What is contact angle? What is hydrophilic, super hydrophilic? What is hydrophobic or superhydrophobic?

A. In the following figure θ C is called contact angle, which is a measure of the degree of wetting.

Definition: Contact angle refers to the angle between the tangent line of the gas-liquid interface at the intersection of gas, liquid, and solid, passing through the boundary between the liquid and the solid-liquid interface θ C.

1) When θ C < 5 °~10 °, basic wetting, super hydrophilic;

2) When θ C<90 °, partially wet or wet, and the smaller the value, the better the wettability, indicating hydrophilicity;

3) When θ C=90 °, which is the boundary between wetting and non wetting;

4) When θ C > 90 °, non wetting, liquid surface shrinks into a hemispherical shape, indicating hydrophobicity.

5) When θ C > 150 °, completely non wetting, the liquid surface shrinks into a spherical shape, which is superhydrophobic.

B. The state in the figure below is called hydrophilic.

Zixi Lai is super hydrophilic and has a contact angle θ C approaches 5 °

C. The state in the figure below is called Hydrophobic.

Zixilai WNS superhydrophobic coating, contact angle θ C>150 ° is called superhydrophobicity.

In order to have a more direct impression, here are some examples of contact angles:

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