For a liquid, the surface tension (force per unit length) and the surface energy density are identical. Water, a special case, has a surface energy density of 0.08 J/m2 and a surface tension of 0.08 N/m.
Cutting a solid body into pieces disrupts its bonds, and therefore consumes energy. If the cutting is done reversibly (see reversible), then conservation of energy means that the energy consumed by the cutting process will be equal to the energy inherent in the two new surfaces created. The unit surface energy of a material would therefore be half of its energy of cohesion, all other things being equal; in practice, this is true only for a surface freshly prepared in vacuum. Surfaces often change their form away from the simple "cleaved bond" model just implied above. They are found to be highly dynamic regions, which readily rearrange or react, so that energy is often reduced by such processes as passivation or adsorption.
Surface energy is most commonly quantified using a contact angle goniometer and a number of different methods.
Thomas Young described surface energy as the interaction between the forces of cohesion and the forces of adhesion which, in turn, dictate if wetting occurs. If wetting occurs, the drop will spread out flat. In most cases, however, the drop will bead to some extent and by measuring the contact angle formed where the drop makes contact with the solid the surface energies of the system can be measured.
The Young equation assumes a perfectly flat surface, and in many cases surface roughness and impurities cause a deviation in the equilibrium contact angle from the contact angle predicted by Young's equation. Even in a perfectly smooth surface a drop will assume a wide spectrum of contact angles ranging from the so called advancing contact angle, , to the so called receding contact angle, . The equilibrium contact angle () can be calculated from and as was shown by Tadmor as,
In the case of "dry wetting", one can use the Young-Dupré equation which is expressed by the work of adhesion. This method accounts for the surface pressure of the liquid vapor which can be significant. Pierre-Gilles De Gennes, a Nobel Prize Laureate in Physics, describes wet and dry wetting and how the difference between the two relate to whether or not the vapor is saturated .
The surface energy of a solid is usually measured at high temperatures. At such temperatures the solid creeps and even though the surface area changes, the volume remains approximately constant. If is the surface energy density of a cylindrical rod of radius and length at high temperature and a constant uniaxial tension , then at equilibrium, the variation of the total Gibbs free energy vanishes and we have
A = 2pi r^2 + 2pi r l qquad implies qquad delta A = 4pi rdelta r + 2pi ldelta r + 2pi rdelta lAlso, since the volume () of the rod remains constant, the variation () of the volume is zero, i.e.,
On the surface: surface energy and surface tension are key measurements for the wet-out of adhesives, inks, and coatings.
Oct 01, 2010; [ILLUSTRATION OMITTED] Surface tension is a property of the surface of a liquid that is caused by the cohesion of molecules...
Strength, Surface Energy, and Ageing of Meltblown and Electrospun Nylon and Polyurethane (PU) Fabrics Treated by a One Atmosphere Uniform Glow Discharge Plasma (OAUGDP(TM))
Dec 01, 2005; ABSTRACT The One Atmosphere Uniform Glow Discharge Plasma (OAUGDP(TM)) generates a normal glow electrical discharge at 1...