Surface properties interphase thermodynamics

Although the thermodynamic description of an interphase is an invaluable tool, it is rarely used. The traditional approach of Gibbs requires the use of a dividing surface to which interfacial properties are referenced. This method is burdened with notational and conceptual difficulties [ 184]. As alternative but equivalent method of treating interphase thermodynamics was developed by Cahn [185], which avoided... 

The thickness of the interphase is a similarly intriguing and contradictory question. It depends on the type and strength of the interaction and values from 10 Ato several microns have been reported in the hterature for the most diverse systems [47,49,52,58-60]. Since interphase thickness is calculated or deduced indirectly from some measured quantities, it depends also on the method of determination. Table 3 presents some data for different particulate filled systems. The data indicate that interphase thicknesses determined from some mechanical properties are usually larger than those deduced from theoretical calculations or from extraction of filled polymers [49,52,59-63]. The data supply further proof for the adsorption of polymer molecules onto the filler surface and for the decreased mobility of the chains. Thermodynamic considerations and extraction experiments yield data which are not influenced by the extent of deformation. In mechanical measurements, however, deformation of the material takes place in all cases. The specimen is deformed even during the determination of modulus. With increasing deformations the role and effect of the immobilized chain ends increase and the determined interphase thickness also increases (see Table 3) [61]. 

Vaia and Giannelis [19] emphasized that the main fundamental aspects differentiating nanocomposites from conventional composites are their vast interfacial areas per unit volume and the nanoscopic dimensions between the nanoelements. The presence of many chains at interfaces means that much of the polymer is really interphase-like instead of having bulk-like properties. Furthermore, the polymer chains are quite often confined between the surfaces of nanoplatelets which are closer to each other than the radius of gyration of a chain. Both adjacency to a nanoplatelet surface and confinement between such surfaces clearly modify the thermodynamics of polymer chain conformations and the kinetics of chain motions. These two factors may potentially also modify the effective mechanical properties of the polymer. Such... 

The final category of surface modifications to be considered has its origins in the thermodynamics of interfaces and interphases within multi>component polymers and is therefore an inherent feature of such systems. It is, in a sense, beyond the control of the scientist or engineer involved. Inherent modifications are noted here in some detail because they are apt to be neglected in practise, and yet represent an important built-in source of variations in the performance of bonds, barrier and mechanical properties of polymer systems. 

A fundamental aspect of our MD treatment is its acceptance or assumption of the existence, in each surface parallel to the electrode, of local thermodynamic functions and variables and of thermodynamic properties for all species whose individual molecules or ions are centered in that surface. This assumption is equivalent to the statement that we consider only systems for which the Gibbs entropy-balance equation holds locally. In some regions of the interphase between the bulk of the metal and the bulk of... 

The single most important property of a polymeric interpheise is its interfacial tension. This property describes the energy required to create the interphase and can be readily defined through classical thermodynamics. The interfacial tension Y for a polymer-air interface (ie, the surface tension) is generally defined in terms of the work required to reversibly divide and separate a material into two parts, as depicted in Figure 1. The work required to perform the separation is called the work of cohesion, Wc, and provides an operational definition for the surface tension ... 

In order to use these equations it is necessary to devise a model which enables the surface excess concentration of species i in the interphase to be defined. The interphase itself is defined by enclosing it in two arbitrary planes positioned in such a way that the bulk phases extend homogeneously up to these planes. Any changes in the thermodynamic properties must occur between these planes (Fig. 5.3). If the thickness of the phase is known, then the concentration of species i can be mathematically expressed this is the Guggenheim model. An alternative approach due to Gibbs introduces a third arbitrary plane called the dividing surface which acts as a reference surface. The concentration of species i can then be expressed in terms of an excess or deficiency of component i at the reference surface with respect to its concentration in the bulk phase. 

Before approaching the problem of dynamics of contact line, we shall briefly review the equilibrium properties of gas-liquid interfaces and their dependence on the proximity to solid surfaces. We shall consider the simplest one-component system a liquid in equilibrium with its vapor. Thermodynamic equilibrium in a two-phase system implies equilibrium of the interphase boundary, which tends to minimize its area. The thermodynamic quantity that expresses additional energy carried by the interface is surface tension, defined as the derivative of the Helmholtz or Gibbs free energy with respect to interfacial area E ... 

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... 

It has been suggested that in practical non-aqueous lithium battery systems the anode (Li or graphite) is always covered by a surface layer named the solid electrolyte interphase (SEI), 1-3 run thick, which is instantly formed by the reaction of the metal with the electrolyte. This film, which acts as an interphase between the metal and the solution, has the properties of a solid electrolyte. This layer has a corrosive effect and grows with the cycling life of the battery [52], Thermodynamic stability of a lithium cell requires the electrochemical potentials of electrodes a and Ec located within the energetic window of the electrolyte, which contrains the cell voltage Eq of th electrochemical ceU to ... 

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