(286d) Understanding the Aqueous Solubility and Adsorption Behavior of Surfactant Molecules on Metal-Water Interfaces Using Atomistic Simulations

Adsorption of surfactant molecules on metal surfaces is useful in many applications, such as corrosion inhibition, and synthesis of anisotropic metal nanoparticles, etc. We have studied the adsorption free energy of cationic and uncharged surfactants in different aggregation states via all-atom molecular dynamics simulations. In the un-aggregated state, both types of surfactants adsorb strongly without experiencing any free energy barrier. Adsorption of micelles is, however, different for cationic and uncharged surfactants. Cationic micelles experience a long-range repulsion from the metal surface because of the presence of a corona of counterions and hydration layer around them, which gets disturbed as the micelles approach the surface. Uncharged micelles, on the other hand, undergo a barrier-less adsorption because they lack a corona of counter-ions. Upon adsorption, both types of micelles slowly disintegrate in the timescale of 200 nanoseconds to strongly adsorb on the metal surface.

Along with the direct adsorption onto the metal surface, high aqueous solubility is another desirable characteristic of the surfactants for different applications. We have performed free energy calculations at the air-water interfaces to study the hydration free energy of surfactant molecules. We propose that an addition of a polar moiety, such as a hydroxyl group, to the terminal end of the alkyl tail improves the solubility of the surfactants by three orders of magnitude.