Liquids come into contact with solid surfaces in a variety of applications, including everyday situations such as painting walls or administering pharmaceuticals. In industry, wettability is important when, for example, manufacturing electronics or planning how to pump oil from a storage tank. In all of these applications, knowing the contact angle value is a good indicator of product performance or process success.
The contact angle is a measure of wettability
When a drop of water is placed on a solid, it spreads across the surface due to intermolecular interactions between the solid and the liquid. The water contact angle will immediately indicate the wettability of the solid. If the measured contact angle is greater than 90 degrees, the solid is said to have poor wettability and is called hydrophobic. If the contact angle is below 90 degrees, the term hydrophilic is used. In extreme cases, water can disperse completely or form a sphere on top of the solid, in these cases a fully wetted surface and a superhydrophobic surface are used, respectively.
The contact angle can be related to the adhesion of the coating
Paints are used for decorative and protective purposes. Whenever a paint is applied to a solid, the spread of the paint has a big impact on adhesion. Good wettability is usually associated with good adhesion. The wettability of the surface can be improved by various surface treatments such as plasma or corona treatment. Different types of adhesive layers are also often used. To determine how well the surface was prepared, contact angle measurements were used.
