A better understanding of the aggregation behavior of environmentally-friendly surfactants is required to identify, develop, and deploy functional additives to enhance the fire suppression performance of mature and emerging per- and polyfluoroalkyl substances-free fire suppressants. Aggregation behavior and differences between surfactant hydrogen-bonding networks may dictate additive compatibility in fire-fighting formulations, resulting in certain additive chemistries being beneficial to some formulations, but detrimental to others. Environmentally friendly alkylpolyglycoside surfactants (APG) have demonstrated synergism in fire suppression with siloxane surfactants; however, this synergism appears to be disrupted with additional components to the aqueous solution. The project aims to quantify differences in surfactant Hydrogen-bonding (H-bonding) networks and aggregation behavior to better understand surfactant synergism and additive compatibility for surfactants relevant to firefighting foams.

The project team hypothesizes that synergism in foam fire suppression, observed in mixtures of siloxane and APG surfactants, is related to the unique aggregation behavior of the APG surfactant. Previous research suggests APG aggregation behavior is based on inter-surfactant hydrogen bonding and this project aims to further understand the correlation between mixture aggregate behavior, inter-surfactant H-bonding, and synergism in foam fire suppression. This project is aimed at quantifying the inter-surfactant H-bonding networks of surfactant and additive mixtures, combining expertise and instrumentation at the U.S. Naval Research Laboratory (NRL) and Lawrence Berkeley National Laboratory (LBNL). NRL will identify a representative set of mixtures that did and did not show synergism in fire suppression as well as mixtures in which synergism was disrupted with additives. Solution properties such as surface tension, solution viscosity, and aggregate size will be characterized at NRL at varying temperatures and concentrations. Using a variety of spectral and imaging techniques, LBNL will quantify H-bonding within the surfactant and mixture solutions relying on collected solution property data to relate spectral information to aggregate behavior. Metrics taken from the spectral assessment of H-bonding networks will then be correlated to synergism in foam fire suppression, providing a better understanding of synergism in surfactant mixtures and a potential metric for screening surfactant synergism.

A deeper understanding of surfactant synergism aims to accelerate the development of fluorine-free firefighting foams, providing the understanding necessary to combine ineffective surfactants into mixtures and introduce additives that do not disrupt synergism. By focusing on APG, a class of inexpensive, environmentally-friendly surfactants, the project team also gains a better understanding of this surfactant and its potential to replace harmful surfactants in other commercial products. The unique properties of these surfactants must be understood further if they are to replace surfactants with different aggregation properties. This study would also benefit other industries that rely on foam stability, such as enhanced oil recovery and water-oil emulsions, as an understanding of surfactant synergism may allow these industries to utilize cheaper, more environmentally-friendly APG surfactant mixtures.