Study on ferrocene derivatives diffusion dynamics in polymer electrolyte by solid-state voltammetry

The diffusion rates of seven ferrocene derivatives have been estimated in polyelectrolyte PEG . LiClO4 by using non-steady-state chronoamperometry. The D-app of ferrocene derivatives increases with temperature, and the dependency of D-app on temperature obeys the Arrhenius equation. The D-app of ferrocene derivatives decreases with increasing size of electroactive species. The Delta D-app values of D-T>Tm and D-Tdiffusion species. The dependency of D-app on the size of ferrocene at T < T-m is larger than that at T > T-m in the polyelectrolyte. On the other hand, the diffusion behaviour of ferrocene derivatives is qualitatively analyzed by using cyclic voltammetry. Copyright (C) 1996 Elsevier Science Ltd

A study of the dependence of ferrocene diffusion on electrolyte concentration and size in a polymer medium using non-steady-state chronoamperometry

This article describes a quantitative study of the diffusion rate of ferrocene(Fc) dissolved in ploy(ethylene glycol)(PEG) medium containing MClO(4)(M = Li+, Na+, Bu(4)N(+), Hx(4)N(+)). The apparent diffusion coefficient D-app and the active concentration c(a) of Fc were simultaneously measured by using non-steady-state chronoamperometry. The D-app and c(a) of Fc have been estimated in PEG containing different concentrations and sizes of supporting electrolyte, and the dependence of D-app on ferrocene concentrations has been observed. The values of D-app decrease with increasing concentrations of Fc, increasing concentrations of LiClO4 or the ratio (O:Li) and also with 4 decreasing cation radius of the electrolyte. The temperature dependencies conform to a simple free volume model. The concentration and size of the counterion dependencies of the diffusion rate are similar to the behavior of their dependencies of ionic conductivity in polyelectrolyte.

INFLUENCE ON THE THIN-LAYER SPECTROELECTROCHEMISTRY - DIFFUSION WITHIN A THIN-LAYER CELL

The potential step and cyclic voltammetric experiments in the thin layer cell were studied by the digital simulation method in this work. A relationship between the time needed for exhaustive electrolysis of the electroactive species and the thickness of the thin layer cell was obtained. On the basis of this formula, the lower time limit for a kinetic plot of the following chemical reaction can be estimated. For the cyclic voltammetry, a semiempirical formula was derived for the peak-peak potential difference (Delta Ep) in terms of the sweep rate (v), thickness of the cell (d), diffusion coefficient (D) and electron transfer number (n) 59 - n Delta Ep/n Delta Ep = 0.328(RT D/nF vd(2))(1.20).

UNSTEADY DIFFUSION KINETICS OF ZIEGLER-NATTA HETEROGENEOUS CATALYST POLYMERIZATION .4. PREDICTION OF EXPERIMENTAL RESULTS OF PROPYLENE ETHYLENE 1-HEXADECENE TERPOLYMERIZATION

The prediction, based on unsteady diffusion kinetics, of the enhancement of reactivity and incorporation of 1-hexadecene in its copolymerization with propylene on adding a small amount of ethylene (increase from 5,2 mol-% to 10,8 mol-% when 2% of ethylene was added, and to 16,1 mol-% when 5% was added) was verified in the terpolymerization of propylene/1-hexadecene/ethylene on a commercial Solvay-type delta-TiCl3 catalyst. The catalyst efficiency was thus also increased. These augmentations originate from the increase in diffusion coefficient of 1-hexadecene at the catalyst surface when the PP crystallinity decreases on introduction of ethylene. Calculation based on unsteady diffusion kinetics showed that the order of diffusion coefficients ethylene > propylene > 1-hexadecene is reversed as the monomer concentration increases when the monomers are not at their equilibrium concentration. Sequence distribution as determined by means of C-13 NMR revealed a tendency of blocky structure rather than a Bernoullian one. The terpolymer compositions obtained by means of an IR method developed in this work conform rather well with the NMR results. Results in this work not only support the unsteady diffusion kinetics but also provide a new route to prepare olefinic copolymer rubbers with heterogeneous titanium catalysts.

CHRONOAMPEROMETRIC STUDIES ON MIGRATION AND DIFFUSION OF COUNTERION IN POLY(3-METHYLTHIOPHENE)

Small amplitude potential step experiments were carried out to study the counterion transfer process in oxidized poly(3-methylthiophene) (PMT) film. The results demonstrate that anion transfer process in PMT film is migration rather than diffusion. A porous metal electrode model-single hole model, which takes into account both the ionic resistance of the film and the uncompensated solution resistance, was found suitable to describe the potential step experiments. According to this model, the ionic resistivity of oxidized PMT film was calculated to be 5.0 x 10(4) OMEGA.cm, and, in turn, the diffusion coefficent of ClO4- ion in PMT film 3.7 x 10(-9) cm2/s.

STUDY ON MEASUREMENT OF DIFFUSION-COEFFICIENT OF LI ATOM IN LIQUID ALUMINUM

The tess potential-concentration curve was first applied to measure the concentration of an alloy. Attempt to use the V-c curve of Al-Li alloy in measuring the diffusion coeffictent of Li atom in liquid aluminium with anode chronopotentiometry at 720℃, was made and D_(Li/Al=4.94×10~(-5)cm~2·s~(-1) was obtained. The value is well consistent wish the theoretical value, D_(Li/Al)=4.85×10~(-5)cm~2·s~(-1) in terms of Stokes-Einstein equation.

Effects of organic modifiers on solute retention and electrokinetic migrations in micellar electrokinetic capillary chromatography

Influences of seven organic modifiers, including urea, methanol (MeOH), dioxane (DIO), tetrahydrofuran (THF), acetonitrile (ACN), 1-propanol (1-PrOH) and 2-propanol (2-PrOH), on the solute retention and the electrokinetic migrations in micellar electrokinetic capillary chromatography (MEKC) are investigated with sodium dodecyl sulfate (SDS) micelle as pseudostationary phase. It is observed that in the limited concentration ranges used in the MEKC systems the effect of organic modifier concentration on the retention can be described by the equation logk'=logk'(w)-SC for most binary aqueous-organic buffer, but deviations from this retention equation are observed at ACN and particularly THF as organic modifiers. With parameter S as a measure of the elutropic strength, the elutropic strength of the organic modifiers is found to follow a general order urea

Characteristics of elution profile in radial chromatography under linear conditions

Based on the mass balance equations of solute transfer in the radial chromatographic column, the theoretical expression to describe the column efficiency and shape of elution profile is obtained under linear isotherm case. Moreover, the tendency for the variation of column efficiency and symmetry of peak profile is systematically discussed. The results showed that in radial chromatography the relationship between the column efficiency and volumetric flow rate is similar with that relationship in axial chromatography; relatively high column efficiency still can be obtained under high flow rate in radial chromatography. Accompanying the increase of retention factor of solutes and injection time, the column efficiency decreases monotonously. The effect of column diameter and column length on the column efficiency interfere with each other. It is more advantageous to increase the column efficiency by applying columns with larger column diameter and shorter column length. According to the discussion of the effect of diffusion on the column efficiency, radial chromatography is proved to be suitable for the separation of samples with relatively high diffusion coefficient, which predicts its obvious advantage in the preparative separation of samples such as proteins and DNA.