十二烷基苯磺酸钠在SiO_2表面聚集的分子动力学模拟

Molecular Dynamics Simulation of Sodium Dodecyl Benzene Sulfonate Aggregation on Silica Surface

采用分子动力学方法研究了阴离子表面活性剂十二烷基苯磺酸钠(SDBS)在无定形SiO2固体表面的吸附.设置不同的水层厚度,观察固液界面和气液界面吸附的差异.模拟发现表面活性剂分子能够在短时间内吸附到SiO2表面,受碳链和固体表面之间相互作用的影响形成表面活性剂分子层,并依据吸附量的大小形成不同的聚集结构;在水层足够厚的情况下,由于有较多的表面活性剂分子吸附在固体表面,从而形成带有疏水核心的半胶束结构;计算得到的成对势表明极性头与钠离子或水分子之间的结合或解离与二者之间的能垒有关,解离能垒远大于结合能垒,引起更多Na+聚集在极性头周围而只有少数Na+存在于溶液中;无论气液还是固液界面,极性头均伸向水相,与水分子形成不同类型的氢键.模拟表明,分子动力学方法可以作为实验的一种补充,为实验提供必要的微观结构信息.

We performed molecular dynamics （MD） simulations to investigate anionic surfactant sodium dodecyl benzene sulfonate （SDBS） adsorption onto a silica surface from solution. Various water phases of different thickness were constructed to investigate the difference between the solid/liquid and the air/liquid interface. We found that surfactant molecules adsorbed on silica surfaces within a short simulation time and they formed a surfactant layer via an interaction between the hydrophobic alkyl chain and the SiO2 surface. With an increase in water phase, one hemi- cylindrical micelle with a hydrophobic core formed on the SiO2 surface when a large amount of surfactant molecules adsorbed. The potential of mean force potential between the polar head of the surfactant and Na ~ ions or water molecules shows that the dissociation energy barrier is much larger than the combination energy barrier leading to more Na~ ions gathering around the polar head and fewer Na~ in solution. SDBS and water molecules can form complexes through H-bonding at the air/liquid or solid/liquid interface. Simulation results show that molecular dynamics can be used as an adjunct and can provide necessary information for microstructural property experiments.