Composition dependence of surface

Since the surface tension is a thermodynamic property, one of the main problems is to define the surface tension of the ideal solution. The first attempt to define the behavior of the ideal solution was made by introducing the simple additivity law based on the molar fraction scale. However, such a behavior was never observed in real systems and several sophisticated attempts were therefore made to describe the composition dependence of surface tension in binary systems with sufficient accuracy taking into account the properties of both the components. Most approaches are based on the substitution of molar fractions by the volume fractions. Such an approach seems not to be quite reliable because of the energetics and not because of the volume character of this quantity. 

Relative surface activities of proteins go some way towards explaining the composition dependence of surface viscosity for films... 

The first term in braces represents the surface energy. With Eq. (8.24) we employ bulk PVT properties for evaluation of surface tension. Application of Eq. (8.24) to copolymers also allows for discussion of the composition dependence of surface tension. Patterson and Rastogi [1970] and Slow and Patterson [1971] published a similar approach in terms of the Flory, Orwoll, and Vrij equation of state. 

Limiting case n describes the composition dependence of surface tension observed for EVAc. The quantity y" " In fc = kpvac — Kpe = —0.4, which hints at 1. We selected fc=0.98, which implies that k" " = 19.8 mN/m. One may estimate the X-ratio in bulk using... 

The composition dependence of surface tension of a random copolymer was already discussed in Figure 2 of Paragraph 9.2. This copolymer showed negative deviation from linearity with respect to compositioa... 

Wu S (1982) Polymer Interface and Adhesion Marcel Dekker, New York, pp. 88-92. Kasemura T, Yamashita N, Suzuki K, Hondo T and Hata T (1978) Studies on surface tension of polymers in relation to their structures. IV. Composition dependence of surface tension of copolymers, Kobunshi Ronbunshu 35 263-268. 

Liquid alloys of Hg with a variety of metals (amalgams) constitute particularly complex systems in view of the potential dependence of surface composition. A detailed study of In and T1 amalgams, with... 

The degree of coverage, however, seems to influence the adsorbate composition at low methanol concentrations also. In particular, on smooth platinum, the dependence of surface composition on 6 is observed at concentrations as low as 5x 10-3 M (Fig. 2.7). In this case it could be possible that COH can be formed as long as adjacent sites are available. At high coverage (by all species involved in the adsorption process), the formation of COH should be geometerically prevented. 

Figure 9. Surface composition dependency of the Na - Co ( ) and K - Co ( ) selectivlties at 45 °C In zeolite Y. Reproduced with permission from Ref. 117. Copyright 1980, The Chemical Society.

By using a thermodynamic model based on the formation of self-associates, as proposed by Singh and Sommer (1992), Akinlade and Awe (2006) studied the composition dependence of the bulk and surface properties of some liquid alloys (Tl-Ga at 700°C, Cd-Zn at 627°C). Positive deviations of the mixing properties from ideal solution behaviour were explained and the degree of phase separation was computed both for bulk alloys and for the surface. 

Let us assume that the direct participation of dissolved oxygen in the reaction is insignificant. As a simplifying assumption, we will not take into consideration the dependence of surface reaction parameters on the composition of catalyst bulk the data about these dependences are still limited in number. 

One of the most intriguing aspects of surface diffusion is the strong dependence of the diffusivity on sorbate concentration. The dependence of surface diffusivities on pressure, temperature and composition is much more complicated than those of the molecular and Knudsen diffusivities, because of all the complexities of porous medium geometry, surface structure, adsorption equilibrium, mobility of adsorbed molecules, etc. 

The oxidation of soot in fuel-rich premixed flames proceeds through hydroxyl attack, with one atom of carbon removed by each OH radical hitting the surface of the soot. The absolute level and composition dependence of the disappearance rate of soot show that OH is the important species. The oxidation was followed experimentally by laser light scattering from soot particles generated in one flame and passed directly into the gas supply of a larger hydrogen/air flame controlled at 1700-2200 K. 

Nature of the Surface Complexes. The constant capacitance model assumes an inner-sphere molecular structure for surface complexes formed in reactions like equation 5a or 7. But this structure does not manifest itself explicitly in the composition dependence of Kc everything molecular is buried in which is an adjustable parameter. This encapsulating characteristic of the model was revealed dramatically by Westall and Hohl (13), who showed that five different surface speciation models, ranging from the Gouy-Chapman theory to the surface complex approach, could fit proton adsorption data on AL O., equally well, despite their mutually contradictory underlying molecular hypotheses [see also Hayes et al. (19)]. They concluded that "... no model will yield an unambiguous description of adsorption. .. . To this conclusion one may add that no model should provide such a description,... 

Taking into account the dependency of 2 on composition, Eq. (6.29) can be integrated. However, any composition dependency of the surface adsorption must fulfill the following boundary conditions for X2 = 0 is 2 = 0, but for X2 = 1, 2 attains some non-zero value. Such properties fulfill well the general function... 

Several attempts were made to describe the course of the dependency of surface tension on composition in the binary and ternary systems. 

Applications. The following uses of contact angle were reported in the literature surface energy of different sizes for fibers, correlation between contact angle of fiber and interlaminar shear strength of composite, effect of surface treatment of fillers for paints, the matrix-filler adhesion parameter for PS filled with CaCO, dispersion stability of PEO-modified kaolin particles, determination of contact angle of carbon fibers and its dependence on treatment, wettability of fiber sur-... 

Figure 4 The composition dependence of Y, qY, 2 2 binary slag systems with (a) non-surface-...

Photocurrent spectroscopy is a useful tool for the determination of bandgapsof in semiconductor alloys (Hutton and Peter, 1993) or surface films on metals (Peter, 1980, 1987 and 1989 Campbell et al., 1992). Figure 12.7 illustrates the composition dependence of the photocurrent onset energy for a series of Gai cAl cAs alloy samples (Hutton and Peter, 1992). The relationship between bandgap and composition is known for this system, so photocurrent spectroscopy is a convenient tool for compos-... 

Equilibrium segregation and equilibrium adsorption at solid-gas interfaces have often been formally treated as identical phenomena since both obey the Gibbs adsorption theorem. However, Gibbs rigourous results are difficult to apply due to the lack of information about various parameters, especially the composition dependence of the surface tension ). Therefore, a number of alternative approachs, based on experimental results have been attempted to predict and explain surface segregation. 

---