Effect of silanes on the interfacial compositions of epoxy/metal adhesive bonds: XPS and RAIR analyses

Abstract

AbstractThe effects of silanes on the interfacial compositions of adhesive bonds formed by curing silanes with the epoxy/amidoamine adhesive against clean and oiled cold‐rolled steel (CRS) and electrogalvanized steel (EGS) substrates are studied using x‐ray photoelectron spectroscopy (XPS) and reflection absorption infrared spectroscopy (RAIR). Silanes used are N‐(2‐aminoethyl)‐γ‐aminopropyltrimethoxy silane (γ‐AEAPS), γ‐glycidoxypropyltrimethoxysilane (γ‐GPS) and γ‐mercaptopropyltrimethoxysilane (γ‐MPMS). The XPS results show that the addition of silanes to the adhesive increases the number of C—O bonds and decreases the N/C ratios in the resins of the interfacial regions. The addition of silane could help the adhesive bond with the oiled substrates. The RAIR results confirm that adding various silanes to the adhesive can change the compositions in EGS/adhesive interfaces differently and affect the preferential adsorption of amino groups from the adhesive on the EGS surface. Silanes can also increase the protonation of amino groups in the adhesive on the clean and the oiled CRS surfaces. However, the absence of protonated amino groups in the adhesive/EGS interfaces indicates that the protonation is metal dependent. X‐ray photoelectron spectroscopy detects two S 2p species in the bonding interface of the specimen prepared using γ‐MPMS‐added adhesive cured against EGS substrate. The higher binding energy S 2p is attributed to the chemical reaction of mercapto groups in the γ‐MPMS with the zinc surfaces.