The Ca²⁺-Tolerant Mechnism Of Anionic-nonionic Surfactant

Compared with non-ionic and anionic surfactant, there are many advantages of anionic-nonionic surfactants:a good resistance to salt, low Kraff point, high cloud point, and environmentally friendly. The anionic-nonionic surfactant has a high ability to resist Ca2+ions, EO group would combine Ca2+ions to form complexation, which reduces the effect of Ca2+ion on the polar groups, surfactant molecules precipitate hardly, thereby improving its ability to resist Ca2+ion. To get the interaction between EO group and Ca2+ion, EO number effects, the relationship of surfactant molecular anti-Ca2+capacity with number of EO units, and the differences of anti-Ca2+ions with different species anionic-nonionic surfactant, molecular dynamics simulation was used to study the aggregation behavior, interaction with Ca2+ion of alkyl sulfate and alkyl sulfonate with EO number of increased, With a view to the practical application of anionic-nonionic surfactant molecules and its molecular designed to provide theoretical guidance.Sodium dodecylsulfate (SDS) is a common type of anionic surfactants, widely used in various fields. In Chapter2, SDS and alkyl benzene sodium sulfate (SDBS); were compared by molecular dynamics simulations to investigate the differences of their interfacial aggregation behavior with EO group introduced. The EO group introduction will reduce the polarity of the charge, electrostatic repulsive force between them reduced, to form compact aggregates. Negative charge decreases of SO4group induce its interaction with Na+ions reduced. SDBS system reduces more than the SDS. EO groups exist to increase the hydration capacity of polar base and SDBS system increased more than SDS. These differences may be caused by steric effects of the benzene ring.Introduction of EO groups would increase the hydration capacity of SDS and SDBS, lower SO4group interactions with Na+ions. In Chapter3, the effect of EO group introduction is further explored on the anti-Ca2+capacity of SDS and SDBS. In SDS and SDBS systems, most Ca2+ions locate in the second hydration layer of surfactant molecules and SO4groups. In the SDES and SDBES system, part Ca2+ions would enter into their first hydration layer of SO4group and EO units, the interactions between Ca+ion with the surfactant enhanced, further analysis showed that the Ca2+ions only interact strongly with the O atom (SO4group connected with the EO groups), and its interaction with other three O atoms are rarely improved. The EO group would combine Ca+ions, limiting their migration, reduces effect of Ca2+ions on SO4group, thus avoiding the precipitation of surfactant, improving its anti-Ca2+capacity.Introduction of EO groups can increase the anti-Ca2+capacity of SDS, to get the effects of EO numbers on improving its anti-Ca2+capacity, in Chapter4, molecular dynamic simulations were used to compare the differences of the interfacial aggregation and their anti-Ca2+capacity of SDS, SDES, SDE2S, SDE3S and SDE4S. Increased number of EO, would lower surfactants interaction with Na+ions, and can improve the ability of its combination with Ca2+ions, especially when more than2EO units presence, there is a larger increase, while continues to increase the EO groups, its anti-Ca+capacity improvement is not evident.Alkyl sulfonate surfactants are also widely used in various fields, as compared with alkyl sulfates, in Chapter5, the interfacial aggregation behaviors and their anti-Ca2+capacity of SDSn and SDBSn were compared with EO groups increase. Introduction EO groups would enhance their hydration capacity of surfactant molecules, SO3and EO group. The interaction between SO3groups in SDSn molecules and Na+ions decreases with increasing EO. As for the SDBSn molecule, first EO group introduced will enhance the interaction between them, and as a further increase in EO group, their interaction decreases. SDSn molecule with3EO group introduced, Ca2+ion on SO3groups least affected, EO complexing capacity maximum of Ca2+ion, anti-Ca2+capacity of surfactant molecules is highest. As the SDBSn molecule with2EO groups introduced, anti-Ca2+capacity of surfactant molecules is greatly improved, continue to increase the EO groups, its anti-Ca2+capacity improvement is not evident.The mixtures of surfactant and polymer have always been a topic. While the researches on mixtures of anionic-nonionic surfactants and polymer are relatively lack. In Chapter6, the SDE3Sn and SDE3S are chosen to mix with polypropylene amide (PAM) and PPO-PEO polyether, respectively. When containing CaCl2, the interaction between the mixture system components and their ability to resist the Ca+were compared, the results found to contain SDE3Sn, Ca2+resistance of mixtue system with superior to contain SDE3S.