This project has sought to develop ionic liquid-based fluorine-free foam (F3) formulations as an alternative to aqueous film-forming foams (AFFF) for liquid fuel firefighting in the Department of War. AFFF were used in the military, aviation, and oil industries for gasoline fire suppression. AFFF traditionally contain per- and polyfluoroalkyl substances (PFAS) that are environmentally persistent. The call for the complete elimination of PFAS chemicals triggered the development of F3 alternatives. Ionic liquids are non-toxic chemicals and are unique because of their ability to attach to a variety of functional groups.

Ionic liquids are non-toxic and unique because of their ability to attach to a variety of functional groups. Benchtop testing showed that ionic liquid surfactants, when mixed with poly(trisiloxane) surfactants, have potential as a solution to fight against pool fires. In this research project, the synergistic effect of ionic liquids (ST 26 mN/m) with lower surface tension-poly(trisiloxane) surfactants (ST 20 mN/m) and the significance of the chemical structure of ionic liquids in the fire quenching performance are studied. Increasing the foam stability of formulations were attempted using various additives. Low surface tension fluorine-free ionic liquids-based surfactants, when mixed with poly(trisiloxane) surfactants, showed firefighting performance against gasoline and heptane fuels. Ionic liquids enhanced foam spread and fire extinction properties of poly(trisiloxane) surfactants, possibly through the Marangoni effect. This research work also showed that the chemical structure of ionic liquid surfactants plays a critical role in quenching fire. Improvements in fire-suppression properties through the incorporation of proprietary additives and mixture of solvents were also explored. The firefighting foam Formulations (3% concentrates) included ionic liquid surfactants, poly(trisiloxane) surfactants, polysaccharide foam stabilizers, and a mixture of organic and water solvents. The type and ratio between ionic liquids and trisiloxane polymers were modified to evaluate the fire-quenching capacity of the resulting formulations. The foam stabilizers, hydrocarbon surfactants, and solvent mixtures were tested to improve the foam stability on top of gasoline fuel. The ionic liquid/poly(trisiloxane) formulations were tested using small bench-scale fire extinguishing tests as well as large-scale 28‑ft² pool fire tests were conducted using heptane and gasoline fuels. 

Several formulations have been tested; however, a viable formulation for MIL-SPEC fire testing has not been achieved. It is significant to note that there is no known literature on the use of ionic liquid surfactants in firefighting foams.  While the fire extinguishing properties of these surfactants were exemplary in the benchtop system (19-cm diameter pool fire), MIL-SPEC extinction tests in 28‑ft² pools did not produce similar results, and the fire extinction properties were inferior. This dramatic difference between the benchtop and MIL-SPEC firefighting performance warrants further investigations into the mechanism of fire suppression and the effect of foam quality, foam expansion, scalability, and stability under different conditions of operation.

This study helped to understand the interaction of mixed surfactants with fuels, which helped in the design of F3s that can meet the performance requirements of the MIL-PRF-32725 standard. This study explored ways to increase the foamability (expansion of foams), foam stability over hot fuel, and rate of foam spread through the addition of proprietary additives. (Project Completion - 2026)