The role of crosslinkers in epoxy–amine crosslinked silicon sol–gel barrier protection coatings

The search for chromate replacements in corrosion prevention materials has identified the use of hybrid sol–gel coatings as one, very promising approach. Appropriately functionalized hybrid sol–gel materials can be crosslinked to enhance their chemical durability and mechanical strength. In this work, we evaluate three crosslinkers used in a tetramethoxysilane–glycidoxypropyltrimethoxysilane binary sol–gel system in order to identify the role of the crosslinkers in corrosion protection. The crosslinkers examined were ethylenediamine, N-aminethylepiperazine, and diethylenetriamine. The sol–gel coatings were examined by contact angle, atomic force microscopy, and electrochemical impedance spectroscopy (EIS). Circuit modeling of the EIS results yielded valuable insights into the significant differences between the durabilities of the variously crosslinked coatings. Crosslinker hydrophobicity was identified as not playing a significant role whereas the number of reactive sites per crosslinker and the resulting morphology of the material may be an important parameter.