Why does low surface energy imply hydrophobicity?

In summary, low surface energy refers to the strength of intermolecular forces on the surface of a material. When a surface has low surface energy, it implies that there are weak interactions between the surface and other molecules, making it difficult for water molecules to adhere to it. This results in the material being hydrophobic, or water-repellent, as water molecules are unable to form strong bonds with the surface and instead form droplets or beads on the surface. This is why low surface energy is often associated with hydrophobicity.
  • #1
voila
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I don't understand why materials with low surface energy are hydrophobic and viceversa. All I can find are quick phenomenological explanations that don't quite deal with the physical (microscopic) process going on.

Could anyone provide a good microscopic picture of why it is that way? What's the role of the bonds in the material and how does it interact with the liquid to make it (or not) spread?
 
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  • #2
It's just that if the surface energy between a solid and air is unusually small, it's more likely that replacing the air with a liquid will make the surface energy larger.
 
  • #3
@hilbert2 Say you have a metal surface. How are the bondings between the metal and the liquid?
 
  • #4
voila said:
@hilbert2 Say you have a metal surface. How are the bondings between the metal and the liquid?

They are not described in the same way how actual chemical bonds are described. There's a quite good explanation here how the interface energy depends on short- and long-range forces: http://www-f1.ijs.si/~rudi/sola/seminar_surface_tension.pdf .
 
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1. Why is surface energy important?

Surface energy is important because it determines the interactions between a substance and its environment. It affects properties such as wetting, adhesion, and friction, which are crucial in various industrial and biological processes.

2. How does low surface energy relate to hydrophobicity?

Low surface energy means that a substance has a lower tendency to interact with water molecules. This results in a decreased ability to wet or be dissolved by water, making the substance hydrophobic.

3. What factors contribute to low surface energy?

There are several factors that can contribute to low surface energy, including the chemical composition of the substance, its molecular structure, and the presence of functional groups such as fluorine. These factors decrease the surface energy by reducing the attraction between the substance and water molecules.

4. Are all substances with low surface energy hydrophobic?

No, not all substances with low surface energy are hydrophobic. Other factors, such as surface roughness and chemical bonding, can also play a role in determining hydrophobicity. Additionally, some substances may exhibit both hydrophobic and hydrophilic properties depending on the surface conditions.

5. How can low surface energy be measured?

Low surface energy can be measured through techniques such as contact angle measurements, surface tension measurements, and surface energy calculations. These methods provide quantitative values that can be used to determine the level of hydrophobicity of a substance.

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