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)(5)(PO)(10)(EO)(5), 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. (C) 2020 Elsevier Inc. All rights reserved.

Automated summary

This study used molecular simulations to investigate the adsorption and interactions between polycyclic aromatic compounds (PACs) and non-ionic surfactants at water/oil interfaces. The findings revealed the complex interplay between PAC-surfactant interactions, PAC solubility, and the structure-dependent PAC aggregation. Different non-ionic surfactants were found to have different effects on the adsorption of PACs at the interfaces, with some inducing desorption and others enhancing adsorption. The study also identified how the roles of non-ionic surfactants can be affected by their concentration, as well as the solubility and interfacial behaviors of the PACs.