1. Surface energy
In surface physics, the surface energy in the strict sense should refer to the internal energy of the material surface, which includes the kinetic energy of atoms, the potential energy between atoms, and the kinetic and potential energies of atomic nuclei and electrons in the original particle. Because the absolute value of surface internal energy in this sense cannot be measured, surface free energy is often used to describe the change of material surface energy. Its physical meaning refers to the isothermal reversible work consumed to produce a new surface of 1 cm². When the liquid is in equilibrium, the spherical shape is always taken, because the surface area is the smallest and the surface energy is the lowest. The outer surface of a solid is always composed of several crystal planes with different atomic arrangements, and a solid with a certain volume must form the shape with the lowest total surface free energy.
2. Surface tension
Surface tension is a physical manifestation of surface energy, which is caused by the force between atoms and the difference in the arrangement state between the surface and the interior . The surface tension γ of solid metal is usually measured by two methods: one is to obtain the specific heat capacity of the surface from the difference between the specific heat capacity of the crystal and its powder, and to calculate γ from the corresponding temperature change ; the other is to use the cleavage single crystal full It is necessary to work long to show γ, but due to the variety of surfaces on the surface, the complex microscopic morphology of the surface, and the degree of lattice defects are not the same, it is difficult to measure the accurate value.
There is a close relationship between surface tension and surface free energy. The molecules of a liquid move easily when the surface is stretched. The distance between liquid molecules does not change, but some molecules in the liquid phase migrate to the liquid surface, so the surface free energy and surface tension of the liquid are mathematically equal. But solid atoms can hardly move work, and its surface is not easy to shrink or deform like liquid, so the structure of solid surface and atoms basically depends on the manufacturing . When a solid surface is stretched or compressed, only the spacing between its surface atoms is changed. The number of surface atoms cannot be changed .
