Physica B 385–386 (2006) 924–926 The application of neutron reflectometry and atomic force microscopy in the study of corrosion inhibitor films Douglas John a,Ã , Annabelle Blom b , Stuart Bailey a,b , Andrew Nelson a,b , Jamie Schulz a,b , Roland De Marco a,b , Brian Kinsella a,b a Western Australian Corrosion Research Group, School, Curtin University of Technology, Western Australia 6845, Australia b School of Chemistry, University of Sydney, New South Wales 2006, Australia Abstract Corrosion inhibitor molecules function by adsorbing to a steel surface and thus prevent oxidation of the metal. The interfacial structures formed by a range of corrosion inhibitor molecules have been investigated by in situ measurements based on atomic force microscopy and neutron reflectometry. Inhibitors investigated include molecules cetyl pyridinium chloride (CPC), dodecyl pyridinium chloride (DPC), 1-hydroxyethyl-2-oleic imidazoline (OHEI) and cetyl dimethyl benzyl ammonium chloride (CDMBAC). This has shown that the inhibitor molecules adsorb onto a surface in micellar structures. Corrosion measurements confirmed that maximum inhibition efficiency coincides with the solution critical micelle concentration. r 2006 Elsevier B.V. All rights reserved. PACS: 61.12.Ha; 68.08.Àp; 68.43.Hn; 68.37.Tj Keywords: Corrosion inhibition; Interfacial structure; Atomic force microscopy; Micelles; In situ neutron reflectometry 1. Introduction Organic corrosion inhibitors are frequently used throughout the oil and gas industry to mitigate carbon dioxide corrosion of carbon steel pipelines and associated equipment. The active constituents in these corrosion inhibitors are amphiphilic molecules that readily adsorb on the steel surface as a barrier to the corrosive aqueous fluids. Although it is well accepted that this adsorbed barrier is the generic origin of inhibition, little is known of the pertinent factors that distinguish superiority in the inhibitor performance. A vast majority of the current literature implies that this barrier exists as a continuous monolayer with only a minority of researchers hypothesiz- ing the possibility of bilayers [1–3]. Invariably it is found that the inhibitor perfomance exhibits a plateau at or above the critical micelle concentration (CMC), corresponding to that observed with surfactant adsorption on homoge- neously charged surfaces [4]. This correlation suggests that inhibitor compounds may also adopt adsorbed structures similar to those found for simple surfactants. It is therefore hypothesized that the adsorbed structure may have a significant influence on the performance of corrosion inhibitor compounds. In the search for new, superior and environmentally friendly corrosion inhibitor molecules, it is important to understand their mechanism of inhibition. Characterising the chemical and physical nature of the adsorbed inhibitor layer is a major part of understanding this mechanism. An accurate account of this character necessitates the use of surface analysis techniques that are capable of in situ measurements. Ex situ techniques are likely to cause changes either by oxidation of the metal and corrosion product film or rearrangement and loss of the inhibitor film during exposure to air and during the drying and analysis under vacuum. Neutron reflectometry in combination with atomic force microscopy provides the capability of in situ surface analysis of thin interfacial layers. These compli- mentary techniques make it possible to investigate the structure and orientation of molecules on a surface, which ARTICLE IN PRESS www.elsevier.com/locate/physb 0921-4526/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2006.05.213 Ã Corresponding author.