Tuning sodium lauroyl surfactant foam performance via headgroup methylene modulation: synergistic mechanisms and sebum resistance

Abstract Foam dynamics of SLAt and SLGt (differing by one methylene group) were studied via dynamic foam analysis, rheology, and MD simulations. SLAt achieves optimal performance at pH 7.0: lowest surface tension (28.096 mN/m), rapid foaming, moderate foam volume (96.8 mL), large initial bubbles (4,444 µm2), and high stability. SLGt peaks under weak alkalinity with greater volume (106.2 mL) and stability (tFLS 50 % = 503.1 s), but slower foaming, smaller bubbles, and coarsening susceptibility. Synergy with co-surfactants reveals: CAB boosts foam volume (115–117 mL), SMCT enhances lipid removal in sebum systems.MD simulations show SLGt adopts extended conformations with higher hydrophilicity, improving surface tension reduction. SMCT exhibits stronger hydrophobic interactions for lipid sequestration. Hydrogen bonds between primary/co-surfactants govern foaming kinetics and volume – their quantity and spatial positions critically modulate performance. The single-methylene difference dictates pH-dependent foam behavior and lipid tolerance, enabling targeted design of mild cleansers.