Surface free energies high-energy surfaces

Siloxanes have been widely used for many years as surfactants because of their high surface energy and activity as well as their stability towards heat, chemicals and UV radiation. The specific surface free energy of siloxanes (surface tension of -21 mN/m) is significantly lower than that of most hydrocarbons, which means that they will not only be positively adsorbed at hydrocarbon surfaces, but also that siloxanes lower the surface tension of their solutions (7). This property makes siloxanes very useful as surfactants. 

As a result of the high surface free energy of water, the vapor pressure of a water droplet increases with decreasing radius of curvature, r, as deduced by Kelvin ... 

A large surface area of the dispersed particles is associated with a high surface free energy that renders the system thermodynamically unstable. The surface free energy, AG, can be calculated from the total surface area, A A, as follows ... 

Very small dispersed particles are highly energetic. In order to approach a stable state, they tend to regroup themselves in order to reduce the surface free energy of the system. An equilibrium will be reached when AG = 0. This condition may be accomplished either by a reduction of the interfacial tension or by a decrease of the total surface area. 

IVa represents a physical bond resulting from highly localized intermolecular dispersion forces. It is equal to the sum of the surface free energies of the liquid, 7, and the solid, 72. loss the interfacial free energy, 7,2. It follows that Eq. (2.1) can be related to a model of a liquid drop on a solid shown in Fig. 2.2. Resolution of forces in the horizontal direction at the point A where the three phases are in contact yields Young s equation... 

The most important physical property of the solid that will affect solubility is particle size. For crystals < 1 pm, the high surface area may increase solubility. This occurs because it is the surface properties, especially the surface free energy, rather than the properties of the bulk solid, that govern the dissolution behaviour. Because the surface free energies of iron oxides are relatively high, particle size will have a marked... 

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