Effect of Heat Treatment on the Structure of Self-Assembled Undecenyl Phosphonic Acid Layers Developed on Different Stainless Steel Surfaces

Deterioration caused by corrosion is well known, which can destroy metallic and non-metallic materials alike. Dissolved inhibitors of bionic micro- and nanocoatings can decrease the degree of undesirable corrosion in various ways. In this paper, a self-assembled molecular layer formed from undecenyl phosphonic acid developed on two different steel surfaces was the subject of our experiments. The influence of the metal composition, layer-forming conditions and post-heat treatment was documented by wettability measurements as well as surface roughness parameters; the change in surface morphology caused by the formation of a layer in addition to post-heat treatment was visualized by an atomic force microscope (AFM); and infrared spectroscopy elucidated the bindings of the amphiphilic molecules involved in the self-assembled layer to the metal surface as well as to each other. Over the course of the self-assembling process, the –P(O)(OH)2 head groups can fix the amphiphilic molecule to the solid surface through the metal oxide-hydroxide layer. The hydrophobic alkenyl chains remain together as a result of special forces, namely hydrogen bonds and van der Waals forces, between them. The double bond at the end of the alkenyl chain disturbs how well the layer is ordered. To improve the homogeneity of the molecular layer and increase its level of compactness, the self-assembled molecular (SAM) layer was heat treated to achieve a more compact molecular film that can perfectly cover the metal surface.