Interphase border

When matter passes through an interphase border, e.g., through a liquid -phase border, the matter evaporates and takes up thermal energy. 

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According to data /3/, the AE sources in the fibrous composites are plastic deformation and cracking of the die material, shift stratification on the fibre-die interphase border, fibre destmction and stretching fibres out of the die. 

If the vessel contains both liquid and gas, then the additivity will no longer hold in general, but is, if at all, restricted to carefully selected regions. In particular, it must be probed along an interphase border, in a certain position to catch equal amounts of the phases and surface. 

In accordance with equilibrium thermodynamics, at constant pressure in a one-component system phase transition occurs at a sp>ecific temperature and it should be accompanied by a sudden change in heat release or absorption, i.e. phase transition has no extension in time or hysteresis. It should be noted, that although interphase border is an integral part of any system where phase transition takes place, classical equilibrium thermodynamics does not pay any attention to the possible contribution of this border to phase transitions. 

One of the most interesting and perspective directions in material engineering of the last years is development of technology of nano-materials consisting from two or more phases with precise interphase border and nanostructured materials based on interpenetrated polymer network. Nowadays many countries are leaders in nanotechnology not only in fundamental academic researches but mainly in industrial introduction of scientific and technological achievements. Some important results in the nano-materials engineering are sununarized in this chapter. 

As is known, composite materials are two- or multi-phase with well-defined interphase border. Such materials contain the reinforcing elements immersed into a polymeric, ceramic or metal matrix. Mechanical properties of composites depend on structure and properties of the interphase border. Phases of usual composite materials have micron and submicron sizes. 

For the following discussion, the definitions of adsorption and surface layers are introduced. The thin surface layers of any condensed phase have different structrue and physical properties as compared with the properties in bulk, and their thickness does not exceed the radius of correlation of structural long range interaction. These layers can be considered as interphase layers. Any liquid or solid body has an interphase layer. This interphase (border or surface) layer may be qualified as a layer in which, under the action of the surface force field, properties differ from those in bulk. The surface layer has an effective thickness beyond which the deviations of local properties from bulk are neghgi-ble. ... 

Actions of the superficial interphase phenomena of wetting, spreading, and adhesions on a border of oligomer filler... 

From the early 1980s, it was well accepted that the desired performance of a polymer-based heterogeneous material would pass through a well-optimized interaction level across the interphases between the components (4). The interphase is defined as the dynamic and finite spatial region placed between the border of each of the two different phases where momentum, mass, and energy transport phenomena may occur. 

If the chemical reaction is fast compared to the mass transfer of the gaseous reactant A from the gas phase into the liquid phase, the reaction in the liquid film has to be considered. In the border case of an instantaneous reaction, the reactants are converted in a reaction plane located in the liquid film or even directly at the gas-liquid interphase. For illustration, we limit ourselves to a first-order reaction with respect to the gaseous reactant A, for example, we may have a pseudo-first-order reaction if the liquid reactant B is in excess (negligible gradient of B). Initially, we also assume that the mass transfer resistance in the gas film can be neglected (Figure 4.4.4). The equation of the steady state two-film theory then leads to ... 

Studying adsorption from solution of polymer mixtimes is of great interest for the theory of PCM because many binders for composites are two-and more-component systems. The presence of two components determines the specificity of the properties of the boundary layers formed by two different polymeric molecules. From another point of view, as the large majority of polymer pairs is thermodynamically immiscible,there may arise interphase layers between two components in the border layer at the interface. The selectivity of adsorption of various components, which is a typical feature of adsorption from mixture, leads to the change in composition of the border layer as compared with composition in the equilibrium solution. This fact, in turn, determines the non-homogeneity in distribution of components in the direction normal to the solid surface, i.e., creates some compositional profile. As compared with stud3ung adsorption from solution of individual polymers, adsorption from mixture is studied insufficiently. The first investigations in this field were done " for immiscible pair PS-PMMA on silica surface, in conditions remote from the phase separation. It... 

From the analysis presented above, it becomes pertinent that when a polymer is in contact with a solid having higher surface tension, the increase in the surface tension of a polymer will be observed due to polarization. It is also evident that the value Wc should be considered as a cohesion energy of the interphase region but not of pol5mier in bulk. This value may or may not coincide with the cohesion energy of polymer far from the phase border. The same conclusion follows from the analysis of an interaction between sohd and hquid along... 

Concluding the thermodynamic analysis, we would like to note that all the approaches are based on the general principles of thermodynamics and they do not account for specific features of pol3oner behavior used to explain properties of polymer solutions, adsorption, mechanical properties, etc. We believe that the science of adhesion should be transformed from general and qualitative descriptions to the quantitative analysis of the interphase phenomena based on statistical theories. It is also desirable to distinguish between adhesion at various phase borders such as non-polymeric solid-polymer, polymeric adhesive-an-other polymer (in any phase or aggregate state). 

The discussion presented above allows one to formulate a model representation of the structure of the border layer of polymer alloys near the interface and of the filled polymer alloy. We accept that the border layer consists simultaneously of both polymers, each interacting with the sohd independently. In the binary mixture near the interface, as in the matrix bulk, there exists an interphase region between the two immiscible polymers (Figure 7.12). The interaction between components in this interphase region is characterized by the parameter Xab, which serves as a measure of miscibility. The experimental data allows one to conclude that the conditions for various chain interactions are not the same as in the matrix bulk. As a result, the experimental values ofxAB for the interphase... 

It is weU known that a passivation layer, called the solid-electrolyte interphase (SEI), forms on the surface of the negative electrode (and likely on the positive electrode to some extent as well) due to reaction with the electrolyte (see Chapter 1). This layer will add a resistance for reaction to occur. The exact nature of the SEI is not weU understood. There is evidence that the film on the carbon and lithium electrodes is inhomogeneous, possibly porous, composed of more-reduced species (c.g. lisCOg) on the side bordering the active material and less-reduced species e.g. lithium alkyl-carbonates) on the side bordering the electrolyte. A model of transport and reaction in the SEI layer could be based on previous works on passivation layers formed in other systems, e.g., corrosion of iron [66,671, or it could expand upon models of the LiCl layer in lithium-thionyl chloride batteries [68,69]. 

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