Local Mass Transfer in Turbulent Flow by Electrochemical Methods

Mass transfer to the surface of rotating electrodes during turbulent flow was studied by electrochemical methods under steady and non-steady state diffusion conditions. The flow was due to a large rotating disk made from insulating material, flush with the surface of which was mounted a ring shaped electrode of platinum or nickel. A local study of the radial component of the convective diffusion in turbulent flow was carried out with very thin ring electrodes (width ΔR ~ 0,05 mm). The diffusion layer thickness was varied relatively to the diffusion sublayer thickness by changing the ring width or the rotation speed so as to determine the eddy diffusivity in the viscous sublayer. The local viscous friction was measured at the wall by a steady state method. As an application, the drag reduction phenomenon was studied in the presence of high polymer additives. Using a non-steady state method which yields the electrochemical impedance, we examined the possibility of adsorption of polymers at the wall- fluid interface

Interaction Model of the Interface Nasicon with Aqueous Solution

Complex impedance spectroscopy (CIS) study was carried out using the 4-electrodes cell arrangement with NASICON membrane. The physical model developed in this work was based on own CIS characteristic of the system NASICON/solution, and it accurately described the experimental diagrams. The electronic parameters could be determined from the fittings with the designed model

Electroacoustic Polymer Microchip as an Alternative to Quartz Crystal Microbalance for Biosensor Development

Laser photoablation of poly(ethylene terephthalate) (PET), a flexible dielectric organic polymer, was used to design an acoustic miniaturized DNA biosensor. The microchip device includes a 100-μm-thick PET layer, with two microband electrodes patterned in photoablated microchannels on one side and a depressed photoablated disk decorated by gold sputtered layer on the other side. Upon application of an electric signal between the two electrodes, an electroacoustic resonance phenomenon at ∼30 MHz was established through the microelectrodes/PET/ gold layer interface. The electroacoustic resonance response was fitted with a series RLC motional arm in parallel with a static C0 arm of a Buttlerworth-Van Dyke equivalent circuit: admittance spectra recorded after successive cycles of DNA hybridization on the gold surface showed reproducible changes on R, L, and C parameters. The same hybridizations runs were performed concomitantly on a 27-MHz (9 MHz, third overtone) quartz crystal microbalance in order to validate the PET device developed for bioanalysis applications. The electroacoustic PET device, ∼100 times smaller than a microbalance quartz crystal, is interesting for the large-scale integration of acoustic sensors in biochips

Electrochemical Oxidation Assessment and Interaction of 2-aminoethanol and N, N-diethylethanamine Propagation in Acidic Medium

Electro�oxidation and inhibitor performance of copper specimens in 1 M hydrochloric acid solu� tion was investigated at room temperature by linear potentiodynamic polarization and gravimetric method in the presence of 2�aminoethanol (A) and N, N�diethylethanamine (D) as an inorganic inhibitor. The effect of the inhibitory concentration on the corrosion behavior of copper was studied over 288 hrs at 298°K. The inhibitory efficiency rise up to 96% for single induced and 98% for synergistic behavior. The adsorption mechanism characteristic was supported by SEM/EDX analysis and adsorption isotherm. From all indica� tion, the inhibitive efficiency of these compounds majorly depends on their molecular structure and concen� tration. The blocking effects of the surface interface were also explained on the basis of the inhibitor active action. 2�aminoethanol and N, N�diethylethanamine inhibits copper in 1 M HCl by strictly affecting both the anodic and cathodic sites. Portion of the surface covered calculated was also found to follow Langmuir adsorption isotherm

Mass transfer in a laminar elongational flow of a drag reducing surfactant

The mass transfer given by an electrochemical reaction towards a rotating disk in a solution of surfactant having drag reducing abilities exhibits a first order transition. Beyond this transition marked by a significant slump of the mass transfer rate, the flow becomes unsteady and is characterised by an hysteresis cycle. This phenomenon was earlier observed for viscoelastic dilute solutions of linear polymers of high molecular weight and is induced by the elongational strain prevailing in the flow around a rotating disk. © 2002 Elsevier Science B.V. All rights reserve

Spectral analysis of hydrodynamic tracer dispersion with an electrochemical measurement technique

International audienceWe report tracer dispersion measurements in a capillary tube performed in the frequency domain using an electrochemical technique. Tracer Fe+++ ions are produced by oxidizing Fe++ ions at an emission anode; the inverse reaction allows to detect the tracer on a measurement electrode at the outlet of the sample. The amplitude and phase of the steady state signal detected at the outlet of the sample are measured as a function of the frequency of a sinusoidal concentration modulation induced at the inlet of the tube. Measurement results at two flow velocities are in agreement with predictions of the Taylor-Aris model

Transport de charges transitoire à travers des couches de polyaniline électropolymérisées sur platine, en présence d’un système redox en solution

La réduction de [math] et l’oxydation de [math] se déroulent sous contrôle diffusionnel sur une électrode modifiée par la polyaniline. Les courants limites de diffusion mesurés sur une électrode à disque tournant correspondent à ceux prévus par la relation de Levich. La modulation de la vitesse de rotation induit une modulation de courant qui contient à la fois la réponse du flux modulé du substrat à l’interface polymère/solution et de la charge et décharge de la capacité redox du polymère