Study Cards on permeable, coating, coatings

What does the bi-layer system consist of, when applying a combination of a low and high permeable film to avoid defects in coatings?
  1. Material that has a very low permeability to the undesired permeant (e.g. Water) --> lipid based film, featuring very low permeabilities, but also a low mechanical strength (brittle) --> probably will show defects
  2. Permeable material, but having optimal mechanical properties, such as high elasticity and high tensile strength. Protein-based coating. The thickness of this film may be low, it is essential that the coating material wets the previous layer. The second layer will penetrate the defects through capillary action, and fill it with second coating material.
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What are disadvantages of applying a combination of a low and high permeable film to avoid defects in coatings?
  • The primary layer should still be applied with reasonable effectiveness (the porosity should not be too high)
  • The second layer should have excellent binding properties to the material of the primary layer. The wetting behaviour therefore becomes crucial.
  • Two coating procedures is expensive.
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It is not necessary that the secondary coating has very good barrier properties. T/F
True, a lower permeability leads to a small reduction of the overall permeability of the barrier.
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