ADHESIVES, GLUES AND SEALANTS
What are the chemical bonds?
Chemical bonds are defined as a set of interactions that take place in the electron shell of atoms, in order to join and form a molecule or a chemical stable compound.
In the study of adhesives, the role of chemical bonding is more important, because of its intermolecular forces; both are directly responsible for providing the adhesive bond strength and tha adhesion on the substrate. The chemical bonds are presented in both, the area of adhesion between the substrate and in the adhesive, as in the inner zone of the adhesive itself known as cohesion.
Chemical bonds can be divided into 3 groups:
Among the types or classes of chemical bonds mentioned above, the covalent bond is the one that takes place in the adhesive joints using organic adhesives based on polymers.
Covalent bonds are defined as the union that occurs between two atoms by the sharing of 2 or more electrons in its outer layer, to form a stable molecule.
A clear example is the molecule of chlorine, chlorine occurs in nature as a molecule composed of 2 atoms of chlorine, chlorine atoms are linked by a covalent bond produced by the sharing of 2 electrons.
During this process two atoms are join together to form one molecule, ignoring the molecular orbital theory, bonding / anti bonding and in order to explain it simply, we can say that 2 atomic orbital (Cl + Cl) combine to form a new molecular orbital (Cl2).
The orbital are defined as regions of the atoms or molecules where the electrons are localized.
In covalent bonds we find 2 types of covalent bonds that can arise:
polar covalent bond
non polar covalent bond
Polar covalent bond
Polar covalent bond - is caused when one atom has stronger attraction of electrons to the nucleus, as a result it produces a molecule with the negative and positive area (dipole).
The polar covalent bonds always occur during when the bond is between two different atoms.
The degree of polarity of the molecule resulting from the covalent bond depends on the strength or attraction that attracts electrons to an atom, this concept is defined by the electronegativity.
Examples of polar covalent bonds can include water, isopropyl alcohol ...
Non polar covalent bond
Non polar covalent bond - occurs when two atoms have the same force of attraction of electrons to his nucleus.
Polar covalent bond always occur when the bond is between 2 atoms equal or with the same degree of electronegativity.
The concept of a polar material is very important for the study of adhesives, usually surfaces that have molecules with polar materials will be good to apply to an adhesive.
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