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Copyright of Orthodontie Française is the property of John Libbey Eurotext Ltd. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Constant-Phase Elements (CPE) are often used to fit impedance data arising from a broad range of experimental systems. Four approaches were used to interpret CPE parameters associated with the impedance response of human skin and two metal oxides in terms of characteristic frequencies and film thickness. The values obtained with each approach were compared against independent measurements. The power-law model developed recently by Hirschorn et al. provided the most reliable interpretation for systems with a normal distribution of properties. Readers are cautioned that the CPE parameter Q does not provide an accurate value for capacitance, even when the CPE exponent α is greater than 0.9. [ABSTRACT FROM AUTHOR]

This work was devoted to probe, at the entire population level, interactions between mucins and Lactococcus lactis, using QCM-D. Real-time monitoring of adsorption on polystyrene of PGM (Pig Gastric Mucin) and subsequent adhesion of L. lactis was performed for IBB477 and MG1820 strains. Measuring simultaneously shifts in resonance frequency and dissipation on the polystyrene-coated crystal demonstrated a two-phase process for PGM adsorption. XPS analysis confirmed the presence of adsorbed mucin. The Voigt-based model was used to describe the QCM-D outputs. The predicted thickness of the PGM layer was consistent with the AFM experimental value. Adhesion of L. lactis to bare or PGM-coated polystyrene was then monitored, in combination with DAPI cell counting. Positive frequency shifts were caused by adhering bacteria. The presence of adsorbed PGM strongly reduced bacterial adhesion. However, adhesion of IBB477 to the PGM coating was greatly increased in comparison with that of MG1820. Muco-adhesion may be a highly variable and valuable phenotypic trait among L. lactis strains. [ABSTRACT FROM PUBLISHER]

A normal power-law distribution of local resistivity with a uniform dielectric constant was found to be consistent with the constant-phase element (CPE). An analytic expression, based on the power-law resistivity distribution, was found that relates CPE parameters to the physical properties of a film. This expression worked well for such diverse systems as aluminum oxides, oxides on stainless steel, and human skin. Good values for film thickness were obtained, even when previously proposed expressions could not be used or yielded incorrect results. The power-law model yields a CPE impedance behavior in an appropriate frequency range, defined by two characteristic frequencies. Ideal capacitive behavior is seen above the upper characteristic frequency and below the lower characteristic frequency. A symmetric CPE response between the characteristic frequencies can be obtained by adding a parallel resistive pathway. [ABSTRACT FROM AUTHOR]

Constant-phase element (CPE) behavior may be attributed to the distribution of physical properties in films, in the direction normal to the electrode surface. Numerical simulations were used to show that under assumption that the dielectric constant is independent of position, a normal power-law distribution of local resistivity is consistent with the CPE. An analytic expression for the impedance corresponding to a power-law distribution of resistivity was developed and used to establish a relationship between parameters for the CPE and physical properties of the film. The resulting impedance response was compared to that obtained from the Young resistivity distribution. [ABSTRACT FROM AUTHOR]

A detailed analysis from both numerical calculations and experimental results is presented for the local electrochemical impedance spectroscopy (LETS) measurements of a disk electrode, which accounted for the placement of the LEIS probe above the electrode surface. The calculations for an electrode with a local constant phase element behavior were in excellent agreement with experimental observations for a stainless steel electrode in a Na2SO4/NaCl (pH 4) electrolyte. Measurement of the local impedance at two positions above the electrode surface allowed estimations of the local interfacial impedance and the local ohmic impedance, which were in excellent agreement with the simulations. The results demonstrate that the local impedance measurement itself cannot be used to estimate the surface area sampled by the LETS probe. The area sampled must be determined instead by the probe geometry. [ABSTRACT FROM AUTHOR]

Numerical methods were used to calculate the influence of geometry-induced current and potential distributions on the impedance response of a blocking disk electrode with a local constant-phase element behavior. While the calculated global impedance is purely capacitive, the local impedance has high-frequency inductive loops that were observed in experiments conducted on a stainless steel electrode in 0.05 M NaCI + 0.005 M Na2SO4 electrolyte. The calculated global impedance responses are in good agreement with experimental results obtained using both the steel electrode and a glassy-carbon disk in KCI electrolytes of differing concentrations. The computed local and both local and global ohmic impedances are shown to provide insight into the frequency dispersion associated with the geometry of disk electrodes. [ABSTRACT FROM AUTHOR]

Copper alloys, often used in cooling circuits of industrial plants using seawater as coolant, can be affected by biocorrosion induced by biofilm formation. Extracellular polymeric substances (EPS) produced by bacteria play a fundamental role in the different stages of biofilm formation, maturation and maintenance. The influence of loosely bound (LB) and tightly bound (TB) EPS, extracted from marine Pseudomonas NCIMB 2021, on the electrochemical behaviour of 70Cu–30Ni (wt.%) alloy in static artificial seawater (ASW) and on the chemical composition of oxide layers was studied by combined electrochemical measurements (polarization curves, EIS) and surface analysis (XPS, ToF-SIMS). Results were compared with those obtained in the presence of bovine serum albumin (BSA), a model protein. Compared to 70Cu–30Ni alloy in static ASW without biomolecules, for which a thick duplex oxide layer (outer redeposited Cu 2 O layer and inner oxidized nickel layer) is shown, the presence of BSA, TB EPS and LB EPS leads to a mixed oxide layer (oxidized copper and nickel) with a lower thickness. In the biomolecules-containing solutions, this oxide layer is covered by an adsorbed organic layer, mainly composed of proteins. A model is proposed to analyse impedance data obtained at the corrosion potential. The fitting procedure of impedance diagrams allows extracting the anodic charge transfer resistance, from which the corrosion current density can be calculated. The results show a slow-down of the anodic reaction in the presence of biomolecules (BSA, TB EPS and LB EPS), and a corrosion inhibition effect by LB EPS and to a lesser extent by BSA. No detrimental effect is evidenced with TB EPS. [ABSTRACT FROM AUTHOR]

Electrochemical methods (cyclic voltammetry (CV), potential steps, and electrochemical impedance spectroscopy) were successfully combined with in situ reflectometry measurements for a detailed analysis of the passive layer evolution as a function of the electrode potential. Interestingly, both EIS and surface reflectivity allowed a film thickness in the nanometer range to be readily determined. In addition, transient analyses of the reflectivity simultaneously recorded with CVs show the formation of both Fe 2 O 3 and Fe 3 O 4 oxides. The image analysis showed that the steel surface reactivity is heterogeneous and presents micrometric islands coated with a thicker oxide layer than the surrounding surface. The in situ combination of these techniques thus offers a powerful analytical description of the interface on a local scale and its transient response to a perturbation.

The objective of this paper is to study the corrosion resistance of orthodontic wires made of different alloys (stainless steel, chrome-cobalt, nickel-titanium and β-titanium) and for the same alloy from different vendors (GAC(®), RMO(®), 3M(®) and ORMCO(®)). Different electrochemical techniques (corrosion potential monitoring as a function of immersion time, current-potential curves, electrochemical impedance spectroscopy (EIS)) were used. The wires' resistance to corrosion was measured and compared with the surface condition, assessed by scanning electron microscopy (SEM). Using the recorded data, a rating system based on the corrosion resistance of orthodontic wires was developed. The comparison of these data with the results of SEM shows that the surface chemical composition plays a primary role in the electrochemical behavior of the orthodontic wires and, unlike surface defects, is a key parameter for the corrosion resistance of the alloy., (© EDP Sciences, SFODF, 2013.)