POLARIZED GRAZING ANGLE FTIR STUDY OF MOLECULAR-ORIENTATION AND BONDING OF THIOGLYCOLATES AT THE METAL INTERFACE

The mercaptoesters have been recognized as an effective coupling agent for bonding metals using acrylate and epoxy adhesives with enhanced b onding strength and improved durability. Here, we report the results o f our investigation of the interaction of thioester coupling agents wi th a gold surface using a grazing angle FTIR (GA/FTIR) spectroscopic t echnique. We investigated the interaction of alkyl functional thioeste rs (octylthioglycolate, dodecylthioglycolate and stearylthioglycolate) coupling agents with the metal at the interface region. The formation of strong chemical bonding is proven to be the key feature of this ap plication rather than wetting or hydrogen bonding for conventional adh esive applications. Based on our results we have concluded that the de posited layers exist as thioester bonded to the gold surface through t he sulfur-metal bond and that the polarization results indicate that o nly those thioesters containing C-12 and C-18 hydrocarbon tail chains self-assemble readily and close pack on the surface. For dodecyl thiog lycolate, the C-12 alkyl chains are densely packed and oriented perpen dicular to the substrate surface. For the stearyl thioglycolate, the C -18 alkyl tail chains are also closely packed and oriented, but the ch ains appear to tilt from the normal surface. However, the carbonyl gro up of the C-18 thioester appears to be parallel to the surface, For sh ort-chain mercaptoesters, such as octyl thioglycolate, the alkyl chain s do not self-assemble or orient on the gold surface. The molecular or ientation of the coupling agent at the interface region has also been shown to play an important role in determining the interaction of the adhesive with the coupling agent layers, Results of the interfacial sh ear strength promotion on mild steel by the mercaptoester coupling age nts are also reported.