*2.2.2 Static contact angle and dynamic contact angle*

During the measurement, the contact area between liquid and solid is not changed from outside, but the dynamic contact angle can produce during wetting (advancing angle) or de-wetting (receding angle). Besides water droplets, other organic liquids can be also used for testing the surface wettability. When oil on a solid substrate, it can be observed four fundamental states: oleophilic, oleophobic, superoleophilic, and superoleophobic.
