十二烷基苯磺酸钠和无机阳离子之间相互作用的密度泛函理论研究

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⁺, Mg²⁺和Ca²⁺)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^-·6H₂O最为稳定。但是,无机盐离子的引入会严重破坏DBS^-·6H₂O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^-·6H₂O水化层结构破坏程度的顺序为:Ca²⁺ > Mg²⁺ >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。

Density Functional Theory Study of the Interaction between Sodium Dodecylbenzenesulfonate and Mineral Cations

Investigating the interactions between anionic surfactants and cations is of great theoretical and practical significance to understanding the precipitation and solubility of anionic surfactant products but relevant theoretical interaction models are seldom reported. In this paper, the density functional theory (DFT) method was used to investigate the interactions of the dodecylbenzenesulfonate anion (DBS^-) with Na⁺, Mg²⁺, and Ca²⁺ both in the solution and at the air/water interface. In the solution, DBS^-/cation interaction models were built and optimized with consideration of two different solutions (i.e. water and n-dodecane). The results indicate that DBScan bind stably with the cations in a bidentate form. The binding energy of the DBS^-/cation depends on the properties of both the participating cation and the solvent. At the air/water interface, DBS^- formed a stable hydrated complex with six water molecules (i.e. DBS^-·6H₂O). However, the structure of DBS^-·6H₂O was greatly disturbed by the introduction of the cation. A dimensionless parameter, def, was proposed to evaluate the deformation extent of the hydration shell. The degree of disturbance by the cations follows the order: Ca²⁺ >Mg²⁺ > Na⁺. A charge analysis reveals that the hydration shell plays an important role in the interactions between the sodium dodecyl benzene sulfonate (SDBS) headgroup and the cation.