Microscopic influence mechanisms of polysaccharide on the adsorption and corrosion inhibition performance of imidazoline on metal surface

Microbiologically influenced corrosion caused by biofilm adhesion is the most complex type of corrosion in the oil–gas pipeline. However, the mechanism of biofilm extracellular polymeric substances’ main components that influence the performance of corrosion inhibitors remains unclear. Therefore, molecular dynamics simulations were performed to gain insights into the aggregation and adsorption of alginate and imidazoline, representative compounds of extracellular polysaccharide and corrosion inhibitor, respectively, on iron surface. Results demonstrated that the corrosion inhibition of imidazoline was mainly due to the formation of a regular bilayer structure at high concentration that provided mass transport barrier and effectively expelled the corrosive Cl^- and water from metal surface. However, this capability disappeared when high concentration alginates pre-adsorbed on the metal surface. It was mainly attributed to the fact that the alginates significantly decreased the imidazoline coverage on metal surface (up to 84%), wherein the majority of imidazoline molecules suspended in the bulk water. Moreover, high concentration alginate could form porous network structure with permeable channels, which allowed Cl^- and water to pass through and approach the metal surface.