ATR-FTIR Kretschmann spectroscopy for interfacial studies of a hidden aluminum surface coated with a silane film and epoxy I. Characterization by IRRAS and ATR-FTIR

Interfacial analysis is essential in many areas of interest, for instance within the ongoing research on environmentally friendly pretreatments of metal surfaces. While studies of the hidden interface between a metal and polymer top-coat are of great importance, properties of a surface confined between two media are difficult to analyze in detail. Within the two parts of this study, ATR-FTIR spectroscopy in the Kretschmann geometry is employed as the main analytical tool to study the interface between a thermo-cured epoxy and aluminum pretreated with a silane film. The technique requires model systems based on thin metal films, but in contrast to most analytical techniques it permits the analysis of a hidden interface. Initial characterization of the silane film formed from a pH-regulated gamma-APS and BTSE solution was conducted by both ATR-FTIR Kretschmann and IRRAS spectroscopy. Absorption bands were obtained at 1250-900 cm(-1), assigned to Si-O functionalities, and at similar to 1570 and similar to 1410 cm(-1) assigned to acetate existing as a counter-ion to gamma-APS. After application of the epoxy film, interfacial alterations were detected upon thermal curing including the densification of the epoxy film, the dehydration of aluminum and the formation of molecular epoxy reaction products. Few alterations could be assigned to the silane film. Calculated spectra derived from optical data can verify experimental results and aid data interpretation, and effects of metal oxidation of aluminum were confirmed by introducing gold as an additional substrate. The results showed that ATR-FTIR Kretschmann spectroscopy is clearly a valuable tool for the study of hidden interfaces of stratified media. Copyright (C) 2011 John Wiley & Sons, Ltd.