Kapillarität

Kapillarität is the phenomenon where a liquid in a narrow tube or porous material moves upwards or downwards against gravity. This effect is due to the combined forces of adhesion and cohesion. Adhesion is the attraction between the liquid molecules and the molecules of the solid surface, while cohesion is the attraction between the liquid molecules themselves.

When a liquid is in contact with a solid surface, adhesion forces can cause the liquid to spread out or wet the surface. If the adhesive forces are stronger than the cohesive forces within the liquid, the liquid will be drawn up the sides of the narrow tube or pores. This upward movement is further supported by the surface tension of the liquid, which acts like a thin, elastic film. The surface tension tries to minimize the surface area of the liquid, and in a narrow tube, it pulls the liquid upwards to reduce the contact area with the air.

Conversely, if the cohesive forces are stronger than the adhesive forces, the liquid will not wet the surface, and capillary action might cause a depression in the liquid level within the tube. This is observed with liquids like mercury in glass. The extent of capillary rise or depression depends on the diameter of the tube, the surface tension of the liquid, and the contact angle between the liquid and the solid. Smaller diameters lead to greater capillary effects.

Kapillarität is a crucial process in many natural and technological applications. It plays a vital role in how plants absorb water from the soil through their roots and transport it to their leaves. In everyday life, it is responsible for phenomena like ink rising in a pen, water being absorbed by a paper towel, and the way wax travels up a candle wick. Understanding kapillarität is important in fields such as hydrology, soil science, and materials engineering.