Cohesion is a physical phenomenon that describes the ability of molecules of a substance to stick and stay together. This phenomenon plays an important role in chemistry and physics, especially when considering liquids and solids. In liquids, cohesion is the force that causes molecules to stick together and form a cohesive mass.

These forces can vary in strength and depend on the type of liquid and molecules. For example, water has high cohesion, which means it is able to generate surface tension and form droplets.

In solids, cohesion is the force that causes the material's atoms or molecules to bond together and stabilize the material. These forces also depend on the type of material and can vary from molecule to molecule.

In adhesives, cohesion refers to the forces that hold the adhesive together. On the one hand, these cohesive forces determine the toughness (viscosity) and the dripping behavior (rheology) of the not yet solidified adhesive and thus, among other things. its processing properties.

On the other hand, together with the adhesion forces, they determine the strength of the bond against mechanical stress. The cohesive forces in an adhesive are described by parameters such as tensile strength, elastic modulus, elongation at break, or Shore hardness and should not be confused with the strength properties of a bond such as lap shear strength and shear modulus.

Overall, cohesion is an important concept in physics and chemistry that helps understand the properties of liquids and solids and explains the role of the interaction between molecules in materials and systems.