Kapillärrätigheten

Kapillärrätigheten, often translated as capillary action or wicking, is the ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity. This phenomenon occurs in porous materials like soil, paper, and certain fabrics, as well as in narrow tubes called capillaries. The underlying principle is a combination of adhesive forces between the liquid and the material's surface, and cohesive forces within the liquid itself.

Adhesion is the attraction between molecules of different substances. In the case of capillary action, it's the attraction between the liquid molecules and the molecules of the surface they are in contact with. Cohesion, on the other hand, is the attraction between molecules of the same substance. This cohesion is responsible for surface tension, which allows liquids to resist external forces and maintain a relatively flat surface.

When a liquid comes into contact with a narrow tube or porous material, adhesion draws the liquid molecules up the walls. If the adhesive forces are stronger than the cohesive forces of the liquid, the liquid will "wet" the surface and climb upwards. The cohesive forces then pull the rest of the liquid along, allowing it to rise against gravity. The narrower the tube or pore, the higher the liquid will rise, as the surface area to volume ratio increases, making the adhesive forces more dominant. This process is crucial in many natural and industrial applications, from the transport of water in plants to the functioning of inkjet printers and the absorption of spills by paper towels.