How Does Adhesive Bond Chemically?

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Syed Asim answered
For adhesion of smooth surfaces, the adhesive and the adherend must strongly attract each other at the interface. This is called bond. Bonding mechanisms include chemical bond, hydrogen bond, Van der Waals forces. Chemical bonds include covalent bond, semi polar bond, ionic bonds and metallic bond. However, adhesion bond is attributed to hydrogen and Van der Waals force.

The hydrogen bond is between hydrogen atoms in two molecules. The hydrogen atom in the hydroxyl group is attracted by a nearby oxygen atom and forms a hydrogen bond. For this bond, the molecules of adhesive or the adhered must contain hydroxyl, isocyanine, and carboxylic groups or another group that has polarity. In these groups the hydrogen bond is established and adhesion occurs.

The Van der Waals force is a measure of the affinity between the adhesive and adhered. In other words, adhesion occurs because of the attractive force between molecules. The Van der Waals force is attributed to the three intermolecular interactions; the orientation, induction and dispersion interactions.

Some molecules are formed with plus and minus poles having equal dielectric charge. This is called an electric dipole or a permanent dipole molecule. In contrast, molecules which do not have an electric dipole are called non-polar molecules.

When permanent dipole molecules are in contact, they arrange themselves such that the plus and minus charges attract each other. This is called orientation effect and the force is called orientation force. This force is due to polarity (dipole) of each molecule of the adhesive and adhered. When a permanent dipole molecule (polarized molecule) is close to non polarized molecules, an electric dipole is induced in the non polarized molecule. This is called induction effect and the mutually attractive force is called induction force.

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