Interphase definition

Tray Efficiencies in Plate Absorbers and Strippers Compn-tations of the nnmber of theoretical plates N assnme that the hqnia on each plate is completely mixed and that the vapor leaving the plate is in eqnihbrinm with the liqnid. In actnal practice a condition of complete eqnihbrinm cannot exist since interphase mass transfer reqnires a finite driving-force difference. This leads to the definition of an overall plate efficiency... 

The performance of a product where adhesion plays a role is determined both by its adhesive and cohesive properties. In the case of silicones, the promotion of adhesion and cohesion follows different mechanisms [37]. In this context, adhesion promotion deals with the bonding of a silicone phase to the substrate and reinforcement of the interphase region formed at the silicone-substrate interphase. The thickness and clear definition of this interphase is not well known, and in fact depends on many parameters including the surface physico-chemistry of... 

At any interface between two different phases there will be a redistribution of charge in each phase at the interface with a consequent loss of its electroneutrality, although the interface as a whole remains electrically neutral. (Bockris considers an interface to be sharp and definite to within an atomic layer, whereas an interphase is less sharply defined and may extend from at least two molecular diameters to tens of thousands of nanometres the interphase may be regarded as the region between the two phases in which the properties have not yet reached those of the bulk of either phase .) In the simplest case the interface between a metal and a solution could be visualised as a line of excess electrons at the surface of the metal and an equal number of positive charges in the solution that are in contact with the metal (Fig. 20.2). Thus although each phase has an excess charge the interface as a whole is electrically neutral. 

More commonly used is another definition of Gibbs surface excesses, according to which r, is equal to the amount of substance j that must be added to the system (with a constant amount of the substance j = 0) so that the composition of the bulk phases will remain unchanged when the interface area is increased by unity. This definition can also be used when chemical reactions take place in the surface layer. In the case discussed here, the two definitions coincide. The set of surface excesses of all components is sometimes called the surface phase (in contrast to the real surface layer or interphase). 

Because of this formation, a different definition of the enthalpy must be introduced for the interphase, differing from the usual expression for a homogeneous phase ... 

The interfacial zone is by definition the region between the crystallite basal surface and the beginning of isotropy. Due to the conformationally diffuse nature of this region, quantitative contents of the interphase are most often determined by indirect measures. For example, they have been computed as a balance from one of the sum of the fractional contents of pure crystalline and amorphous regions. The analysis of the internal modes region of the Raman spectrum of polyethylene, as detailed in the previous section of this chapter, was used to quantify the content of the interphase region (ab). 

This definition requires some explanation. (1) By interface we denote those regions of the two adjoining phases whose properties differ significantly from those of the bulk. These interfacial regions can be quite extended, particularly in those cases where a metal or semiconducting electrode is covered by a thin film. Sometimes the term interphase is used to indicate the spatial extention. (2) It would have been more natural to restrict the definition to the interface between an electronic and an ionic conductor only, and, indeed, this is generally what we mean by the term electrochemical interface. However, the study of the interface between two immiscible electrolyte solutions is so similar that it is natural to include it under the scope of electrochemistry. 

Liquid chromatography (LC) and, in particular, high performance liquid chromatography (HPLC), is at present the most popular and widely used separation procedure based on a quasi-equilibrium -type of molecular distribution between two phases. Officially, LC is defined as a physical method... in which the components to be separated are distributed between two phases, one of which is stationary (stationary phase) while the other (the mobile phase) moves in a definite direction [ 1 ]. In other words, all chromatographic methods have one thing in common and that is the dynamic separation of a substance mixture in a flow system. Since the interphase molecular distribution of the respective substances is the main condition of the separation layer functionality in this method, chromatography can be considered as an excellent model of other methods based on similar distributions and carried out at dynamic conditions. 

The concept sounds attractive, but there is a flaw in the explanation. Assuming an equilibrium situation between the two bulk phases and the interphase, complex formation at the interfacial region requires the same complexes are formed also in the bulk phases. Consequently, in order to produce a considerable amount of the mixed species MA, xBx in the liquid-liquid boundary layer some B must be dissolved in the aqueous, as weU as some A in the organic phase. Since by definition this condition is not met, the relative amount of M present at the interphase region as MAn xBx must be negligible. However, now the metal ion will be distributed between MA in the aqueous phase and MBp in the organic layer (n and p are the... 

Chemical reaction states, reactivity of states, 1467 Chemical reaction, as a basic step. 937. 1473 adiabatic, definition, 1497 at gas/solid interphase, 1371 heterogeneous, in solution. 1376 non-adiabatic, definition, 1497 reactivity of molecules in, 1473 velocity of. 1473... 

Interfacial electrochemistry is about electric charges at interfaces between phases, one of which is an electron conductor and the other an ion conductor. The kinetic part of the subject is about the rate at which these charges transfer across the interphase. However, this definition clearly embraces two limiting cases. 

Geckeler, K. E., Rupp, F., and Geis-Gerstorfer, J. 1997. Interfaces and interphases of (bio(materials Definitions, structures, and dynamics. Advanced Materials 9 513-18. 

This article has attempted to put spillover in perspective. At this time, there seem to be more questions than definitive conclusions. As with any newly discovered phenomenon, spillover has been used to explain a variety of phenomena on heterogeneous solids. Even if limited to interphase phenomena the picture is clouded. The influence is well documented, but the extent of the relative influence has been studied in less quantitative terms. Further, it... 

Another useful thermodynamic relationship that allows the potential dependence of l to be determined from the differential capacity Co, of the interphase at constant rs is readily obtained from the very definition of l. Choosing Ez as the reference potential and denoting by lz the electrosorption valency at Ez, the l value at any other applied potential E is given by ... 

We have seen that there is no ambiguity in the thermodynamic definition of the NHE scale. A detailed analysis, in terms of the various A(t) values at different interphases in the cell, is less straightforward. At first we might be tempted to assign a zero value to the metal-solution potential difference at the normal hydrogen electrode... 

The surface excess T represents the total amount of the relevant species in a cylinder of unit cross section, extending from the interface into the bulk of the solution, less the amount that would have been in the same volume, had there been no interface. Fortunately, we do not have to determine how far exactly the interphase extends. The function (C - C ) is integrated to "infinity" - far enough into the bulk that its value has become negligible. It should be noted that on the scale of interest for interphases, "infinity" is not very far. In fact, it is less than 1 xm For the example just discussed, ( )(1 pm) = ( ) exp(—100). The definition of the surface excess is shown graphically in Fig. IH. 

The formation of 2D Meads phases on a foreign substrate, S, in the underpotential range can be well described considering the substrate-electrolyte interface as an ideally polarizable electrode as shown in Section 8.2. In this case, only sorption processes of electrolyte constituents, but no Faradaic redox reactions or Me-S alloy formation processes are allowed to occur, The electrochemical double layer at the interface can be thermodynamically considered as a separate interphase [3.54, 3.212, 3.213]. This interphase comprises regions of the substrate and of the electrolyte with gradients of intensive system parameters such as chemical potentials of ions and electrons, electric potentials, etc., and contains all adsorbates and all surface energy. Furthermore, it is assumed that the chemical potential //Meads is a definite function of the Meads surface concentration, F, and the electrode potential, E, at constant temperature and pressure Meads (7", ). Such a model system can only be... 

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