Unit free surface energy

Free surface energy is the minimum work required to create an interface. The surface tension of a liquid is the free surface energy per unit of area in the bond between the liquid and the air. Thus, the minimum work required to create an interface is ... 

The total surface energy per unit area of liquids, U, is related to measurable surface tension or the specific free surface energy 7 by the thermodynamic equation... 

The surface tension, y, of a substance is identical to the free surface energy G per unit area and is the work required to alter the surface area by 1 cm. Therefore, y has the dimensions of energy per unit area and is usually expressed in ergs cm or dynes cm... 

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. 

One important relationship can be derived directly from Eq. (3.29). For pure liquids we choose the Gibbs dividing plane such that T = 0. Then the surface tension is equal to the free surface energy per unit area ... 

The free surface energy of a polymer solution may attract the polymer which forms an adsorbed layer at the surface. The number of monomers per unit volume is a function C (x) of the distance from the surface. Figure 3.30 illustrates this situation [142],... 

The specific free surface energy of a material is the excess energy per unit area due to the existence of the free surface it is also the thermodynamic work to be done per unit area of surface extension. In liquids the specific free surface energy is also called surface tension, since it is equivalent to a line tension acting in all directions parallel to the surface. 

Hence, the surface tension is also equal to the work spent in forming the unit surface area (m or cm ). This work increases the potential energy or free surface energy, (J/m = erg/cm ) of the system. This can be further explained by different observations we make in everyday life, where liquid drops contract to attain minimum surfaces. If a loop of silk thread is laid carefully on a soap film and the inside of the loop is pricked with a needle, the loop takes up a circular shape, which provides a minimum in the energy for the system (Figure 3.3). Indeed, the concept of surface tension was accepted as early as around the year 1800. The observations such as a floating metal... 

Surface Tension - The surface tension is the cohesive force at a liquid surface measured as a force per unit length along the surface or the work which must be done to extend the area of a surface by a unit area, e.g., by a square centimeter. Also called free surface energy. 

In a two-phase system consisting of two or more components the composition of the discontinuity surface (see Chapter I) may significantly differ from that of a bulk of both phases in contact. Primarily the components that lower the system s free surface energy are expected to accumulate within the discontinuity surface this spontaneous concentration of substances is referred to as adsorption. The quantitative measure of the adsorption of the /-th component, T was introduced by Gibbs, and is also referred to as the adsorption, or the surface excess ofthe amount of substance. This measure has a meaning of the molar excess of a particular component per unit interfacial area ... 

The total free energy of the system is composed of the energy of the bulk liquid and the surface liquid. The latter is equal to the surface free energy per unit area (Gg) multiplied by the surface area as shown in Eq. (2.2). Combining Eqs. (2.1) and (2.2) results in Eq. (2.3), which illustrates that the free surface energy of a pure substance is equal to its surface tension. 

A nonlinear dependence is for the free surface energy for SA samples (Table 2.7) since it is larger for SA3 than for SAl or SA23. However, the Ys value (per unit of surface area) is larger for pure AI2O3 having minimal surface area. 

Like free surfaces, interface surfaces at which materials are joined can also be represented macroscopically as discrete surfaces and can be characterized by an interface surface energy per unit area. The physical origin of this energy is essentially the same as that of a free surface. The energy density of an interface is presumably less than the sum of the free surface energies of the two materials joined at that interface, and greater than the energy densities within either of the materials at interior points remote from the interface. 

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