Particle-stabilized foams with fatty acid salts as stabilizers triggered by transition metal ions

Particle-stabilized foams have been becoming the focus on foaming field because of their excellent stability due to the high stiffness of interface membrane. However, the modification of particle surfaces to reach an appropriate wettability needs complicated process, resulting in accompanied inconvenient foaming-defoaming regulation. In this work, we reported a series of foams stabilized by insoluble particles generated from fatty acid anions with metal ions. Different hydrocarbon chains endowed the formed particles diverse wettability and different aggregation behaviors at the gas–liquid interface, e.g., different foamability and the formation of the “dry water”. The foams exhibited ultra-stable properties and were responsive to environmental acidity, thus possessing a smart foaming-defoaming transition tuned by pH. The combination ability of fatty acid anions with metal ions changed with the chain-length and the nature of metal ions, leading to a choice for the extraction or separation of some metal ions in a fast and simple way. This new aggregation behavior of fatty acid salts can be explored to expand the practical applications.