“Surfactant Transport at Fluid-Fluid Interfaces, from Bilgewater Emulsions to Firefighting Foams” by Dr. Cari Dutcher (WP19-1407) Class-B firefighting foams are aqueous foams that spread over liquid fuel and extinguish fires. Recent regulations require PFAS-free formulations for these fire suppressants. Bilgewater emulsions are oily emulsified wastewaters found in the lower chambers of ships. Prior to discharge overboard into open waters, the oil content in these chemically stabilized oil-in-water emulsions must be reduced to below 15 parts per million. To aid in meeting regulations, this SERDP effort seeks to provide a new mechanistic-level understanding of factors that govern both bilgewater emulsion and firefighting foam destabilization. For both systems, the role of soluble surfactant mixtures in stabilizing fluid-fluid interfaces is essential. In this webinar, measurements and models of surfactant transport to and along fluid-fluid interfaces will be presented. The presentation will summarize application of microscale measurement platforms and thin film models to study multiphase destabilization processes at length scales most relevant to the chemically stabilized emulsions and foams. This presentation also highlights results towards improved shipboard bilgewater treatment strategies and improved alternative firefighting foam performance.  

“Drop-in Synergistic Surfactants and Additives for Effective Pool Fire Suppression” by Dr. Katie Hinnant (WP20-1507) Fluorinated surfactants in firefighting foams are harmful to the environment and human health but produce foams with fire suppression capabilities currently unmatched by commercial fluorine-free foams for a variety of fuel fire threats. At the United States Naval Research Laboratory (NRL), research efforts are focused on mimicking the unique interactions between fluorinated surfactants and fuels, which we believe is key to firefighting success. While many individual fluorine-free surfactants have failed to produce the desired properties, mixtures of siloxane-containing surfactants and alkypolyglycoside surfactants have shown potential. Surfactant synergism can be enhanced through changes in surfactant structure and has been optimized through siloxane surfactant synthesis to produce a firefighting foam capable of extinguishing a 28-square-foot gasoline pool fire and a Jet-A pool fire in 66 and 22 seconds on average, respectively. Current military requirements for shore-based fluorine-free firefighting foams specify extinction in under 60 seconds on gasoline and under 30 seconds on Jet-A. Research efforts examining siloxane surfactant and mixture toxicology show similarly low toxicity in aquatic environments compared to commercial fluorine-free foams, but further work is needed to ensure low environmental risk. Continued optimization of the surfactant mixture for improved fire suppression requires a more fundamental understanding of surfactant synergism and the correlations between surfactant properties and foam fire suppression. This presentation will summarize ongoing research efforts at NRL to gain this understanding, include the development of next-generation synergistic siloxane mixtures with low viscosity, fuel generality, saltwater compatibility, low acute aquatic toxicity, and rapid-fire extinction capability.

Speaker Biographies

Dr. Cari Dutcher is a professor of mechanical engineering, chemical engineering, and materials science at the University of Minnesota, Twin Cities. Her research interests are in complex fluids and multiphase flows, including emulsions, suspensions, aerosols, and foams. Dr. Dutcher is principal investigator on SERDP-supported projects characterizing oily bilgewater emulsion and fluorine-free fire-fighting foam stability and destabilization, with a focus on the fundamental role of surfactant transport, rheology, and flow on these dynamic multiphase processes. Prior to her faculty position, Dr. Dutcher was a National Science Foundation Atmospheric and Geospace Sciences Postdoctoral Research Fellow in the Air Quality Research Center at the University of California, Davis. She received a bachelor’s degree in chemical engineering from the Illinois Institute of Technology and a doctoral degree in chemical engineering from the University of California, Berkeley.

Dr. Katherine Hinnant is a chemical engineer at the United States Naval Research Laboratory (NRL) in Washington, D.C., with 9 years of experience in fire suppression research. She uses laser-based experimental methods to probe fire environments during fire suppression and designs experiments to quantify fuel/foam interactions. She is the lead experimentalist on an NRL SERDP  program aimed at identifying environmentally friendly alternatives to fluorine-free firefighting foams and has contributed her expertise to numerous other SERDP and ESTCP fire suppression programs. Dr. Hinnant also conducts solution and chemical property assessments of firefighting foams for military qualification. She received a bachelor’s degree in chemical engineering from the University of Virginia, and master’s and doctoral degrees in chemistry from George Washington University.