Bulk phase, definition

During the experiments conducted up to this point, it was, therefore, not possible to give the solid bulk phase definite forms. Still, it could be shown by the experiments illustrated in Fig. 5 that the rate of reaction depended on the size of the solid phase which was here varied between 0.1 and 2.0 g. 

A third definition of surface mobility is essentially a rheological one it represents the extension to films of the criteria we use for bulk phases and, of course, it is the basis for distinguishing states of films on liquid substrates. Thus as discussed in Chapter IV, solid films should be ordered and should show elastic and yield point behavior liquid films should be coherent and show viscous flow gaseous films should be in rapid equilibrium with all parts of the surface. 

It has been shown (16) that a stable foam possesses both a high surface dilatational viscosity and elasticity. In principle, defoamers should reduce these properties. Ideally a spread duplex film, one thick enough to have two definite surfaces enclosing a bulk phase, should eliminate dilatational effects because the surface tension of an iasoluble, one-component layer does not depend on its thickness. This effect has been verified (17). SiUcone antifoams reduce both the surface dilatational elasticity and viscosity of cmde oils as iUustrated ia Table 2 (17). The PDMS materials are Dow Coming Ltd. polydimethylsiloxane fluids, SK 3556 is a Th. Goldschmidt Ltd. siUcone oil, and FC 740 is a 3M Co. Ltd. fluorocarbon profoaming surfactant. 

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). 

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... 

If we assume above / = 1 excess fluorine atoms over those required to fill the available surface are in a bulk solid phase of definite composition, then the second moment of the line is the weighted sum of the second moments of fluorine in the bulk phase ((AH ))b and fluorine on the filled surface That is, if n, is the mole fraction on the filled surface and... 

Apart from the fact that the layer is very thin and that its vapour pressure is equal to that of the wet lens, no definite information is available on this point. On the other hand, in the case of ethyl alcohol, acetic and the lower fatty acids, we have noted already that a tightly packed unimolecular layer is readily obtained long before the vapour pressure above the solution is equal to that of the pure alcohol (since Fmax. is obtained in this case at 0 3 molar) or acid. Thus for these substances to obtain equality of vapour pressure between a surface and bulk phase, layers more than one molecule thick must be necessary. 

In a second step, the former Gibbs definition of the interface (Equation D3.5.I), which explicitly contains the inner energies of the bulk phases a and (3, gives ... 

Adsorbed films between two immiscible liquids. The question of the meaning of the term pn in the surface layer has been raised by Crax-ford, Gatty, and Teorell,2 without, however, coming to any very clear decision. Danielli s estimate was a very rough one, based on the application of the Donnan equilibrium between the surface layer and the interior, and suffers from the difficulties always attending an attempt to consider concentrations in the surface layer in a similar way to concentrations in a bulk phase the surface layer is not homogeneous. pH is closely related to, and is determined by, the electrochemical potential (see Chap. VIII, pp. 304 ff.), and this depends on the electrostatic potential, which varies rapidly at different levels near to the surface it appears possible that the only satisfactory definition of pa in the surface may be one which varies rapidly at different depths. The question appears one which would repay... 

The definition applies only to a symmetrical film, for which the two bulk phases on either side of the film are the same, and y is the surface tension of a film/bulk interface. 

In the above discussed examples definite film thickness. Quite obvious there arises the question as to how reliable could be their extrapolation to the surface of the bulk phase. Studies of (po(h) dependence with thick films has indicated that thickness affects weakly the potential so the extrapolation to h — °° is reasonable. 

The membrane in a broad sense is a thin layer that separates two distinctively different phases, i.e., gas/gas, gas/liquid, or liquid/liquid. No characteristic requirement, such as polymer, solid, etc., applies to the nature of materials that function as a membrane. A liquid or a dynamically formed interface could also function as a membrane. Although the selective transport through a membrane is an important feature of membranes, it is not necessarily included in the broad definition of the membrane. The overall transport characteristics of a membrane depends on both the transport characteristics of the bulk phase of membrane and the interfacial characteristics between the bulk phase and the contacting phase or phases, including the concentration polarization at the interface. The term membrane is preferentially used for high-throughput membranes, and membranes with very low throughput are often expressed by the term barrier. ... 

It has been mentioned already that the exchange of kink atoms with the ambient phase can be used for the definition of the equilibrium. This statement is based on the fact that the separation of kink atoms requires the same Gibbs energy as the average disintegration energy per atom of an infinitely large crystal, which is related to the chemical potential of the atoms in the bulk phase. 

The driving force is usually defined as a concentration difference between the interface and the bulk phase. For gases, however, it is more common to use the pressure difference as the driving force. We can thus formulate two different definitions of the mass transfer flux, and then derive an expression for the relation between the concentration based and the pressure based mass transfer coefficients. 

The membrane of Stuchebrukchov s model is an infinite surface, where the multitude of proton binding sites (carboxylates with pK = 5) is represented by a density function (cr). The dwell time of a proton on any of the sites is determined by the pK (Tdweii = l disfeon), but dufing this time interval the proton can diffuse on the surface with a diffusion coefficient that is 10% of the bulk value (Dg 0.1 Db), screening an area with a radius Lg. On the surface, there is a proton-channel acting either as an absorbing sink, or a source which affects the immediate proton concentration, both at the surface and in the solution. The bulk phase in this model is an infinite reservoir, which is sufficiently far from the proton-consuming cluster to satisfy the demand AC/Ax = 0, a definition that is based on a chemical function... 

Surface chemists, who are used to these sorts of problems, have defined a quantity called the surface excess, a measure of surface concentration per unit area which can be related to macroscopic, measurable thermodynamic variables such as the change in interfacial tension. The surface excess, denoted P, of a soluble surfactant is defined as the excess amount per unit area present in a finite section through the surface (i.e., including some of each phase) compared to the amount that would be present in an identical section of the aqueous bulk phase containing the same number of moles of water as the surface section. It can be shown that such a definition implies the existence of a plane such that the excess of water present in the fuzzy air phase above is balanced by the depleted amount of water in the fuzzy water phase below. The surface excess of the water is thus taken as zero. If this plane is taken as the zero of a depth scale into the bulk solution and c(x) is the profile of concentration of a surface-adsorbed species, it can be shown that ... 

Orientation (Chapter 5) refers to the preferred positioning of parts or groups of molecules in the bulk phase without the establishment of long-range order. Crystallinity (Chapter 5) presupposes not only a three-dimensional preferential arrangement of the chains, but also definite interrelationships between the lattice points. The chain atoms, with their substituents, can be considered as lattice points. Thus, with polymers, in contrast to low-molecular-mass chemistry, it is not the mutual arrangement of the lattice points of various molecules which must be considered, but also the arrangement of the lattice points of an individual macromolecule relative to the other lattice points of the same molecule. 

On the other hand. X-ray diffraction (XRD) measurements of the deposited platinum films (ca. 250 ML) on the Au(lll) substrate demonstrated that a (lll)-orientated platinum-bulk phase was definitely formed on the Au(lll) electrode surface by electrochemical epitaxial growth [32]. 

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