Coadsorption of Atmospheric Surface-Active Organics at the Aqueous Interface: A Molecular Dynamics Study

Organic compounds are key components of atmospheric aerosols and often act as surfactants in cloud droplets and fine particles. While the interfacial behavior of individual species in binary systems is fairly well-understood, less is known about interactions between multiple surface-active organics. We use classical molecular dynamics simulations to examine how short-chain (C₃) and long-chain (C₈) organics coadsorb at the air-water interface. Despite differences in functional groups and surface activity, all mixtures form mixed monolayers, with chain organization driven primarily by lateral van der Waals interactions. Importantly, coadsorption leads to interfacial behaviors distinct from those observed in binary systems, particularly due to the influence of weakly interacting short-chain molecules. These results suggest that simple additive models may not accurately predict the complex interplay between hydrophobic and hydrophilic forces in multicomponent surfactant mixtures. This has implications for understanding aerosol and cloud climate interactions and the role of organic surface films in atmospheric processes.