Kontakttvinkelen

Kontakttvinkelen, or contact angle in English, is the angle formed at the triple line where a liquid, solid surface and surrounding gas meet. It quantifies the wettability of a solid by a liquid and is defined in terms of the angle between the solid surface and the tangent to the liquid–gas interface at the contact line. A small contact angle (typically below 90°) indicates that the liquid spreads readily over the solid, signifying high wettability or hydrophilicity for water on a surface. A large contact angle (above 90°) implies poor spreading and hydrophobic behavior. In a perfectly wetted surface the contact angle approaches zero, while on a completely nonwetting surface it approaches 180°.

The measurement of the contact angle is usually carried out by the sessile drop method, wherein a droplet is placed on a flat substrate and the angle is measured from the droplet profile with a goniometer. The Young equation relates the contact angle to the interfacial tensions between the solid–liquid, solid–gas, and liquid–gas interfaces, providing a fundamental thermodynamic description.

Contact angle is a key parameter in many fields including surface science, coating technology, inkjet printing, and microfluidics. It is also used to assess surface treatments, such as plasma cleaning or self‑assembled monolayers, and to predict adhesion, capillary action and the behavior of droplets on textured or patterned surfaces. The concept extends to dynamic wetting, where advancing and receding angles describe hysteresis due to surface roughness or chemical heterogeneity.