Grenzflächenspannungsprüfung

Grenzflächenspannung, also known as surface tension, is a property of liquids that causes the free surface of a liquid to behave like a stretched elastic membrane. This phenomenon arises from the cohesive forces between liquid molecules. Within the bulk of the liquid, each molecule is attracted equally in all directions by neighboring molecules. However, at the surface, molecules are attracted more strongly by the molecules below and beside them than by the molecules in the air or gas above. This imbalance of forces pulls the surface molecules inward and sideways, creating a net inward pull that minimizes the surface area.

The effect of surface tension is observable in various everyday phenomena. For instance, it allows small insects to walk on water, as their weight is not enough to overcome the surface tension. Water droplets form spherical shapes because a sphere has the smallest surface area for a given volume, minimizing the surface energy. Capillary action, the ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity, is also a direct consequence of surface tension and adhesive forces between the liquid and the surface of the tube.

Surface tension is measured in units of force per unit length (e.g., Newtons per meter) or energy per unit area (e.g., Joules per square meter). Different liquids have different surface tensions, influenced by factors such as temperature and the presence of dissolved substances. For example, adding soap or detergent to water significantly reduces its surface tension, which is why soap is effective at cleaning by allowing water to spread more easily and penetrate fabrics.