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研究阴离子表面活性剂和阳离子之间的相互作用对于理解阴离子表面活性剂的沉淀和溶解现象具有十分重要的理论和实际意义,但关于两者相互作用的相关理论模型鲜有报道。本文采用密度泛函理论(DFT)方法研究了十二烷基苯磺酸根阴离子(DBS~-)与阳离子(Na~+,Mg~(2+)和Ca~(2+))在溶液内及气/液界面处的相互作用。在溶液内,在两种不同溶液环境中(水相和正十二烷)构建DBS~-/阳离子相互作用模型,并对其进行优化。结果表明,DBS~-能够与阳离子以双齿结构稳定结合。DBS~-与阳离子的结合能不仅取决于参与的无机盐离子种类,还与溶剂的性质有关。在气/液界面处,DBS~-与六个水分子相互作用形成的水合物DBS~-·6H_2O最为稳定。但是,无机盐离子的引入会严重破坏DBS~-·6H_2O水合物的水化层结构。本文定义无量纲参量def用来对水化层结构的变化程度进行评价。无机盐离子对DBS~-·6H_2O水化层结构破坏程度的顺序为:Ca~(2+)>Mg~(2+)>Na~+。电荷分析结果表明水化层在十二烷基苯磺酸钠(SDBS)头基与阳离子的相互作用中起了重要作用。
Studying the interaction between anionic surfactant and cation has very important theoretical and practical significance for understanding the phenomenon of precipitation and dissolution of anionic surfactant. However, few theoretical models about the interaction between anionic surfactant and cation have been reported. In this paper, the effects of dodecylbenzenesulfonate (DBS ~ -) and cations (Na ~ +, Mg ~ (2+) and Ca ~ (2+)) in solution on density functional theory (DFT) Interactions at the gas / liquid interface. The DBS ~ - / cation interaction model was constructed and optimized in two different solution environments (aqueous and n-dodecane) in solution. The results show that DBS ~ - can bind stably with cations. DBS ~ - with the cation binding energy not only depends on the type of inorganic salt involved, but also with the nature of the solvent. At the gas / liquid interface, DBS ~ - 6H2O, the hydrate formed by the interaction of DBS ~ - with six water molecules, is the most stable. However, the introduction of inorganic salts can seriously damage the hydration layer structure of DBS ~ - · 6H_2O hydrate. This paper defines the dimensionless variable def to evaluate the degree of change of hydration structure. The destroying degree of inorganic salt on the hydration layer of DBS ~ - · 6H_2O was Ca ~ (2 +)> Mg ~ (2 +)> Na ~ +. The results of charge analysis indicate that the hydration layer plays an important role in the interaction of SDBS head-groups with cations.