Surface tension

The stress working on a surface, which tends to reduce the surface area. The surface tension is a pulling force that is localised on the surface, e.g. liquid hot melt adhesive; its direction of action is parallel to the liquid surface. Accordingly, a liquid surface is always under tension.  
When other forces work on a droplet of hot melt adhesive, its shape deviates from the spherical one. An example of this are droplets of adhesive on a solid surface, where additional attracting forces act between the solid and the adhesive (adhesion). The more the shape of the droplet differs from the spherical and wets the solid surface, the higher the adhesion is between the solid body and the liquid adhesive. The greater the surface tension, the better the wettability (and hence also the bonding ability) of the surface.

Water droplets – creation of surface tension


Source: IVK, Die Kunst des Klebens, Abb. 6, S. 17