Molecular Structure of Interphases Between DGEBA/BTDA Adhesives and Silver Substrates Using Surface-Enhanced Raman Scattering

Abstract Surface-enhanced Raman scattering (SERS) was used for the non-destructive characterization of interphases between epoxy/anhydride adhesive systems and silver substrates. The normal raman spectrum of benzophenone tetracarboxylic dianhydride (BTDA) was characterized by strong bands near 1785 and 1860 cm−1 that were assigned to the anhydride groups, a strong band near 1690 cm−1 that was assigned to the benzophenone C─O stretching mode, and by a strong band near 1620 cm−1 that was attributed to vibration v(8b) of the benzene rings. The bands due to v(8b) and to the benzophenone C─O stretching mode were prominent in the SERS spectrum of BTDA but the bands related to the anhydride group were missing, indicating that the anhydride groups were hydrolyzed at the silver surface to form carboxylate groups. A band related to a CH out-of-plane bending mode which was absent from the normal Raman spectrum of BTDA was strong in the SERS spectrum, indicating that the molecules were adsorbed onto silver with a flat configuration. SERS spectra obtained from a diglycidyl ether of bisphenol-A (DGEBA) epoxy cured against a silver substrate using BTDA as the curing agent were identical to SERS spectra of BTDA and were independent of the epoxy/BTDA ratio, indicating that the spectra were characteristic of the interface rather than the bulk adhesive and that BTDA was preferentially adsorbed onto the silver substrate. SERS spectra obtained from thin films of BTDA adsorbed onto silver and then overcoated with thick films of epoxy were identical to the spectrum of BTDA and showed no evidence of bands related to DGEBA, supporting the conclusion that the SERS spectrum obtained from the DGEBA/BTDA adhesive was characteristic of the interfacial region. Key Words: Raman scatteringsurface-enhancedadhesivesepoxy/anhydridebenzophenone tetracarboxylic dianhydridediglycidyl ether of bisphenol-Ainterphasesdurability