Extended surfactants: A well-designed spacer to improve interfacial performance through a gradual polarity transition

Four novel alkylaryl sulfate extended surfactants were synthesized by introducing a phenyl group, together with a polypropylene oxide (PPO) chain, as the intermediate polarity spacer in the extended surfactant molecules. Some characteristic properties of the novel extended surfactants were investigated in view of the effect of spacer structure on the performance of the surfactants. It is found that not only the PPO chain but also the phenyl group exerts a strong influence on the performance since these extended surfactants exhibit low cmc, great effectiveness and efficiency of surface tension reduction, high electrolyte resistance and ultralow interfacial tension comparing with the phenyl-free counterpart. It is notable that using a polarizable phenyl group as a junction unit in the intermediate polarity spacer may produce two potential effects: one is obviously resulting in a more gradual polarity transition intramolecularly than that of the PPO chain itself as a spacer; and the other is possibly forming a denser molecular packing and a thicker interfacial layer when the novel extended surfactants occupy at air/water (brine) surface or decane/water (brine) interface, which is attributed to a well-designed molecular structure in favor of forming a more gradual polarity transition zone in the interfacial layer.