Synchrotron infrared microspectroscopy study of the orientation of an organic surfactant on a microscopically rough steel surface

Abstract

The performance of organic surfactants as corrosion inhibitors is influenced by the mechanism of adsorption and the resulting molecular orientation on the substrate. The molecular orientation of 1-dodecylpyridinium chloride (DPC) deposited on non-corroded 1030 mild steel and after corrosion in a carbon dioxide environment has been investigated using synchrotron infrared microspectroscopy. DPC mitigates the corrosion process by adsorbing at the steel surface and forming a protective layer. Infrared spectra analogous to polarized grazing angle spectra were obtained from a microscopically rough surface using a synchrotron source. The appearance of negative and positive absorption bands in the spectra, when using synchrotron radiation, is discussed in terms of the optical system used. The presence of the DPC surfactant at the steel surface is shown by the CH 2 and CH 3 infrared absorption bands of the aliphatic chain of the DPC molecule. The infrared spectra provide direct evidence on the orientation of DPC at the steel substrate. The aliphatic chain of the surfactant is tilted orthogonally, but not perpendicular to the substrate plane. The absence of significant absorption bands characteristic of the pyridinium ring of DPC indicates its orientation parallel to the substrate plane, and an adsorption mechanism involving πbonding with the steel. This study demonstrates the applicability of synchrotron infrared microspectroscopy to the investigations of thin organic films on microscopically rough steel surfaces, and can facilitate further investigations of thin films on metallic surfaces and monolayer studies in general.

Carbon steel corrosion: a review of key surface properties and characterization methods

“…Synchrotron-sourced FTIR provides a better signal to noise ratio compared to conventional FTIR instruments. Lepkova et al 145 studied an organic surfactant, namely 1-dodecylpyridinium chloride (DPC), on carbon steel in CO 2 -saturated brine. Using the synchrotron-sourced FTIR, the authors detected the adsorbed inhibitor lm on the carbon steel, which was not possible with conventional FTIR.…”

Advanced Vibrational Microspectroscopic Study of Conformational Changes within a Craze in Poly(ethylene terephthalate)

“…In the case of IR synchrotron radiation, the so-called bending magnet radiation (BMR), produced by curving the trajectory of relativistic charged particles in a constant magnetic field, presents quasi-linear polarization properties that can be exploited to perform orientation analysis without the use of any further optical elements, thus taking advantage of the full source intensity, crucial when employing small apertures. − …”

Emerging surface characterization techniques for carbon steel corrosion: a critical brief review

“…A similar approach can be adopted for studying adsorption of corrosion-inhibitor molecules on carbon steel. For example, the type of π-bonding of a corrosion inhibitor molecule, namely 1-dodecylpyridinium chloride, with carbon steel has been suggested from Fourier transform infrared spectroscopy study [63]. The application of NEXAFS can further help in this type of study and provide supplementary information about bonding of inhibitor molecules with a substrate.…”