Interfacial tension surface energies

Interfacial tension Surface energy Toughness in blends... 

Harkins WD, Davies ECH, Clark GL. The orientation of molecules in the surfaces of liquids, the energy relations at surfaces, solubility, adsorption, emulsification, molecular association, and the effect of acids and bases on interfacial tension. (Surface energy VI.) J Am Chem Soc 1917 39 541-596. 

The nucleation process has been discussed above in terms of the so-called classical theories stemming from the thermodynamic approach of Gibbs and Volmer, with the modifications of Becker, Doring and later workers. The main criticism of these theories is their dependence on the interfacial tension (surface energy), 7, e.g. in the Gibbs-Thomson equation, and this term is probably meaningless when applied to clusters of near critical nucleus size. 

Related articles are Contact angles and interfacial tension, Surface Energy and Wetting and spreading. 

In Figure 6.7, different interfacial tensions or energies of metals are correlated with the fusion temperature in the form 7 fus-Vrm. In general the ratio of the average surface energy of the solid to the surface tension of the liquid is around 1.2... 

Surfactants assist wetting because they lower surface and interfacial tension. The energy balance that determines spreading is expressed by the spreading coefficient, S, and is illustrated in Figure 6.21. 

Surface-active agents (surfactants) are substances which, at low concentrations, adsorb onto the surfaces or interfaces of a system and alter the surface or interfacial free energy and the surface or interfacial tension. Surface-active agents have a characteristic structure, possessing both polar (hydrophilic) and non-polar (hydrophobic) regions in the same molecule. Thus surfactants are said to be amphipathic in nature. The wide range of uses for surfactants in pharmaceutical products and systems is the subject of this article. 

Surface and Interfacial Tension Surface and interfaciai Free Energy... 

Related articles are Contact angles and interfacial tension. Surface characterization by contact angles - polymers. Surface characterization by contact angles - metals. Surface energy and Wetting kinetics. 

The pressure difference, AP, between the two fluid phases that causes capillary rise is a function of the interfacial tension (surface free energy) and the mutually perpendicular radii of curvature, ri and r2, for the interface between the two fluids. The pressure difference is known as the capillary pressure. Pc, and is defined as the pressure in the oil phase, Pq, less the pressure in the water phase, Pw If the porous medium is regarded as a bundle of capillaries with an average radius, r, equation 5 can be expressed as... 

Reported theories explain the stability of microemrd-sions. The driving force for the formation of stable microemrd-sions with a droplet structure is the entropy of dispersion of one liquid (oil, for instance) in the other (water). The presence of the cosurfactant is required for lowering the surface tension to a value low enough (0.01 mN/m) for the stabilization of the system. At such a low value of interfacial tension, the energy of the curvature of the surfactant layer must be taken into account in the calculation of the free energy of the system. In the case of bicontinuous microemrdsions, theory shows that a stable middle phase occurs when the average spontaneous curvature of the mixed surfactant + cosurfactant monolayer is close to zero and its bending modulus is close to 1 7 A unified treatment was recently reported. 

We sometimes use the term surface tension for hquids or solids in contact with air (or vacuum) and the term interfacial tension when we have two condensed phases in contact, e.g. hquid-hquid or hquid-solid. Nowadays, both terms are used, with the term interfacial tension or energy being the more rigorous one. 

Figure III-l depicts a hypothetical system consisting of some liquid that fills a box having a sliding cover the material of the cover is such that the interfacial tension between it and the liquid is zero. If the cover is slid back so as to uncover an amount of surface dJl, the work required to do so will he ydSl. This is reversible work at constant pressure and temperature and thus gives the increase in free energy of the system (see Section XVII-12 for a more detailed discussion of the thermodynamics of surfaces).

As it stands, eqn. (7.7) contains too many unknowns. But there is one additional piece of information that we can use. The interfacial energies, Ysl> Yes 7cl ct as surface tensions in just the way that a soap film has both a surface energy and a surface tension. This means that the mechanical equilibrium around the edge of the nucleus can be described by the triangle of forces... 

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