Revealing foam stability for cationic and zwitterionic triethylsilyl-containing surfactants

A fundamental understanding of surfactant structure–property–performance relationships will inform the design next-generation alternatives to perfluoroalkyl substances (PFAS) in aqueous film-forming foams. This manuscript describes synthesis, solution properties, and foam stability novel triethylsilyl-containing surfactants, which elucidated influence hydrophilic head group on critical micelle concentration (CMC), surface tension, stability. Photocatalyzed hydrosilylation triethylsilane N,N-dimethyl allylamine yielded N,N-dimethyl-3-(triethylsilyl)propane-1-amine. Subsequent functionalization with either propane sultone or bromoethane afforded zwitterionic sulfobetaine surfactant, 3-(dimethyl(3-(triethylsilyl)propyl)ammonio)propane-1-sulfonate (TESDMAPS) cationic quaternary ammonium N-ethyl-N,N-dimethyl-3-(triethylsilyl)propane-1-ammonium bromide (TESDMABr), respectively. Dynamic light scattering cryo-transmission electron microscopy (TEM) characterized size shape solutions above CMC. Surface tensiometer analysis determined minimum TESDMAPS TESDMABr tensions 37.7 35.9 mN/m, Molecular dynamics simulations related this decrease tension a larger average interfacial area 88 Å2 per molecule compared 66 molecule. Steady-shear rheological measurements showed consistent exponential viscosity-scaling between ≤ 30 wt. %. Above concentration, displayed viscosities greater than TESDMABr, mixture surfactants provided an intermediate dependent viscosity scaling. revealed foams longer 25% drainage times TESDMAPS. The oscillatory rheology demonstrated solid-like behavior at low shear rates. Finally, polarized light-imaging highlighted formation birefringent structures under shear. For first time, work relates viscoelasticity from shear-induced assembly implications fluorine-free, next-generation, fire-fighting