Interfacial discontinuity

Such smoothing of the threshold between polarities within the interfacial discontinuity surface is possible when the polarity of the introduced third component is intermediate with respect to those of two other components, that make up the phases in contact. The smoothing is especially effective, when it is achieved via the adsorption of diphilic molecules containing segments with different polarities. These molecules are the organic surfactants that can smoothen the difference in polarity between water and any solid or liquid hydrocarbon phase ( further referred to as oil ). When the adsorption takes place, the polar heads of the surfactant molecules are oriented towards water, while the hydrocarbon chains face the oil phase (Fig. III-5). As... 

The physical dimensions of the interfacial discontinuities appear to be such that they cannot be detected by visible optics, nor have first attempts to show their existence by capacitance measurements been fruitful. Thus far it has been necessary to rely on data which support the proposition but do not provide unequivocal evidence that incomplete "wetting is primarily responsible for the observed performance. An example is the "activation energy" of the bonding process. This has... 

Virtually all practical systems should exhibit complete wetting at equilibrium. In practice, however, interfacial equilibrium is frequently not achieved. Under these circumstances high stress concentration at the interfacial discontinuities leads to poor performance. The stress concentration is determined by the viscoelastic response of the adhesive and the time-temperature characteristics of the test used to assess the performance. 

Summarizing IR NEA surfaces, we find that 1) the height of the interfacial discontinuity, rather than X of the surface layer, is the true limit to high IR efficiency 2) although photoemitters in this general class are all called NEA, those which push the low-energy limit of the concept are not truly NEA but are actually small-positive-affinity devices and 3) there is a bit of rivalry and uncertainty present in the NEA field (cf. [5.12, 69]). 

If the primary currents lie in several conductivity compartments, then each wiU yield a term similar to the first integral in Equation 20.21.) Note that in Equation 20.20 and Equation 20.21 the secondary source field is similar in form to the field in a homogeneous medium of infinite extent, except that ap is piecewise constant and consequently introduces interfacial discontinuities. With regard to the potential, these just cancel the discontinuity introduced by the double layer itself so that i is appropriately continuous across each passive interface. 

An interesting question that arises is what happens when a thick adsorbed film (such as reported at for various liquids on glass [144] and for water on pyrolytic carbon [135]) is layered over with bulk liquid. That is, if the solid is immersed in the liquid adsorbate, is the same distinct and relatively thick interfacial film still present, forming some kind of discontinuity or interface with bulk liquid, or is there now a smooth gradation in properties from the surface to the bulk region This type of question seems not to have been studied, although the answer should be of importance in fluid flow problems and in formulating better models for adsorption phenomena from solution (see Section XI-1). 

Fig. 14—Interfacial slip revealed by the velocity profile from simulations of confine liquid decane the step in the profile at location f indicating a velocity discontinuity between the wall and the molecules adjacent to the wall [26].

Opinions differ on the nature of the metal-adsorbed anion bond for specific adsorption. In all probability, a covalent bond similar to that formed in salts of the given ion with the cation of the electrode metal is not formed. The behaviour of sulphide ions on an ideal polarized mercury electrode provides evidence for this conclusion. Sulphide ions are adsorbed far more strongly than halide ions. The electrocapillary quantities (interfacial tension, differential capacity) change discontinuously at the potential at which HgS is formed. Thus, the bond of specifically adsorbed sulphide to mercury is different in nature from that in the HgS salt. Some authors have suggested that specific adsorption is a result of partial charge transfer between the adsorbed ions and the electrode. 

As both phases occupy the full flow field concurrently, two sets of conservation equations correspond to these two phases and must be complemented by the set of interfacial jump conditions (discontinuities). A further topological law, relating the void fraction, a, to the phase variables, was needed to compensate for the loss of information due to model simplification (Boure, 1976). One assumption that is often used is the equality of the mean pressures of the two phases, ... 

Nakato, Y., Yano, H., Nishiura, S., Ueda, T., and Tsubomura, H., Hydrogen photoevolution at p-type silicon electrodes coated with discontinuous metal layers, ]. Electroanal. Chem. Interfacial Electrochem., 228,97,1987. 

Saturation (v) is the volume fraction of the total void volume occupied by a specific fluid at a point. Saturation values can vary from zero to 1 with the saturation of all fluids equal to 1. Residual saturation (Sr) is the saturation at which the NAPL becomes discontinuous and immobile due to capillary forces. Residual saturation is dependent upon many factors, including pore size distribution, wettability, fluid viscosity and density ratios, interfacial surface tension, gravity and buoyancy forces, and hydraulic gradients. 

The value of /jim is determined by the discontinuity in the dependence of cell current on applied cell voltage which occurs when the interfacial concentration approaches zero. The polarisation parameter is convenient in the design and scale-up of electrodialysis equipment. It can be easily measured in small-scale stacks at a given value of bulk concentration and then used to predict limiting current densities in larger stacks at other concentrations. Most stacks use operating values of the polarisation parameter that are 50-70 per cent of the limiting values. 

The interface between two fluids is in reality a thin layer, typically a few molecular dimensions thick. The thickness is not well defined since physical properties vary continuously from the values of one bulk phase to that of the other. In practice, however, the interface is generally treated as if it were infinitesimally thin, i.e., as if there were a sharp discontinuity between two bulk phases (LI). Of special importance is the surface or interfacial tension, a, which is best viewed as the surface free energy per unit area at constant temperature. Many workers have used other properties, such as surface viscosity (see Chapter 3) to describe the interface. 

The relationships between the overall mass transfer coefficient and the film mass transfer coefficients in both phases are not as simple as in the case of heat transfer, for the following reason. Unlike the temperature distribution curves in heat transfer between two phases, the concentration curves of the diffusing component in the two phases are discontinuous at the interface. The relationship between the interfacial concentrations in the two phases depends on the solubility of the diffusing component. Incidentally, it is known that there exists no resistance to mass transfer at the interface, except when a surface-active substance accumulates at the interface to give additional mass transfer resistance. 

A discontinuous precipitate often was observed at citrus oil/ aqueous phase interfaces kept at 50 C for prolonged periods. The precipitate particles congregate on the water side of the citrus oil/aqueous phase interface and disperse into the aqueous phase upon agitation. If the aqueous phase is distilled water, or a supernatant phase, the precipitate particles cause the aqueous phase to become noticeably cloudy. Precipitate particles or interfacial films were not detected at citrus oil/complex coacervate phase interfaces. However, such interfaces normally were not kept for prolonged periods, because their IFT values rapidly decayed to a value too low to measure. 

These assumptions are continuity of stress and velocity across the interfaces since stress discontinuities owing to high interfacial tensions increase the viscosity (3), to explain the unexpected low viscosities we must doubt the validity of the velocity condition at the interfaces. This is supported by the fact that the two polymers are incompatible, which implies a relatively low concentration or even complete absence of entanglements at the interface. A very thin layer of solute-free solvent around the droplets would result. Such a low viscosity layer might be the cause of the anomalous behavior. 

Many studies of vulcanized elastomer blends have revealed discontinuities in physical property trends attributable to poor interfacial bonding. Recently Rehner and Wei (5) have observed discontinuities in the swelling of blended crosslinked networks swollen in a common solvent. This departure from an averaged swelling behavior, based upon compositional ratios and the swelling behavior of the two homophases, re-... 

SBM) as a compatibilizer. As a result of the particular thermodynamic interaction between the relevant blocks and the blend components, a discontinuous and nanoscale distribution of the elastomer at the interface, the so-called raspberry morphology, is observed (Fig. 15). Similar morphologies have also been observed when using triblock terpolymers with hydrogenated middle blocks (polystyrene-W<9ck-poly(ethylene-C0-butylene)-Wock-poly(methyl methacrylate), SEBM). It is this discontinuous interfacial coverage by the elastomer as compared to a continuous layer which allows one to minimize the loss in modulus and to ensure toughening of the PPE/SAN blend [69],... 

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