Vådning

Vådning, or wetting, is the process by which a liquid spreads over and makes contact with a solid surface. In surface science, vådning describes how effectively a liquid can cover a surface, governed by the interfacial tensions between solid, liquid and surrounding phases. The degree of vådning is commonly expressed by the contact angle formed by a liquid drop on the surface: small angles indicate good vådning, while large angles indicate poor vådning.

Measurement and theory: The tendency of a liquid to spread is described by surface energies and interfacial tensions. Young's equation relates the solid–gas, solid–liquid and liquid–gas tensions to the contact angle. In practice, contact-angle measurements or estimates of surface energy are used to quantify vådning. Wettability is a key factor in coatings, adhesives, printing, and the formulation of suspensions and pastes.

Factors: Vådning depends on the chemical affinity between the liquid and solid, surface cleanliness, and roughness. Liquid properties such as surface tension, temperature and the presence of surfactants also matter. Surface roughness can modify apparent vådning through models like Wenzel or Cassie–Baxter, where textures amplify or reduce spreading depending on liquid behavior.

Applications: Good vådning ensures uniform coatings and films, effective spreading of inks, and better adhesion in bonding processes. In powder processing and pharmaceuticals, controlled vådning improves flow and granulation. In soils and agriculture, soil vådning affects water distribution and plant availability. In electronics and manufacturing, wettability influences soldering, bonding, and cleaning steps.

Methods: Common techniques to assess vådning include contact-angle goniometry, Wilhelmy plate measurements, capillary rise, and sessile drops. Wettability can be modified by changing surface chemistry, applying primers, or altering roughness and texture.