Effect of non-ionic surfactants on the adsorption of polycyclic aromatic compounds at water/oil interface: A molecular simulation study.

HYPOTHESIS

Molecular simulations can provide unique insights into the adsorption and intermolecular interactions of polycyclic aromatic compounds (PACs) and non-ionic surfactants at water/oil interface.

METHODS

Molecular dynamic simulations were performed to study the adsorption of PACs at water/oil interface, and the effect of adding non-ionic surfactants. PAC architecture, solvent type, structure and concentration of non-ionic surfactants were varied to address the complex interplay between PAC-surfactant interaction, PAC solubility, and structure-dependent PAC aggregation.

FINDINGS

PACs with multiple cores (PacM) partially adsorbed on the interface, in the form of small and loosely structured aggregates. Adding non-ionic surfactant Brij-93 induced desorption of PacM at both water/toluene and water/heptane interfaces. Another non-ionic surfactant, (EO)(PO)(EO), also reduced the adsorption of PacM at water/toluene interface but enhanced their adsorption at water/heptane interface. PACs with a single large core strongly adsorbed on both interfaces, forming compact aggregated structures. Adding the two types of non-ionic surfactants did not induce desorption. This work identified two opposite roles of non-ionic surfactants in the adsorption of PACs, namely competition and co-adsorption, and provided useful insights into how the roles of non-ionic surfactants might be affected by their concentration, as well as the solubility and interfacial behaviors of the PACs.