Silane-incorporated epoxy coatings on aluminum alloy (AA2024). Part 2: Mechanistic investigations

• Silane-laced epoxy coatings exhibit “self-healing” effect.
• Silane component leaches from the coating bulk to the defects during immersion.
• Different silanes have distinct protection mechanisms.
• Phase separation takes place in coatings laced with immiscible silanes.

In the second part of this series work, the protection mechanism of epoxy–silane coatings was further investigated by combined use of sum frequency generation vibrational spectroscopy, FTIR mapping, XPS and AFM, from the microscopic point of view. Results showed that silane components, no matter γ-aminopropyltrimethoxy silane or bis-1,2-[triethoxysilyl] ethane, enhance the ordering of functional groups and exhibit healing effect and thus provide improved corrosion performance of superprimers. Phase separation was detected in epoxy coatings laced with immiscible bis-silane. Such phenomenon was gradually disappearing with prolonging the immersion, as a result of phase re-organization caused by the cross-linking reaction between silanes.