Interfacial zone

Measurements [113,368] of interfacial (contact) potentials or calculated values of the relative work functions of reactant and of solid decomposition product under conditions expected to apply during pyrolysis have been correlated with rates of reaction by Zakharov et al. [369]. There are reservations about this approach, however, since the magnitudes of work functions of substances have been shown to vary with structure and particle size especially high values have been reported for amorphous compounds [370,371]. Kabanov [351] estimates that the electrical field in the interfacial zone of contact between reactant and decomposition product may be of the order of 104 106 V cm 1. This is sufficient to bring about decomposition. [Pg.33]

Whether they are called surfaces or interfaces, when the zones between parts of a structure are "thin"— from a fraction of a micrometer (the limit of the ordinary microscope) down to molecular dimensions—the matter in them assumes a character that is somewhat different from that seen when the same matter is in bulk form. This special character of a molecular population arranged as an interfacial zone is manifested in such phenomena as surface tension, surface electronic states, surface reactivity, and the ubiquitous phenomena of surface adsorption and segregation. And the stmcturing of multiple interfaces may be so fine that no part of the resulting material has properties characteristic of any bulk material the whole is exclusively made up of transition zones of one kind or another. [Pg.168]

According to Frumkin and Damaskin, A% at the air/solution interface changes linearly with composition, i.e., the interface behaves as two condensers in series. "" On a molecular basis, this model is tantamount to assuming that an adsorbate and solvent do not interact in the interfacial zone, but create two homogeneous surface layers. [Pg.39]

Usually g-J(ion) 7 Aj I and J(dip) / Aj/. This is caused by mutual influence of the contacting phases on the orientation of dipolar molecules in the interfacial zone. [Pg.20]

It should be emphasized that the ester carbonyl group in the interfacial zone II is most crucial and susceptible to the anesthetic action of the drugs. In our NMR study, we have found that the ester carbonyl site in zone II is particularly susceptible to the extent of hydration [51]. Above the G/LC transition temperature, the carbonyl is the innermost site where the water can penetrate. The strong perturbation of the NMR signal of the... [Pg.791]

The aliphatic tails form a hydrocarbon region with properties not too different from the hydrocarbon core of bilayers. The clusters have an interfacial zone... [Pg.19]

Ionizable molecules embedded in the surfaces of lipids, such as octanol (see Fig. 2.8), liposomes (see Fig. 5.2), or micelles, will have their apparent pKa values shifted. With neutral lipids, the pKa of an acid increases and the pKa of a base decreases. This is due to the effect of the decreased dielectric constant in the interfacial zone, as we have already discussed in various sections. [Pg.86]

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). [Pg.271]

Interfacial tension studies are particularly important because they can provide useful information on the interfacial concentration of the extractant. The simultaneous hydrophobic-hydrophilic nature of extracting reagents has the resulting effect of maximizing the reagent affinity for the interfacial zone, at which both the hydrophobic and hydrophilic parts of the molecules can minimize their free energy of solution. Moreover, as previously mentioned, a preferential orientation of the extractant groups takes place at the interface. Conse-... [Pg.224]

Relationship Between Nodular and Rejecting Layers. Nodular formation was conceived by Maler and Scheuerman (14) and was shown to exist in the skin structure of anisotropic cellulose acetate membranes by Schultz and Asunmaa ( ), who ion etched the skin to discover an assembly of close-packed, 188 A in diameter spheres. Resting (15) has identified this kind of micellar structure in dry cellulose ester reverse osmosis membranes, and Panar, et al. (16) has identified their existence in the polyamide derivatives. Our work has shown that nodules exist in most polymeric membranes cast into a nonsolvent bath, where gelation at the interface is caused by initial depletion of solvent, as shown in Case B, which follows restricted Inward contraction of the interfacial zone. This leads to a dispersed phase of micelles within a continuous phase (designated as "polymer-poor phase") composed of a mixture of solvents, coagulant, and a dissolved fraction of the polymer. The formation of such a skin is delineated in the scheme shown in Figure 11. [Pg.278]

The essential step is the efficient grinding and blending of raw materials. The final properties of cement strongly depend on its mineral composition so that raw composition and firing conditions are adjusted, depending on the type of cement to be produced. The microstructure of the steel fiber-cement paste interface was studied by scanning electron microscopy (SEM). The interfacial zone surrounding the fiber was found to be substantially different from the bulk paste further away from the fiber surface. The interfacial zone consisted of... [Pg.220]

Outside this, a highly porous layer parallel to the interface. The interaction of cracks initiated in the matrix with this interfacial zone was observed. [Pg.220]

This alteration of the interphase by the addition of an epoxy rich layer caused a change in the fundamental material behavior of the interfacial zone and consequently caused significant changes in the composite behavior as well. [Pg.23]

Comparison of profundal diffusion rates with observed increases in the hypolimnion (Table III) indicated that pore-water diffusion calculated from these profiles was probably not an important transport mechanism for Hg in this seepage lake. For the June-July period, pore-water diffusion accounted for only 13% of the hypolimnetic increase. For the July-August interval, pore-water diffusion could account for only 7% of the observed increase. Therefore, we can assume that the buildup in the hypolimnion is more likely a result of redissolution of recently fallen particulate matter at the sediment surface than of direct pore-water diffusion. Our present sampling scheme (2-cm intervals) precludes evaluation of dissolution in the uppermost sediments and would require much more detail (<1 cm) in the sediment-water interfacial zone. [Pg.444]

To evaluate C](5 ) and C1(L ), we introduce what has been designated [28, 29] the interfacial zone equilibrium approximation the concentration profiles of all charged defect species within the two interfacial regions (0interior zone (5 local space-charge neutrality can be approximated by... [Pg.75]

To evaluate the rate coefficient in terms of the interfacial defect concentrations, it is thus necessary to evaluate Ci (8 ) and Ci (L ), utilizing one aspect of the interfacial zone equilibrium approximation. At thermal equilibrium... [Pg.77]

This result can be noted to depend upon the mobilities of both species and the boundary concentrations of these species at the interfaces of the oxide film. In contrast, the potential differences across zones 1 and 3 do not involve the mobilities, which is in accordance with the interfacial zone equilibrium approximation. [Pg.79]

An interesting example of a specific ion effect in microemulsions is a strong increase in reactivity found for large, polarizable anions such as iodide. The tendency for such ions to interact with, and accumulate at, the interface can be taken advantage of for preparative purposes. The increased concentration of such ions in the interfacial zone, where the reaction takes place, will lead to an increase in reaction rate. Expressed differently, the reactivity of iodide and other highly polarizable ions [62, 63] will be very high in such systems. The microemulsions need not be based on cationic surfactants that would drive the anions to the interface by electrostatic attraction. Also microemulsions based on nonionic surfactants display the effect because large, polarizable anions interact... [Pg.68]

Wu el al. (W33) and Monteiro and co-workers (M116,MI15) observed that, within the interfacial zone, the content of ettringite increases as the aggregate surface is approached. [Pg.378]

Interfaces of calcium aluminate cements with aggregates were discussed in Chapter 10. The interfacial zone between Portland cement paste and steel has been studied by SEM, using various techniques of specimen preparation (e.g. A31,B153). The major features observed have been substantial deposits of CH and, further away from the interface, a relatively weak, porous zone. Bentur ct al. (B135) also reported the occurrence of a duplex film. Interfaces of cement or CjS pastes with zinc (A32,T58) or copper (T58) have been studied. [Pg.382]

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. [Pg.250]

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