Metal Ions Triggered Aggregation of Perfluorinated Surfactants

Despite the unique properties of fluorosurfactants, systematic studies on their aggregation behaviors remain limited, hindering the development and application of related systems. Here, we report two kinds of aggregations, weak gels, and particle-stabilized foams formed by perfluorocarbon fatty acids or their sodium salts with different metal ions. Specifically, perfluorooctanoic acid (PFOA) and perfluorodecanoic acid (PFDA) were observed to form weak gels under the introduction of Cu²⁺ in the presence of inorganic salts or suitable pH region. The weak gels with thermally reversible and pH-sensitive properties were primarily assembled via hydrogen bonding, metal-ligand coordination, and hydrophobic effect. Other metal ions, Pb²⁺, Ag⁺, La³⁺, and Ni²⁺, facilitated the generation of foams stabilized by particles rooted from PFOA or its salt, sodium perfluorooctanoate (SPFO) in aqueous solutions, on account of the formation of metal-ligand coordination and hydrophobic interaction.