Interfacial transfer kinetics

The interfacial transfer kinetics were then investigated by perturbing the equilibrium, through the depletion of Cu + in the aqueous phase, by reduction to Cu at an UME located in close proximity to the aqueous-organic interface. This process promoted the transfer of Cu into the aqueous phase, via the transport and decomplexation of the cupric ion-oxime complex, resulting in an enhanced steady-state current at the UME. Approach curve measurements of i/i oo) vs. d allowed the kinetics of the transfer process to be determined unambiguously [9,18]. 

Byron and coworkers [7,8] developed and evaluated a transport cell which proved to be useful in predicting interfacial transfer kinetics between aqueous and organic boundary layers. In this system, stirring is generated by using paddles in each phase. These investigators demonstrated that successful prediction of the transfer kinetics of any homologue in a series was possible in all cases from... 

P Byron, M Rathbone. Prediction of interfacial transfer kinetics. I. Relative importance of diffusional resistance in aqueous and organic boundary layers in two-phase transfer cell. Int J Pharm 21 107, 1984. 

At surfactant concentrations near the CMC, an enhanced blocking of the surface and change in interfacial rheology, and thus reduction of mass transfer may occur [67]. However, even low surfactant concentrations with species of high adsorption affinity may show the similar effect. As to this, it is essential to know the adsorption behavior of single or mixed adsorption layers to properly predict their impact on interfacial transfer kinetics. 

Determination of the interfacial transfer kinetics of the charged or non-charged species... 

Qu W, Mudawar I (2002) Experimental and numerical study of pressure drop and heat transfer in a single-phase micro-channel heat sink. Int J Heat Mass Transfer 45 2549-2565 Qu W, Mudawar I (2004) Measurement and correlation of critical heat flux in two-phase micro-channel heat sinks. Int J Heat Mass Transfer 47 2045-2059 Ren L, Qu W, Li D (2001) Interfacial electro kinetic effects on liquid flow in micro-channels. Int J Heat Mass Transfer 44 3125-3134... 

The interpretation of phenomenological electron-transfer kinetics in terms of fundamental models based on transition state theory [1,3-6,10] has been hindered by our primitive understanding of the interfacial structure and potential distribution across ITIES. The structure of ITIES was initially studied by electrochemical and thermodynamic analyses, and more recently by computer simulations and interfacial spectroscopy. Classical electrochemical analysis based on differential capacitance and surface tension measurements has been extensively discussed in the literature [11-18]. The picture that emerged from... 

The theoretical results described have implications for the design of experimental approaches for the study of transfer processes across the interface between two immiscible phases. The current response in SECMIT is clearly sensitive to the relative diffusion coefficients and concentrations of a solute in the two phases and the kinetics of interfacial transfer over a wide range of values of these parameters. 

For comparable diffusion coefficients of the target solute in the two phases and nonlimiting transfer kinetics, systems characterized by different should be resolvable on the basis of transient and steady-state current responses to a value of up to 50 at practical tip-interface separations. If the diffusion coefficient in phase 2 becomes lower than that in phase 1, diffusion in phase 2 will be partly limiting at even higher values of K. On the other hand, as the value of y increases or interfacial kinetics become increasingly limiting, lower values of suffice for the constant-composition assumption for phase 2 to be valid. 

As the immunocomplex structure is generally electroinactive, its coverage on the electrode surface will decrease the double layer capacitance and retard the interfacial electron transfer kinetics of a redox probe present in the electrolyte solution. In this case, Ra can be expressed as the sum of the electron transfer resistance of the bare electrode CRbare) and that of the electrode immobilized with an immunocomplex (R immun) ... 

The electronic properties of CNTs, and especially their band structure, in terms of DOS, is very important for the interfacial electron transfer between a redox system in solution and the carbon electrode. There should be a correlation between the density of electronic states and electron-transfer reactivity. As expected, the electron-transfer kinetics is faster when there is a high density of electronic states with energy values in the range of donor and acceptor levels in the redox system [2]. Conventional metals (Pt, Au, etc.) have a large DOS in the electrochemical potential... 

Subscript (ads) denotes adsorption via a thiolate linkage, while (ps) stands for a physisorbed and/or adsorbed state via different interactions. However, large dimensions of the studied molecules and their amphiphilic nature make the surface reaction mechanism more complex than in case of cystine/cysteine. Interfacial microstructure plays an important role in the determination of the surface behavior of the adsorbed molecules. From the study on the charge-transfer kinetics, the transfer coefficient a was calculated as slightly less than 0.50, while the rate constant (based on Laviron s derivations [105]) was of the order of 10 s k The same authors [106] have shown earlier that the adsorption rate constant of porcine pancreatic phospholipase A2 at mercury via one of its disulfide groups is of the order of 10 s h... 

The heart of interfacial electrochemical kinetics is electron transfer—metal to solution and solution to metal. The electron is a particle, the movement and properties... 

Tafel s law is the primary law of electrode kinetics, in the sense that Arrhenius law is the basic law of thermal reaction. It applies universally to all processes that are controlled in rate by the interfacial transfer of electrons or by a rate-determining surface reaction that may be coupled to the interfacial electron [Fig. 9.25(a)]. Redox reactions without surface intermediates demonstrate Tafel s law well [Fig. 9.25(b)]. 

The assumption on the electric charge effect of excess electrons on the rate constant of their interfacial transfer is supported by an evident similarity of these semiconductor colloidal systems with metal colloids, for which effect of the charge of electrons captured by the particle is well known and agrees with the microelectrode theory . Moreover, kinetic curves similar to those we found for CdS colloids were observed previously for silver colloids in ref. [17], where the particles charge q was shown to decrease by the law... 

Thus, it may be seen that, by reducing the particle radius, it is possible to obtain systems where transit from the particle interior to the surface occurs more rapidly than recombination, implying that quantum efficiencies for photoredox reaction of near unity are feasible. However, the achieving of such high quantum efficiencies depends very much upon the rapid removal of one or both types of charge carrier upon their arrival at the semiconductor surface, underlining the importance of the interfacial charge-transfer kinetics. This is the subject of the next section. 

In the case of colloidal semiconductors whose interfacial charge transfer kinetics are consistent with those assumed during the derivation of equation (9.28), the rate of charge transfer from the particles to the charge carrier acceptor in solution is proportional to the surface area of the particles. Albery et al. assume that, within the systems that they studied, the particle radii conform to a Gaussian distribution. Thus, in analogy to equations (9.30) and (9.31) ... 

The overall permeation rate of a material is determined by both ambipolar conductivity in the bulk and interfacial exchange kinetics. For -> solid electrolytes where the electron - transference numbers are low (see -> electrolytic domain), the ambipolar diffusion and permeability are often limited by electronic transport. 

Characteristic potential — means the potential of a certain singular point in electrochemical response that is characteristic of the particular charge-transfer process (- charge-transfer kinetics) or interfacial phenomenon. Any characteristic p. is related to given experimental conditions (such as the temperature, the nature of the solvent, and supporting -> electrolyte and its concentration). The nature and type of characteristic p. depends on the technique that is employed. Typical characteristic potentials are the -> half-wave potential in -> po-larography and the -> peak potentials in -> voltammetry, similar maximum/minimum of inflection points can be listed for other techniques. 

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