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Do you know how much energy it takes to create a surface? Uncover the mystery of surface energy!
In materials science and surface science, surface energy plays a crucial role. This concept involves not only the structure and properties of matter, but also how matter interacts with the environment. Surface energy can be thought of as the change in energy caused by the intermolecular bonds that need to be overcome to create a surface. In order to deepen our understanding of surface energy, we need to explore its measurement methods, calculation methods and application scope.
Surface energy is the difference in energy between the surface of a substance and its interior, which can affect the dynamic behavior and reactivity of solids.
Measurement of surface energy
Contact angle method
The most common surface energy measurement method is the contact angle experiment. This method evaluates surface energy by measuring the contact angle of a liquid with a solid surface. Commonly used liquids are water and diiodomethane. From the contact angle readings, plus the known surface tension of the liquid, the researchers can calculate the surface energy.
As the surface energy increases, the contact angle decreases, indicating an increased interaction between the liquid and the surface.
Other measurement methods
In addition to the contact angle method, the surface energy of a liquid can be measured by stretching the liquid film. However, this method is not suitable for solids because stretching a solid membrane induces elastic energy internally. The surface energy of a solid is usually measured at high temperatures, so that the solid deforms while its volume remains roughly constant.
Calculation of surface energy
Surface energy of deformed solid
During the deformation of a solid, surface energy can be viewed as "the energy required to create unit surface area." In other words, it is the difference in the total energy of the system before and after deformation.
Surface formation energy of crystalline solids
In density functional theory, the surface energy of a crystalline solid can be calculated from the total energy of the two surfaces. The challenge here is to ensure that the upper and lower surfaces have the same properties.
Calculation of surface energy often requires obtaining energy measurements relative to different material interfaces under the same crystallization conditions.
Interface energy and wettability
Wetting phenomenon
Surface energy has an important influence on wetting phenomena. For example, when a droplet of liquid falls on a solid substrate, the substrate is considered wetted if the surface energy of the substrate changes.
Contact angle and wetting parameters
The size of the contact angle can directly reflect the wetting status of the liquid on the surface. The smaller the contact angle, the stronger the wettability; the larger the contact angle, the weaker the wettability.
When the contact angle is equal to 0°, the liquid completely wets the substrate; if the contact angle is equal to 90°, the wettability is considered to be extremely low.
Conclusion
Surface energy and its measurement and calculation methods occupy an important position in materials science, participating in all aspects from basic research to applied science and technology. This raises a question worth pondering: In future material design, how to make full use of the characteristics of surface energy to improve material performance and functionality?
