Interface of two immiscible electrolyte solutions

Koryta, J. Electrolysis at the interface of two Immiscible Electrolyte Solutions and its Analytical Aspects, in Ion-Selective Electrodes. 3rd. Symposium held at Matrafured, Hungary 1980, ed. Pundor, E., Elsevier, Amsterdam—Oxford—New York 1981... 

The system of distinctions and terminology of the thermodynamic and electric potentials introduced by Lange is still very useful and recommended for describing all electrified phases and interphases. Therefore these potentials can be assigned to metal/solution (M/s), as well as the liquid/liquid boundaries created at the interfaces of two immiscible electrolyte solutions water (w) and an organic solvent (s). 

Le Hung presented a general theoretical approach for calculating the Galvani potential Ajyj at the interface of two immiscible electrolyte solutions, e.g., aqueous (w) and organic solvent (s) [25]. Le Hung s approach allows the calculation of when the initial concentration (Cj), activity coefficients (j/,) and standard energies of transfer of ions (AjG ) are known in both solutions. 

The voltammetry for ion transfer at an interface of two immiscible electrolyte solutions, VITIES, which is a powerful method for identifying the transferring ion and for determining the amount of ion transferred, must be helpful for the elucidation of the oscillation process [17 19]. The VITIES was also demonstrated to be useful for ion transport through a membrane, considering that the membrane transport of ions is composed of the ion transfers at two aqueous-membrane interfaces and the mass transfers and/or chemical reactions in three phases [2,20,21]. 

The electrical oscillations at the aqueous-organic interface or at membranes in the absence of any substances relative to the channel or gate were introduced. These oscillations might give some fundamental information on the electrical excitability in living organisms. Since the ion transfer at the aqueous-organic or aqueous-membrane interface and the interfacial adsorption are deeply concerned in the oscillation, it has been stressed that the voltammetry for the ion transfer at an interface of two immiscible electrolyte solutions is... 

Early in the 20th century the first electrochemical study at an ITIES (interface of two immiscible electrolyte solutions) on ion transfer across a water-phenol interface was reported by pioneers Nernst and Riesenfeld [1], However, it was about 70 years before the start of the many interesting electrochemical studies of ITIESs, which successfully continue today. 

Fig. 4.1 Structure of the electric double layer and electric potential distribution at (A) a metal-electrolyte solution interface, (B) a semiconductor-electrolyte solution interface and (C) an interface of two immiscible electrolyte solutions (ITIES) in the absence of specific adsorption. The region between the electrode and the outer Helmholtz plane (OHP, at the distance jc2 from the electrode) contains a layer of oriented solvent molecules while in the Verwey and Niessen model of ITIES (C) this layer is absent...

Maredek, V., Z. Samec, and J. Koryta, Electrochemical phenomena at the interface of two immiscible electrolyte solutions, Advances in Interfacial and Colloid Science, 29, 1 (1988). 

J. Koryta, Electrolysis at the interface of two immiscible electrolyte solutions,... 

From the basic parameters initial concentration of ions, their standard transfer potential, distribution coefficients for neutral components, equilibrium constants of reactions taking place in the system, volume of phases, and temperature, a unique general problem for the Galvani potential difference and distribution concentration of all components was established. A numerical solution to the problem with the help of computer program EXTRA.FIFIl provided a good means for quantitative investigation of the liquid-liquid interface. It is also useful for the study of liquid-liquid extraction, electroextraction, voltammetry at interface of two immiscible electrolyte solutions (ITIES) [15,18], liquid-liquid membrane ion-selective electrodes, biomembrane transport, and other fields of science and engineering. 

In this chapter, the fundamental feature of parallel transports of types I and II elucidated with the aid of voltammetry for ion transfer at the interface of two immiscible electrolyte solutions is introduced, and compared with that of perpendicular transport [6-9]. 

The voltammetry for the ion transfer at the interface of two immiscible electrolyte solutions, VITIES, is expected to offer much information available for analyzing the ion transfer at the aqueous/membrane interface [14,15], if the organic solution is regarded as the membrane. Transfer energies of ions at the aqueous/membrane interface and amounts of ions transferred can be evaluated precisely by VITIES. The kinetics of the ion transfer and the interfacial adsorption can also be investigated by this method. The present authors measured the relations between the membrane potential and the membrane current (the... 

The first important investigation of a liquid membrane and, at the same time, of the interface of two immiscible electrolyte solutions (ITIES) was carried out by Nemst and Riesenfeld [2] at the beginning of this century. They measured not only the electrical potential difference between both the phases but also the effect of current flow across ITIES. Their ITIES was represented by a boundary between an aqueous solution and a solution in an organic solvent. Their main interest was not, however, in the current-potential characteristics but mainly in the proportion of cations and anions carrying the charge across ITIES. On the basis of their theory they could measure experimentally the transport numbers in the organic phase. 

Investigations of the properties of polarizable interfaces of two immiscible electrolyte solutions, as well as of their double-layer structures and zero-charge potentials were undertaken in numerous works [61,145,148]. Samec et al. [149] on the basis of the pioneer works by Verwey and Niessen [96], as well as by Gross et al. [61], formulated a model of the double layer. In this model a layer of oriented solvent molecules (the inner layer) separates two diffuse layers of the Gouy-Chapman type. 

Scanning ion conductance microscopy was applied to investigate the interface of two immiscible electrolyte solutions (ITIES). Two opposing views describe interfacial structure one opinion is that solvent dipoles orient to form an ion-free compact layer contained in a molecularly sharp interface. The sharp interface is proposed to separate two back-to-back double layers. The opposite view suggests the interface is composed of a mixed solvent layer that ions of both phases can penetrate. To adequately examine the interface, a technique with high-resolution and small probe are desired. An SECM study performed by Bard and coworkers of a water/nitrobenzene... 

Koryta, J., L. Q. Hung, and A. Hofmanova, Biomembrane transport processes at the interface of two immiscible electrolyte solutions with an adsorbed phospholipid monolayer. StudBiophys, Nol. 90, (1982) p. 25. 

The energy of ions transfer can be estimated from potentiometric data for the interfaces of two immiscible electrolyte solutions (ITIES) [22]. Early data for water/octane are tabulated in ref. [8]. However, oil-type solvents forming ITIES are not so common in usual nonaqueous electrochemistry. The specific details of the estimation of LJPs for completely and partly miscible organic liquids can be found in ref. [23]. 

The geometry of real polymer membranes still induces some problems with quantitative application of model calculations, and calibration procedure remains more or less empiric. However, the model systems imitating membranes, the interfaces of two immiscible electrolyte solutions (ITIES), are free from this shortcoming. Various types of LJP behavior for ITIES dependent on the ratios of ion partition coefficients are considered in ref. [95] remarks in ref. [96] are also useful. The effect of initial concentration distribution on the temporal LJP behavior is considered in ref. [97] self-consistently for the limiting cases of thick membranes (assumed to operate as ion-selective electrodes) and thin membranes (assumed to imitate biological membranes). 

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