleneamine), PPSA, is a soluble copolymer of poly(aniline) and poly(phenylene sulfide). Its electrochemical behavior has already been studied in both aqueous and organic media in the presence of different electrolytes, where it was observed the loss of electroactivity after few cycles. In this paper, the spectroelectrochemical characterization of PPSA films in a room temperature ionic liquid (RTIL), 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanes sulfonyl)imide (BMMITFSI), is shown. The electrochemical response of a PPSA modified electrode in BMMITFSI is different from that obtained in organic solvent/salt systems. In RTIL, two reversible redox processes were observed and they were assigned to the reversible radical cation/dication transition based on “ in situ” UV–vis and Raman spectroscopic studies. The stabilization of the dicationic species in RTIL is an explanation for the reversible electrochemical response of the PPSA in BMMITFSI; on the contrary, when the electrochemical oxidation is carried out in conventional organic electrolytes, once the oxidation of the sulfur atom occurs, a loss of electroactivity is observed being not possible to recover the pristine state of the polymer. FTIR and XRD data obtained for the fully oxidized polymer in acetonitrile are consistent with the formation of a networked polymer due to the electrophilic attack of the positive sulfur atom on the activated aromatic rings. It is not the case in RTIL due to the shielding of the charged sulfur atoms avoiding its reaction to other chains to form the networked polymeric matrix.

Electroconductive Hydrogels: Electrical and Electrochemical Properties of Polypyrrole‐Poly(HEMA) Composites

AbstractComposites of inherently conductive polypyrrole (PPy) within highly hydrophilic poly(2‐hydroxyethyl methacrylate)‐based hydrogels (p(HEMA)) have been fabricated and their electrochemical properties investigated. The electrochemical characteristics observed by cyclic voltammetry suggest less facile reduction of PPy within the composite hydrogel compared to electropolymerized PPy, as shown by the shift in the reduction peak potential from −472 mV for electropolymerized polypyrrole to −636 mV for the electroconductive composite gel. The network impedance magnitude for the electroconductive hydrogel remains quite low, ca. 100 Ω, even upon approach to DC, over all frequencies and at all offset potentials suggesting retained electronic (bipolaronic) conductivity within the composite. In contrast, sustained application of +0.7 V (vs. Ag/AgCl, 3 M Cl−) for typically 100 min. (conditioning) to reduce the background amperometric current to &lt;1.0 μA, resulted in complete loss of electroactivity. Nyquist plots suggest that sustained application of such a modest potential to the composite hydrogel results in impedance characteristics that resembles p(HEMA) without evidence of the conducting polymer component. PPy composite gels supported a larger ferrocene monocarboxylate diffusivity (Dappt=7.97×10−5 cm2 s−1) compared to electropolymerized PPy (Dappt=5.56×10−5 cm2 s−1), however a marked reduction in diffusivity (Dappt=1.01×10−5 cm2 s−1) was observed with the conditioned hydrogel composite. Cyclic voltammograms in buffer containing H2O2 showed an absence of redox peaks for electrodes coated with PPy‐containing membranes, suggesting possible chemical oxidation of polypyrrole by the oxidant