Tuning rheology and fire-fighting performance of protein-stabilized foam by actively switching the interfacial state of the liquid film.

• Metal-ion-mediated interfacial crosslinking allow to make gel protein foam from low-viscosity solution. • Active switching between rigid and mobile states of the interfacial film was achieved. • Enhanced rheology of foam with rigid films establish robust barrier to suppress oil combustion. • A new correlation between interfacial state and the fire-fighting performance was proposed. Biomolecular self-assembly has lately emerged as an intriguing method for creating stable gas-liquid dispersions with unique functional characteristics. In this work, protein-metal coordination complexes were designed as the stabilizer for generating ultrastable fire-fighting foam and creating interfacial architectures that were actively switched between "rigid" and "mobile" interfacial states of liquid films in response to changes in pH and bulk solution compositions (metal ions or alkyl polyglycosides). The reflected light interferometric technique was used to check interfacial states, and the foaming kinetics and rheological response of aqueous solution and liquid foam were investigated by dynamic surface tension tests and oscillatory rheology analysis. The results showed that liquid foams with mobile films with lower yield limits had a faster spreading rate to cover the burning oil, liquid foams with semi-rigid films cannot extinguish fires due to interfacial instability, and the enhanced rheology of the foam with rigid films established a robust and impenetrable barrier to effectively suppress fuel evaporation and combustion. A new correlation between interfacial properties and the fire-fighting performance of foam was proposed, which showed that the fire-extinguishing time of foam could be well correlated by the interfacial states or film lifetime rather than classical thermodynamics entry, spreading, and bridging coefficients (ESB coefficients). [Display omitted] [ABSTRACT FROM AUTHOR]