Development of a silica aerogel-based fluorine-free foam with ReaxFF molecular dynamics insights on thermal degradation and fire extinguishing mechanisms

Abstract

This study investigates the hydrophobic modification of silica aerogels using trimethylchlorosilane (TMCS) and characterises their morphology, wettability, and surface properties through SEM, FTIR, and contact angle measurements. Additionally, the foam stability, fire-extinguishing efficacy, and burn-back resistance of three foam formulations were analysed to investigate the impact of silica aerogel particles on the performance of fluorine-free firefighting foams. The results demonstrated that TMCS effectively modified the surface of the aerogel particles, imparting hydrophobicity. SEM analysis revealed the irregular polyhedral structure of the hydrophobic aerogel. FTIR analysis confirmed an enhanced C-H vibration peak in the hydrophobic aerogels and a higher hydroxyl content in the hydrophilic ones. Fluorine-free foams with added aerogel particles exhibited improved drainage times and outstanding fire-extinguishing performance. The hydrophobic particles increased the drainage time by 55 s and achieved a cooling rate of 35.27 °C/s, with a burn-back resistance time extended to 1123 s, 1.64 times that of the control. Similarly, the addition of hydrophilic aerogels increased the burn-back resistance time by 41 %. Furthermore, to deliver an in-depth atomistic description of the interactions between aerogel particles and foam components, molecular dynamics (MD) simulations using the ReaxFF force field were conducted. ReaxFF-MD revealed the key molecular-level interactions that influence foam stability and fire extinguishing, offering insights into the synergistic effects between aerogel particles and the foam matrix under high-temperature conditions.