Understanding the Interfacial Behavior of Typical Perfluorocarboxylic Acids at Surfactant‐Coated Aqueous Interfaces

Abstract

AbstractSea surface microlayers (SMLs) play an important role in the transport and fate of surfactants from both anthropogenic and biogenic sources. The formation of sea spray aerosols (SSAs) at the SML has been recognized as a critical pathway for the entry of surfactants into the atmosphere. Perfluorocarboxylic acids (PFCAs) have become increasingly concerning as a class of emerging organic pollutants, having high enrichment in surface seawaters due to their remarkable surface activity. Using artificial seawater coated by extensively existed surfactants, including stearyl alcohol (C18OH) and stearic acid (SA) as simplified models of the SML and fresh SSAs, the interfacial behaviors of soluble and insoluble PFCAs were examined. Information about lateral packing and chain conformation of films was obtained by means of Langmuir trough and infrared reflection‐absorption spectroscopy (IRRAS). Perfluorooctanoic acid (PFOA) dissolved in aqueous subphases was found to be incorporated into lipid monolayers via alterations in surface pressure‐area (π‐A) isotherms. With negligible solubility, perfluorotetradecanoic acid (PFTA) formed condensed mixed monolayers with other lipids at the air‐water interface. The mixed monolayers of C18OH/PFTA and SA/PFTA were expanded by the addition of sea salts into the pure water subphase. Compared with the π‐A isotherms of SA/PFTA, decreased molecular areas were observed for those of C18OH/PFTA. This research suggests that PFCAs can be incorporated into air‐water interfaces by acting as film‐forming materials. The introduction of PFCAs will alter the surface properties and thus the atmospheric fate and behavior of SSAs and SMLs.