Okay, we know the surface energy. Do all objects have surface energy? Of course, as long as an object has a surface, it has a surface energy. All objects must have surfaces, so they all have surface energy, solids, liquids and gases. Generally speaking, the surface energy of solids is relatively large, that of water is relatively small, and that of oil is even smaller.
So what is the relationship between surface energy and lyophilicity?
You have to know what is sparse and what is pro. Simply put, it is the contact angle, that is, whether the liquid on the solid surface spreads into a pool or remains in the state of water droplets. Extremely speaking, the contact angle of 0 degree is to spread out, and 180 degree is to completely maintain the state of water droplets. There are two lines between 0 and 180 degrees, which are 90 degrees and 150 degrees respectively. If it is less than 90 degrees, we think it is lyophilic; If it is greater than 90 degrees, it is lyophobic; If it is greater than 150 degrees, it is what we call hyperlyophilia.
In addition to hydrophobicity, there is also a parameter that affects "non-wetting", which is the rolling angle. As the name implies, the rolling angle is the angle at which the surface inclines to the point where the water drops can just roll down. It should be emphasized here that the rolling angle is not necessarily low on the surface with ultra-high contact angle. The contact angle of some surfaces can reach more than 150 degrees, but the rolling angle can also be about 90 degrees. This concept is more complicated, so I won't expand it here.
If liquid wants to spread on the solid surface, it is necessary to expand the surface area, so expanding the surface area will increase the surface energy, and energy cannot appear out of thin air, so there must be an energy provider. For the solid surface with high surface energy, the surface area of the solid is reduced by the spreading of droplets on the surface, and the surface energy is also reduced accordingly, so this part of energy can be used as the energy provider of the liquid to expand the surface area. The higher the surface energy of a solid, the higher the energy it can provide, so the liquid can be spread comfortably.
Therefore, the only way to prevent the comfortable diffusion of liquid is to make the energy provided by solids insufficient. When the reduced surface energy of solid is less than the increased surface energy of liquid, the liquid will not spread, so the preparation of liquid-repellent surface is transformed into the preparation of low surface energy solid.
Heaven has eyes. Not all solid substances have high surface energy. Many solid substances have lower surface energy than water, such as common fluoride, which is called surfactant. Therefore, if the surface energy of the solid material itself is relatively low, the hydrophobic surface can be directly prepared.