ABSTRACT
Matter exists as gas, liquid, and solid phases, as has been recognized by classical science. The molecules that are situated at the interfaces (e.g., between gas-liquid, gas-solid, liquid-solid, liquid1-liquid2, solid1-solid2) are known to behave differently from those in the bulk phase [1-17]. It is also well-known that the molecules situated near or at the interface (i.e., liquid-gas) are situated differently with respect to each other than the molecules in the bulk phase. Especially, in the case of complex molecules, the orientation in the surface layer will be the major determining factor as regards the surface reactions. The intramolecular forces acting would thus be different in these two cases. Furthermore, it has been pointed out that, for a dense fluid, the repulsive forces dominate the fluid structure and are of primary importance. The main effect of the repulsive forces is to provide a uniform background potential in which the molecules move as hard spheres. The attractive forces acting on each molecule in the bulk phase are isotropic when considering over an average time length. This means that the resultant net force in any direction is absent. The molecules at the interface would be under an asymmetrical force field, which gives rise to the so-called surface tension (ST) or interfacial tension (IFT) (liquid-liquid; liquid-solid; solid-solid) (Figure 1.1) [16a-c].
