Spreading pressure interfacial tension

For the preparation of Langmuir monolayers, a detour is required, except when such layers can be made from Gibbs monolayers, by changing the composition of the substrate after adsorption hcis taken place, for example by changing the pH. The need for a detour is typical and requires some form of spreading. By this technique the amount of molecules at the interface is known and the interfacial tension or pressure are basicalty measurable. Hence, Jt[A] curves are obtainable. 

In the case of adsorbed layers, by analogy with the two-dimensional pressure of spread films, a surface pressure (n) is introduced defined as the change of - interfacial tension (y) caused by the addition of a given species to a base solution. At constant cell potential (E) this is... 

Non-equilibrium liquid films formed in the process of spreading have been considered in some early works, especially in the test of the theory of interfacial tension and the rule of Antonov [204], A review on the rule of Antonov and its interpretation on the basis of isotherms of disjoining pressure in wetting films is presented in [532]. However, these works do not deal with precise measurement of film thickness and the studies confined only the kinetics of spreading and lens formation. 

The interfacial (excess) heat capacity is another Interfacial characteristic that we decided to disregard. The reason for doing so is not in its intrinsic interest. On the contrary, as with bulk heat capacities, they reflect the structure, or ordering (see e.g. FIGS I, sec. 5.3c). However, it is very difficult to establish these values experimentally. Basically the second derivative of the interfacial tension with respect to the temperature at a constant pressure is needed (see sec. 1.2.7), and to obtain this extremely preeise measurements are needed. The spread in the quadratic coefficient B in [1.12.1) indicates the uncertainty, even for a well-studied liquid like water. Yang and Li showed, by a thermodyncimic ancdysis, that for LL interfaces this heat capacity is related to the two bulk heat capacities, the inter-... 

The third correction is due to changes in shape of the interface caused by the capillary. As the tube enters the aluminum, an interfacial tension force is formed along the outer edge of the tube. The resulting interfacial tension force is spread evenly over the cross section of the crucible leading to a pressure change of Txjr lr. ... 

FIGURE 10.24 Contact angles (6) of liquids at an A-S surface (upper row) and at an A-W surface (lower row). The pictures of the drops are cross sections through the largest diameter. A is air, L is liquid, O is oil, S is solid, W is water (or an aqueous solution). Numbers are interfacial tensions (y) in mN m-1.17S is spreading pressure. The scale varies among the panels. 

Generally, wastewaters are complex mixtures of solutes, which require theoretical approaches to predict multicomponent adsorption equilibria flxtm pure component adsorption data. The Ideal Adsorbed Solution model (IAS) was first established for a mixed gas adsorption by Myers and Prausnitz [9], and then extended to a multi-solute adsorption from dilute liquid solution by Radke and Prausnitz [10]. The model is based on the fundamental hypothesis that the multicomponent solution has the same spreading pressure s as that of the ideal single solution of the i component, the spreading pressure being the difference between the interfacial tension of the pure solvent and that of the solution containing the solute. This hypothesis is described by the Gibbs equation ... 

RELATION OF INTIAL SPREADING PRESSURE OF POLAR COMPOUNDS ON WATER TO INTERFACIAL TENSION, WORK OF ADHESION, AND SOLUBILITY. 

In order to understand the different effects of lipids on gas cell stability (Figure 7.10), we need to digress momentarily to focus on the properties of monomolecular films or monolayers. Monolayers may be studied by the use of a surface film balance, also called a Langmuir trough. When a compound is spread or adsorbs at an interface, it generally lowers the interfacial tension. The change in interfacial or surface tension (y) in the case of an air-aqueous interface is called the surface pressure (II) and is defined by... 

In the absence of surfactant species the interfacial tension will be constant (i.e., yCA ) = Y(A2) = Y> say). Therefore, y can be calculated directly from the pressure jump using equation (4). These values are compared in Table 1 with directly measured interfacial tensions. It can be seen that the values agree generally to within a spread of 0.5m Nm for each of the separate techniques. No differences could be detected between the AP values corresponding to narrowing and widening flows. 

Interfacial tension between a liquid and a solid. Eq. (25) applies to the contact between a liquid and a solid. If the subscripts 1 and 2 are replaced by L and S for liquid and solid, and it is combined with Eq. (14) with the spreading pressure set at zero, then Eq. (26) is the outcome. 

The key property we can measure of relevance to solid interfaces is the contact angle which, for smooth surfaces, can be related to the surface tensions of the liquid and solid and the solid-liquid interfacial tension via the Young equation. For rough surfaces we need to account for the roughness factor which can be obtained, for example, by atomic force microscopy experiments. For high energy surfaces, the solid-vapour surface tension should be corrected for adsorption phenomena (spreading pressure). 

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