Surface free energy solids

The existence of the mesophase layer has been proved by infra-red spectroscopy, ESP, NMR, electron microscopy and other experimental methods. Moreover, it has been also proved that the thickness of this layer depends on the polymer cohesion energy, free surface energy of the solid, and on the flexibility of the polymer chains. 

When an adsorbing surface is exposed to a gas or vapour adsorption will take place, being accompanied by the absorption or evolution of heat. Such thermal changes have already been noted in the extension and contraction of surface films of liquids. Although the direct determination of the surface energy of solid surfaces presents many experimental difficulties yet of its existence there is no doubt. On the adsorption of a gas or vapour a diminution in the free surface energy of the system likewise occurs. From the Gibbs-Helmholtz relationship dcr... 

If there is a decrease in the free surface energy the liquid will continue to displace the gas from the surface of the solid, i.e. the solid will be wetted by the liquid if... 

The adsorption of various substances from solids is due to the increased free surface energy of the solids due to their extensive surface. According to the second law of thermodynamics, this energy has to be reduced. This is achieved by reducing the surface tension via the capture of extrinsic substances. 

Surface and Interfacial Tension. Some properties of liquid surfaces are suggestive of a skin that exercises a contracting force or tension parallel to the surface. Mathematical models based on this effect have been used in explanation of surface phenomena, such as capillary rise. The terms surface tension (gas—liquid or gas—solid interface) and interfacial tension (liquid—liquid or liquid—solid) relate to these models which do not reflect the actual behavior of molecules and ions at interfaces. Surface tension is the force per unit length required to create a new unit area of gas—liquid surface (mN/m (= dyn/cm)). It is numerically equal to the free-surface energy. Similady, interfacial tension is the force per unit length required to create a new unit area of liquid—liquid interface and is numerically equal to the interfacial free energy. 

Practical applications of surfactants usually involve some manner of surfactant adsorption on a solid surface. This adsorption is always associated with a decrease in free-surface energy, the magnitude of which must be determined indirectly. The force with which the adsorbate is held on the adsorbent may be roughly classified as physical, ionic, or chemical. Physical adsorption is a weak attraction caused primarily by van der Waals forces. Ionic adsorption occurs between charged sites on the substrate and oppositely charged surfactant ions, and is usually a strong attractive force. The term chemisorption is applied when the adsorbate is joined to the adsorbent by covalent bonds or forces of comparable strength. 

Rate of Solubility—The rath of solubility of small particles depends on a great number of variables. Eq (12-2) takes into account free surface energy (a) and particle surface (1 /d). These are purely surface considerations, and are scarcely complete in themselves. The shape of the surface and its physical state must also be specified, that is, its relative freedom from contamination which might influence the speed of reaction. The effect of packing density and the extent of agitation imparted to the particles are also important, particularly with regard to exposure of fresh surfaces and formation of possible gas pockets. The liquid and liquid-solid phases jointly are additional important considerations. The volume of the liquid, its temperature, and the amount of dissolved solid already in solution must enter into all calculations. Nor can we ignore the chemical nature of the substances involved in the... 

Solid crystals — If a crystal contacts a foreign substrate (the working electrode) the total free surface energy O of the system crystal-solution-foreign substrate is given by [i]... 

A water-dispersible surfactant wetting agent dissipates the free surface energy of particles by reducing the interfacial tension between the solid and the suspending vehicle. 

Table 4.4 Measured free surface energies of solids...

M is the molecular weight and p the density of the solid, d describes the particle size and a is a geometrical factor which depends on the shape of the particles. For approximately spherical particles with diameter d the geometry factor is a 6. According to Schindler [1967SCH] the mean free surface energy of the solid-liquid interface can be estimated by Eq. (VI1.44) ... 

The mechanical properties of the majority of crystalline materials are conditioned by their dislocation behavior. Consequently, the effect of the medium on the mechanical properties of solid bodies can be induced by interactions with dislocations and imperfections of the surface structure. The conditions at the solid-medium interface are dependent on the free surface energy. It is generally accepted that the strength of solid bodies is a value proportional to their surface energy. 

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