钙离子对表面活性剂单层膜聚集结构的影响

采用分子动力学模拟研究了气液界面上钙离子对阴离子表面活性剂十二烷基苯磺酸钠单层膜聚集结构的影响.结果表明,单层膜结构与表面覆盖度及Ca2＋离子存在与否均有关系.Ca2＋离子能够压缩表面活性剂极性头使聚集结构排列更加紧密,均力势体现了Ca2＋离子与极性头之间的结合能力强弱,二者之间的相互作用与稳定的溶剂分离极小值有关,而Ca2＋离子需要克服一个溶剂能障才能与之发生相互作用,并引起极性头周围水分子结构的重排.模拟表明,分子动力学方法可以在分子水平上研究无机盐离子对表面活性剂单层膜水化结构的影响,解释无机盐离子在界面膜中的动力学行为.

Effect of calcium ions on the monolayer aggregates of surfactant

The effect of Ca2＋ ions on the hydration shell of sodium dodecyl sulfonate（SDSn） monolayer at vapor/liquid interface was studied using molecular dynamics simulations.The result showed that the aggregation structures relate to both the surface coverage and the calcium ions existing.Ca2＋ ions can bind to the head group to make the aggregation much more compact.The potential of mean force（PMF） between Ca2＋ and the headgroups showed that the interaction was prevented by a stabilizing solvent-separated minimum in the PMF.Among contributions to the PMF,the major repulsive interaction was due to the rearrangement of the hydration shell after the calcium ions entered into the hydration shell of the head group.The simulation showed that the method of molecular dynamics can research the effect of the inorganic ions on the monolayer of the surfactants’ hydration structure in the molecular level,and interpret the dynamic behavior of the inorganic ions on the monolayer at the Vapor/Liquid interface.