Regarding to the barrier protection, this consists in protect
the metal surface blocking the passage of oxygen and water.
Usually, the protection by barrier effect provided by a coating is
evaluated using immersion assays, in which both the volume of
water and oxygen that enters into the system and the rate of penetration
are measured [24,26]. The structure of the polymers is
essential to decide the extent of permeation through it. Indeed,
the relationship between structure of polymers and their permeability
has been successfully exploited in applications like
membranes and packaging. However, in coating applications
the presence of pigments and additives can alter the porosity
and adherence of the films modifying their protective action.
For instance, pigments reduce the porosity of the coatings; the
smaller the pigment particles, the lower the porosity [27].