Interfacial potential differences phase potentials, physics

An interfacial potential difference generally develops on contact between two immiscible liquid phases. The physical origin of this potential was the... 

Sometimes it is useful to break the inner potential into two components called the outer (or Volta) potential, if/, and the surface potential, x- Thus, (f) = if/ + x- There is a large, detailed literature on the establishment, the meaning, and the measurement of interfacial potential differences and their components. See references 23-26. Although silver chloride is a separate phase, it does not contribute to the cell potential, because it does not physically separate silver from the electrolyte. In fact, it need not even be present one merely requires a solution saturated in silver chloride to measure the same cell potential. 

Recent theoretical studies indicate that thermal fluctuation of a liquid/ liquid interface plays important roles in chemical/physical properties of the surface [34-39], Thermal fluctuation of a liquid surface is characterized by the wavelength of a capillary wave (A). For a macroscopic flat liquid/liquid interface with the total length of the interface of /, capillary waves with various A < / are allowed, while in the case of a droplet, A should be smaller than 2nr (Figure 1) [40], Therefore, surface phenomena should depend on the droplet size. Besides, a pressure (AP) or chemical potential difference (An) between the droplet and surrounding solution phase increases with decreasing r as predicted by the Young-Laplace equation AP = 2y/r, where y is an interfacial tension [33], These discussions indicate clearly that characteristic behavior of chemical/physical processes in droplet/solution systems is elucidated only by direct measurements of individual droplets. 

Quantum phenomena at the vacuum interface have been postulated in analogy with known effects at physico-chemical interfaces. To be consistent, special properties of the latter are therefore implied. A physical interface is the boundary surface that separates two phases in contact. These phases could be two solid phases, two liquid phases, solid-liquid, solid-gas or liquid-gas phases. What they all have in common is a potential difference between the two bulk phases. In order to establish equilibrium at the interface it is necessary that rearrangement occurs on both sides of the interface over a narrow region. Chemical effects within the interfacial zone are unique and responsible for the importance of surfaces in chemical systems. At the most fundamental level the special properties of surfaces relate to the difference between isolated elementary entities and the same entities in a bulk medium, or condensed phase. 

Various parameters are considered when selecting a reactor for chemical reactions, such as the number of phases involved, the differences in the physical properties of the participating phases, the post-reaction separation, the inherent reaction nature (stoichiometry of reactants, the intrinsic reaction rate, isothermal/adiabatic conditions, etc.), the residence time required, and the mass and heat transfer characteristics of the reactor. For a given reaction system, the first four aspects are usually controlled only to a limited extent if at all, while the remaining serve as design variables to optimize reactor performance. High rates of heat and mass transfer improve effective rates and selecti-vities and the elimination of transport resistances. This enables the reaction to achieve its chemicaT potential in the optimal temperature and concentration window. Transport processes can be ameliorated by increasing interfacial surface areas and short diffusion paths. These are easily attained in micro-stmctured reactors. 

Furthermore, as shown in Fig. 9.3, there arises between the two phases a difference in the outer potential Aipm - zpt — ip2, which is equivalent to what in physics called the contact potential. In electrochemistry we may call Arj>m the interfacial outer potential. The relation of Afj) to AipIJ2 is given by Eq. 9.6 ... 

Quantitative and (hopefully, at least) qualitative considerations are helpful in characterizing a liquid-liquid system for a potential extraction application. Batch shakeout tests are frequently the easiest way to determine basic feasibility by simply measuring the primary and secondary break times and by analyses to measure the compositions of the equilibrated phases. Such tests are readily conducted by mixing small volumes of each phase in a vial, which is then vigorously agitated and placed on a lab bench to settle. The resulting behavior of the liquid-liquid mixture depends on physical properties and system characteristics. The greater the density difference and interfacial tension between the two liquid phases, for example, the more rapidly the phases tend to separate. More viscous systems separate more slowly. 

How to go beyond this intrinsic HNC problem In the absence of the moment of improved integral equations (with some bridge functions in the conventional approach or with new, non-conventional ones), one is forced to use the standard procedure and impose reasonable constraints for the ions at will. Figure 11 illustrates what happens to the ionic distributions when the very same potential for water is offered to the ions as well (in a sense, this bubble-ion potential could be identified with the negative of the bridge function ). In this way, by construction, ions stay inside the liquid phase. The corresponding air-ion effective potentials are given in Fig. 11. With the same surface-particle potential, the more physical NaCl system of Fig. 6 exhibits quite a different interfacial property despite the soft repulsion imposed on all ions, the chloride ions prefer now to stay at the interface, just on top of water. To what extent does this... 

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