Infrared reflectance as a tool to reveal preferential molecular orientation of polymers adsorbed onto flat substrates

FTIR-Reflectance experiments have been made on thin ethylene-vinyl acetate (EVA) copolymer layers deposited on aluminum mirrors in order to determine orientation of polymer functional groups at the interface. This was accompl ished by using various reflection angles under p polarization state of the incident IR beam. Film thicknesses were estimated by ellipsometric experime nts. Kramers-Kronig analysis is first applied to the external infrared refl ection spectrum from a single copolymer surface measured near the normal in cidence angle. Absorption spectra, k(v), are then deduced and used to calcu late specular reflectance intensities of the functional groups of interest as a function of incidence angle, polarization state and film thickness. Th e calculated values are compared to those observed. A layer model is develo ped, which allows the molecular orientation of both EVA carbonyl groups and the main chain axis at the interface to be determined. Only carbonyl group s involved in specific electron donor-electron acceptor interactions at the interface appear to be subject to specific orientation. A persistence thic kness of the preferential orientation in the film is determined, also from which it is concluded that even in nanofilms, preferential molecular orient ation induced by an hydroxylated substrate does not persist throughout the film thickness. It is localized at a near interfacial region, the thickness of which depends on the ability of the comonomer to undergo conformational changes.