“…Despite this observation, the predicted difference in formal potentials of 59 mV (eq 7) between the 0.01 and 0.1 M solutions is somewhat higher than the observed values. Our results show a smaller deviation from Nernstian behavior for PVF than reported previously. , We believe this is caused by differences in film history and experimental conditions. 5 6 …”
Section: Discussioncontrasting
confidence: 66%
“…Our results show a smaller deviation from Nernstian behavior for PVF than reported previously. 6,7 We believe this is caused by differences in film history and experimental conditions.…”
Section: Discussionmentioning
confidence: 99%
“…The simple model usually fails to fit experimental data well. Evans et al modified the simple model and introduced corrections for volume changes caused by redox switching and the mechanical energy connected with these changes. − Bard et al. , used a different model, assuming not one but a set of discrete E ° values to fit cyclic voltammetric data. Lang, Bacskai, and Inzelt used a transmission line model based upon two double-layer capacitances at each boundary of the film to explain anomalies in impedance spectra.…”
Cyclic voltammetry was used to create nonequilibrium populations of different solvation and configurational states of partially oxidized polyvinylferrocene (PVF). Oxidation levels were established by scanning either from a fully reduced state to the desired oxidation level or from a fully oxidized state to the desired level. Coulostatic conditions were then established by opening the external circuit, and subsequent mass and potential changes were followed. The film's approach to equilibrium involves configurational changes within the polymer and simultaneous and subsequent solvent transfer. At very short times (t e 0.2 s) the approach to equilibrium is limited by both solvation and reconfiguration processes. For a short time afterward (0.2 < t/s < 1.0) reconfiguration alone is rate limiting. At intermediate times (1 < t/s < 5) both processes play comparable roles. At long times (t > 5 s) solvation is the controlling step. The electroactive polymer film does not completely reach equilibrium even after 1 h at open circuit as evidenced by continuous small mass changes. These mass changes are the result of water transfer between the polymer film and the bathing electrolyte. A scheme of cubes model rationalizes mechanistic pathways leading to equilibrium. In particular, the observed extrema in mass (solvent population) are predicted. The electrode potential, after 1 h at open circuit, shows nearly Nernstian dependence on the redox composition for film states produced by either anodic or cathodic cyclic voltammetric scans. These Nernst plots are displaced by only a few millivolts because only a weak Nernstian dependence on film water content exists. Films that are 50% oxidized exhibit a sub-Nernstian response with respect to the perchlorate concentration in the bathing solution under permselective conditions.
“…Despite this observation, the predicted difference in formal potentials of 59 mV (eq 7) between the 0.01 and 0.1 M solutions is somewhat higher than the observed values. Our results show a smaller deviation from Nernstian behavior for PVF than reported previously. , We believe this is caused by differences in film history and experimental conditions. 5 6 …”
Section: Discussioncontrasting
confidence: 66%
“…Our results show a smaller deviation from Nernstian behavior for PVF than reported previously. 6,7 We believe this is caused by differences in film history and experimental conditions.…”
Section: Discussionmentioning
confidence: 99%
“…The simple model usually fails to fit experimental data well. Evans et al modified the simple model and introduced corrections for volume changes caused by redox switching and the mechanical energy connected with these changes. − Bard et al. , used a different model, assuming not one but a set of discrete E ° values to fit cyclic voltammetric data. Lang, Bacskai, and Inzelt used a transmission line model based upon two double-layer capacitances at each boundary of the film to explain anomalies in impedance spectra.…”
Cyclic voltammetry was used to create nonequilibrium populations of different solvation and configurational states of partially oxidized polyvinylferrocene (PVF). Oxidation levels were established by scanning either from a fully reduced state to the desired oxidation level or from a fully oxidized state to the desired level. Coulostatic conditions were then established by opening the external circuit, and subsequent mass and potential changes were followed. The film's approach to equilibrium involves configurational changes within the polymer and simultaneous and subsequent solvent transfer. At very short times (t e 0.2 s) the approach to equilibrium is limited by both solvation and reconfiguration processes. For a short time afterward (0.2 < t/s < 1.0) reconfiguration alone is rate limiting. At intermediate times (1 < t/s < 5) both processes play comparable roles. At long times (t > 5 s) solvation is the controlling step. The electroactive polymer film does not completely reach equilibrium even after 1 h at open circuit as evidenced by continuous small mass changes. These mass changes are the result of water transfer between the polymer film and the bathing electrolyte. A scheme of cubes model rationalizes mechanistic pathways leading to equilibrium. In particular, the observed extrema in mass (solvent population) are predicted. The electrode potential, after 1 h at open circuit, shows nearly Nernstian dependence on the redox composition for film states produced by either anodic or cathodic cyclic voltammetric scans. These Nernst plots are displaced by only a few millivolts because only a weak Nernstian dependence on film water content exists. Films that are 50% oxidized exhibit a sub-Nernstian response with respect to the perchlorate concentration in the bathing solution under permselective conditions.
“…[17][18][19][20][21] One of the most important conclusions of the work of Mauk and Moore 17 is that ''the possibility of redox state-dependent conformational changes should be considered''. Precisely, the idea of a redox potential being dependent on the state of tension (electron transfer/ deformation coupling) was introduced by Evans et al, [22][23][24] to explain the redox potential distribution of poly(vinylferrocene). The coupling of electron transfer, deformation, binding and electrostatic screening effects, was introduced to explain the redox potential distribution during the redox switching of arylamine substituted polymers.…”
Experimental data are presented demonstrating that electrochemically active macromolecules show a coupling among electron transfer, deformation, screening and binding. The work includes dependence of the redox potential of synthetic and natural electrochemically active polymers on the electrolyte pH (electron transfer-binding coupling), the changes in volume during the redox switching of synthetic electrochemically active polymers (deformation-electron transfer coupling) and the changes in the macromolecular conformation during the acid-base titration of polyelectrolytes and proteins (deformation-binding coupling). A simple equilibrium statistical thermodynamic model is presented that allows explaining these couplings effects. The model is based on the assumption that a macromolecule is composed of segments of different length that may bind species present in the external solution and that also contain redox centers that may be oxidized and reduced. The partition function of the system is obtained, and from it the expressions for the redox potentials, the total length and the chemical potential of the bound species are obtained. Simple calculations shows that the model satisfactorily explains the qualitative behavior of the experimental results.
“…3,4 Recently, considerable attention has been focused on conducting polymers, 5 which provide a great potential for the immobilization of biomolecules. The conductive/electroactive polymers such as polypyrrole (PPy), polyaniline, polythiophene were prepared by an electrodeposition, plasma polymerization, electropolymerization procedure, 6,7 and used as modifier for the construction of the chemically modified electrodes. Since PPy conducting polymer displays many interesting properties such as its convenience of preparation, redox activity, excellent conductivity, high thermal and mechanical stability, strong adsorptive capabilities towards macromolecules and maintains its conductivity for several months, 8,9 the different functionalizition of PPy provides a suitable interface of applications.…”
A novel simple immunosensing strategy for fabrication of hepatitis B surface antigen detection has been developed via electrochemical impedance spectroscopy (EIS) as a platform. At first, the conductive polymer polypyrrole (PPy) film was electrodeposited on a platinum electrode surface to adsorb the gold nanoparticles (nano-Au) via the opposite-charged adsorption technique, and then hepatitis B surface antibodies were adsorbed onto the surface of nano-Au. The modification procedure was characterized by EIS. Such spectroscopy is attributed to the concomitant conductivity changes of the polymerized pyrrole film and gold nanoparticles. The factors influencing the performance of resulting immunoelectrode were studied in detail. The linear range of the resulting immunoelectrode is from 2.6 to 153.6 ng•mL -1 with a detection limit of 1.3 ng•mL -1 at 3σ. In addition, the experiment results indicate that antibody immobilized on this way exhibits a good sensitivity, selectivity, high stability and a long-term maintenance of bioactivity, implying a great promising alternative approach for reagentless immunosensing analysis in the clinical diagnosis.
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