Perfluoroalkyl Substances Reshape Phase-Separated Morphologies of Atmospheric Organic–Inorganic Aerosols: Dependence on Perfluorocarbon Chain Length and Functional Group

Abstract

Perfluoroalkyl substances (PFAS) are ubiquitous in environmental matrices. Owing to their persistence and biotoxicity, research attention and regulatory efforts have primarily focused on their atmospheric fate and associated human health risks. However, significant knowledge gaps remain regarding their influence on aerosol physicochemical properties and related geochemical processes, particularly phase transitions and particle morphology. In this study, we investigated the phase transition behavior and liquid–liquid phase separation (LLPS) morphology of ternary mixed particles consisting of 1,2,6-hexanetriol, ammonium sulfate, and PFAS. Ultrashort-chain PFAS such as trifluoroacetic acid (TFA, nC = 2) maintained a core–shell LLPS morphology due to relatively weak surface activity. The addition of perfluorobutanoic acid (PFBA, nC = 4) shifted the morphology from core–shell to partial engulfing, whereas systems containing perfluorobutanesulfonate (PFBS, nC = 4) further evolved to inverse core–shell structures at high PFBS fractions. Long-chain PFAS, i.e., perfluorooctanoic acid (PFOA, nC = 8) and perfluorooctanesulfonate (PFOS, nC = 8), induced partial engulfing structures at relatively low fractions, while higher fractions did not result in inverse core–shell morphology. Surface tension measurements indicate that the observed LLPS morphological evolution is consistent with the surface activity of PFAS in the phase-separated organic and inorganic phases, which depends on perfluorocarbon chain length and functional group. These findings provide new insights into the regulatory effects of PFAS on the LLPS morphology of atmospheric organic–inorganic biphasic systems. The results also help clarify the associated aerosol physicochemical properties and aerosol-chemistry-climate interactions.