Inert and hydrophobic coating

Inert and hydrophobic coating

Parylene has hydrophobic and inert characteristics with a chemical barrier against organic and inorganic solutions, strong acids, gases, etc, characteristics that cannot be compared to other conventional coatings. This is one of the outstanding reasons for its excellence as a coating for medical devices and also as a coating approved by the FDA, that has awarded parylene broad approval for use in invasive and non-invasive devices.

The molecular structure of parylene C as observed with x-rays is tricyclic. However, when a longitudinal section is made of parylene, it can be seen that parylene has a lamellar structure resembling dense fish scales that effectively prevent the penetration of liquids, gases or acids.
Chemical sensors, that in the past had to be made while using more exotic and expensive materials, are currently made from simple, available materials, with a parylene coating that awards them the resistance to these materials that is so important, as well as the hydrophobic characteristic and the capability of elongation that is very helpful.

In the following table, data can be seen of the changes to the thickness of the parylene C coating after immersion in various solutions, and comparison with typical data of other coatings.

Legend: 1 = excellent inertness; 2 = good inertness; 3 = limited inertness; 4 = cannot be used as a coating.

Solution Immersion conditions Parylene C Epoxy Oritan
Hydrochloric acid 10 %
75 / 120min -0.28 1 2-3 3-4
Sulfuric acid 10 %
75 / 120min -0.28 1 1-2 3-4
Nitric acid 10 %
75 / 120min -0.28 1 4 4
Hydrofluoric acid 10 % 
50 / 120min +0.09 1 2 4
NaOH solution 10 %
75 / 120min -0.28 1 1-2 2-3
NH4OH solution 10 % 
75 / 120min -0.38 1 1 2-3
Hydrogen peroxide water (H2O2) 
50 / 120min 0.00 1 3-4 3-4
 n-Octane  75 / 120min +0.28 1 3 3
Toluene  75 / 120min +1.32 1 3 3
Monochlorobenzene  75 / 120min +1.04 1 4 4
Pyridine  75 / 120min +0.28 1 4 4
2-Propanol (IPA) 
50 / 120min 0.00 1 3 3
Acetone  50 / 120min -0.09 1 3-4 3-4