Hydrophilic headgroup engineering of oleochemical-derived branched nonionic surfactants for bio-based aircraft hard-surface cleaners

High-performance bio-based surfactants derived from renewable oleochemical feedstocks are indispensable for aircraft hard-surface cleaning. However, traditional branched surfactants exhibit inherent drawbacks such as complex synthetic routes and narrow feedstock sources. Additionally, the structure-activity relationships (SARs) of novel oleochemical-based branched nonionic surfactants and their synergistic effects with anionic surfactants remain poorly understood. To address these knowledge gaps, we systematically explored the SARs of three oleochemical-based surfactants (DMOE n , 12-HMEE n , and 9/10-HMEE n ) by correlating their molecular architectures with surface activity and application performance. The stability, synergism, and optimal formulations of mixtures prepared by mixing these nonionic surfactants with linear alkylbenzene sulfonate (LAS) and sodium dodecyl sulfate (SDS) were also evaluated, along with the performance of optimized formulations. The results revealed a clear SARs for these surfactants: Y-shaped congeners with smaller hydrophilic headgroups exhibited superior surface tension reduction capacity, whereas X-shaped surfactants with larger hydrophilic moieties possessed higher reduction efficiency owing to a lower critical micelle concentration (CMC). Moreover, symmetric hydrophobic alkyl chains and terminal ester moieties in the hydrophobic chains modulated surface activity by altering molecular aggregation and interfacial adsorption. All mixtures exhibited excellent stability, and strong synergistic effects were observed between nonionic and anionic surfactants. The optimal formulations were determined to be 6 # , 42 # , 86 # (LAS-based) and 31 # , 66 # , 112 # (SDS-based). These optimized formulations exhibit characteristic branched surfactant properties, including exceptional wettability, low foaming and rapid defoaming, and deliver excellent hard-surface cleaning efficiency that is comparable to both commercial XP 70 -based formulations and FMEE-derived bio-based reference systems. This work elucidates the SARs of oleochemical-based branched nonionic surfactants, lays a theoretical foundation for their performance optimization, and provides a potentially sustainable high-efficiency formulation for aircraft hard-surface cleaning.