Oberflächenspannungsprüfung

Oberflächenspannung is a physical property of liquids that describes the tendency of liquid surfaces to shrink into the minimum surface area possible. It arises from the cohesive forces between liquid molecules. Molecules within the bulk of the liquid are attracted equally in all directions by neighboring molecules. However, molecules at the surface experience a net inward force because there are no molecules above them to counterbalance the attraction. This imbalance of forces causes the surface molecules to be pulled inward and sideways, creating a tension at the surface.

This surface tension is responsible for several observable phenomena. For instance, it allows small insects like water striders to walk on water. It also causes water droplets to form a spherical shape, as a sphere has the smallest surface area for a given volume. 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 result of surface tension combined with adhesive forces between the liquid and the surface of the tube.

The strength of surface tension varies depending on the liquid. Water, for instance, has a relatively high surface tension due to strong hydrogen bonds between its molecules. Other liquids, like alcohol or oil, have lower surface tensions. Surface tension can be reduced by adding surfactants, which are substances that lower the surface tension of liquids. This is why detergents are effective at cleaning, as they reduce the surface tension of water, allowing it to spread more easily and wet surfaces better.