Atomistic Simulations of Micellization and Adsorption of Imidazoline-Based Surfactants Near Metal-Water Interfaces

Imidazoline-based surfactants are popular corrosion inhibitors in the oil and gas industry. These molecules are known to strongly adsorb onto the metal-water interfaces, as well as form micelles in the aqueous phase. High degree of corrosion inhibition is observed at concentrations close to critical micelle concentration (CMC). However, molecular underpinnings of the relationship between micellization and surface adsorption are not completely understood. By employing atomistic representation of imidazoline-based surfactants in explicit water, we have studied micellization and diffusion properties of these molecules as a function of micelle size and size of the alkyl tail. Furthermore, we have investigated the adsorption characteristics of these molecules at the metal-water interface and calculated free energy profiles of adsorption using umbrella sampling technique and weighted histogram analysis method (WHAM). We find that the micelle forming tendency and free energy of adsorption of these molecules depends strongly on the length of alkyl tail. The significance of inhibitor-inhibitor interactions on adsorption and micellization will be discussed.