Altering aggregation behavior of surfactants and surfactant mixtures and examining the effects on foam fire extinction

Tuesday, April 30, 2024

5:00 PM – 6:00 PM EDT

Presenting Author(s)

KH

Katherine Hinnant, Dr.

Chemical Engineer
US Naval Research Laboratory
Washington, DC, United States

Co-Author(s)

SG

Spencer Giles

Former Chemist
US Naval Research Laboratory, United States
HM

Houston Miller

Professor
George Washington University, United States
RA

Ramagopal Ananth

Chemical Engineer
US Naval Research Laboratory, United States

Abstract: Surfactant mixtures demonstrate synergism in a variety of applications, including foam fire suppression. A siloxane (502W) and alkylpolyglycoside (G225) surfactant mixture can rapidly extinguish a 19cm heptane pool fire while foams containing only the individual surfactants cannot extinguish the fire. Hydrotropes sodium benzene sulfonate and sodium p-toluene sulfonate were added to individual surfactant and surfactant mixture solutions to alter micelle size. Pre-screening of the solution surface tension, viscosity, and micelle size (measured via dynamic light scattering, DLS) was conducted to define hydrotrope concentrations that altered micelle size while keeping other solution properties constant. Foam fire suppression performance was evaluated through extinction of a 19cm heptane pool fire. Without hydrotropes, DLS measured 502W micelles 15±6 nm in diameter. Their addition increased the average micelle size of the 502W solution and the error in micelle size. DLS becomes less accurate as the micelles become less spherical and transition to other shapes. G225 showed high error in micelle size without hydrotropes, indicating the non-spherical nature of alkylpolyglycoside micelles. It was difficult to quantify the effect of hydrotropes on G225 micelles due to high error with and without the additives. 502W showed improved fire extinction performance with hydrotropes, but both additives destabilized the G225 and mixture foams. Mixture fire extinction times increased. We hypothesize that hydrotropes destabilize G225 aggregation, which may be governed by inter-surfactant hydrogen bonding. 502W has a lower inter-surfactant hydrogen bonding potential and is therefore not destabilized by the hydrotropes. Probing G225 aggregation is challenging due to inaccuracies in DLS measurements for non-spherical micelles. Small angle neutron scattering (SANS) and high resolution absorption spectroscopy must be considered to better understand G225 aggregation and its role in foam fire suppression.