Infrared Transmission and Reflection Absorption Spectroscopy Study on Molecular Orientation of Long-Chain n -Alkane Amide and 2- n -Alkylimidazole Multilayers on Silver and KRS-5 Surfaces

Abstract

The thin films of cis-oleamide (OlA), steamide (StA), 2-undecylimidazole (UDIM), and 2-nonylbenzimidazole (NBIM) were prepared by spreading their solutions on Ag and KRS-5 substrate evaporating the solvent afterward, with the thickness in the range of 30–100 nm. The amphiphilic molecules in the multilayers were demonstrated to be highly organized by infrared reflection absorption and transmission spectroscopy. The orientation of the head group and the hydrocarbon chain of the amphiphiles in the film has been semiquantitatively evaluated. The C = O group of the amides, as well as the ring plane of imidazole and benzimidazole, has been proved to be parallel to the substrate surface. The CH stretching spectral features of the long hydrocarbon chain of the multilayers are quite different from the reported spectra of the stearate LB multilayer. The orientation of the hydrocarbon chain in the multilayers of StA and UDIM was evaluated to be inclined by about 30° from the substrate surface normal.