Interfacial energy definition

The van der Waals and other non-covalent interactions are universally present in any adhesive bond, and the contribution of these forces is quantified in terms of two material properties, namely, the surface and interfacial energies. The surface and interfacial energies are macroscopic intrinsic material properties. The surface energy of a material, y, is the energy required to create a unit area of the surface of a material in a thermodynamically reversible manner. As per the definition of Dupre [14], the surface and interfacial properties determine the intrinsic or thermodynamic work of adhesion, W, of an interface. For two identical surfaces in contact ... 

If, when a liquid drop is placed on a smooth surface, the forces of adhesion between the solid and the liquid are greater than the forces of cohesion of the liquid, then the liquid will spread and will perfectly wet the surface spontaneously. If the forces reach an intermediate balance determined by the interfacial energies ylv, ysj and ysv, then the liquid drop will form a definite contact angle (0) with the solid surface (Figure 4.12). 

However, in this formulation, G /8 is simply a fitted parameter, since there is no rigorous molecular definition for this form of the interfacial energy. In addition, this model suffers the same problem as do other continuum models, in that it contains parameters that must be determined from experimental data and that cannot be estimated a priori from molecular techniques. 

There exists as we have noted a separate phase at the interface between a liquid and a gas. The magnitude of the vapour-liquid interfacial energy is markedly dependent on the composition of the liquid and although experimental data are somewhat scanty, the surface energy is also affected by the nature of the gas in contact with it. It is to be anticipated that at the interface between two immiscible liquids a similar new interfacial phase will come into existence possessing a definite surface energy dependent on the composition of the two homogeneous liquid phases. 

The solubility product is defined for a semi-infinite plane surface where the interfacial energy between the crystal and the solution makes a negligible contribution to the free-energy of formation of the particle. The definition also necessitates that the solid phase is homogeneous in structure and that a chemical potential may be assigned to the components irrespective of their position within the solid. When the crystals are small this may not be true because the imbalance of interionic forces at the surface produce... 

The definitions in terms of an interfacial layer are useful only when K can be assessed unequivocally on the basis of a physical model of the interfacial layer or when it can be taken as negligibly small. For this model the interfacial energy is defined as before but including a contribution to the total volume from the adsorbate ... 

Using the Gibbs model, it is possible to obtain a definition of the surface or interfacial tension y. The surface free energy dG comprises three components (i) an entropy term S dT (ii) an interfacial energy term Ady, and (iii) a composition term S d/t (where W is the number of moles of component i with chemical potential nf. The Gibbs-Duhem equation is,... 

Definition of contact angle at the solid-liquid interface. 7ig denotes the liquid-the solid-liquid interfacial energy, and 7., denotes the... 

In most cases of interest, the surface excess mass E is small, so that the acceleration and body force terms may be neglected. Then Equation 1.40 simplifies to two conditions. One of them, V y = 0, requires that interfacial tension be uniform. The other is the Young-Laplace equation (Equation 1.22), which was obtained previously from thermodynamics for situations where body force and acceleration terms were unimportant. That the same equation (Equation 1.22) results from independent thermodynamic and mechanical derivations implies that interfacial tension must have the same value whether it is defined as in Equation 1.9 from energy considerations or as in Equation 1.39 from force considraations. Simply put, the force and energy definitions of interfacial tension are eqnivalrait, a conclusion emphasized in the work of Buff (1956). 

This classical definition is for any interface. The interfacial energy is a consequence of the interaction between molecules and contains contributions from mutually attractive intermolecular forces due to combined effects of dispersions, dipole, induced dipole and hydrogen bonding interactions. At short distances molecular species are repulsive whereas at longer distances the molecules become attractive. A variety of different interaction potentials can be used however, the simplest is an inverse square law, in which case the interaction energy has the form... 

Remark.- The definition of interfacial energy does not prejndge anything of its sign we further observe, in microscopic interpretation (section 8.3.2), that it is always positive in the case of the formation of a solid. 

Interfacial energy was initially introduced into the deformable systems, for example, an oil-water interface. In this case, an experimental definition is possible interfacial energy under given conditions is then the ratio of the additional energy that is necessary to be provided to the system to obtain increment of interfacial area, other sizes being maintained constant. 

In its thermodynamic definition, the interfacial energy of a solid in the presence of a fluid or another sohd is of unspecified sign. We noted in the microscopic interpretation that its value is always positive with the consequence that the formation of an interface is always imfavorable. 

Roll-up. The principal means by which oily soil is removed is probably roU-up. The appHcable theory is simply the theory of wetting. In briefest outline, a droplet of oily soil attached to the substrate forms at equiUbrium a definite contact angle at the oil-sohd-air boundary line. This contact angle (Fig. 4) is the result of the interaction of interfacial forces in the three phase boundaries of the system. These interfacial forces, expressed in mN/m(= dyn/cm), or interfacial free energy values expressed in mj/m (erg/cm s) are conveniently designated 1SA iSlj subscripts relate to the Hquid-air,... 

Components of interfacial tension (energy) for the equilibrium of a liquid drop on a smooth surface in contact with air (or the vapor) phase. The liquid (in most instances) will not wet the surface but remains as a drop having a definite angle of contact between the liquid and solid phase. 

Equation D3.5.13 illustrated that the free energy of an interfacial system can be expressed in terms of the interfacial tension and chemical potential of the overall system. A simple differentiation or alternatively the reutilization of the definition of the interfacial tension used in Equation D3.5.7 at constant pressure and temperature yields ... 

There are two common and widely used definitions of the interfacial excess enthalpy. We can argue that enthalpy is equal to the internal energy minus the total mechanical work 7A-PVa. Since in the Gibbs convention PVa = 0 we define... 

---