Impact of Bulk Acidity and Water‐Soluble Organic Compounds on Surfactant‐Driven Particle Morphological Evolution After Liquid‐Liquid Phase Separation

Abstract

Surfactant‐containing organic‐inorganic mixed aerosols can exhibit diverse mixing states following liquid‐liquid phase separation (LLPS), ranging from core‐shell to partial engulfing and inverse core‐shell structures, thereby altering their chemical, physical, and optical properties, as well as associated geochemical processes. Despite the recognized importance of bulk acidity and water‐soluble organic compounds (WSOCs) in aerosol phase transitions, their roles in modulating surfactant‐driven LLPS morphological evolution remain poorly understood. In this study, we investigated the phase transition behavior of acidified aerosols composed of 1, 2, 6‐hexanetriol, ammonium sulfate, and sodium dodecyl sulfate (SDS), and compared the LLPS morphologies of acidified and non‐acidified SDS‐containing particles. The results show that acidification, together with the conversion of sulfate to bisulfate with a weaker salting‐out effect, significantly promotes LLPS morphological evolution. Notably, partial engulfing and inverse core‐shell structures emerge at relatively lower SDS fractions, with SDS concentration thresholds 1–2 orders of magnitude lower than those for non‐acidified particles. This situation suggests that these unexpected morphologies may be more prevalent in the atmosphere than previously recognized. Furthermore, the presence of WSOCs, such as sucrose and glycerol, in non‐acidified SDS‐containing particles can also perturb LLPS morphological evolution. These findings highlight the need to jointly consider surfactant fraction, bulk acidity, and WSOC coexistence when assessing the morphology of multicomponent aerosols, which is critical for improving high‐resolution representations of aerosol morphology in atmospheric and climate models and for advancing our understanding of aerosol‐chemistry‐climate interactions.