kapillaariilmiöön

Kapillaariilmiö, often translated as capillary action, 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 is driven by a combination of intermolecular forces: adhesion, the attraction between the liquid molecules and the molecules of the surrounding solid surface, and cohesion, the attraction between the liquid molecules themselves.

When a liquid like water is in contact with a surface that it wets, such as glass, the adhesive forces between the water molecules and the glass are stronger than the cohesive forces between the water molecules. This causes the liquid to creep up the sides of the narrow tube or space, forming a meniscus. The liquid surface will then rise until the upward pull of adhesion is balanced by the downward force of gravity acting on the raised liquid column.

Conversely, if the liquid does not wet the surface, meaning the cohesive forces within the liquid are stronger than the adhesive forces to the surface, the liquid level in the narrow space will be lower than in the surrounding bulk liquid. This is observed with liquids like mercury in glass.

Capillary action plays a crucial role in many natural processes. For instance, it is responsible for how water is drawn up from the roots of plants to their leaves through xylem tissues. It also influences the movement of groundwater in soil and the wicking action of liquids in porous materials. In everyday life, it can be seen in how a paper towel absorbs spills or how a candle wick draws wax upwards. The narrower the space, the more pronounced the capillary effect.