【作者】 孔滨； 吴荣亮； 杨小震；

【Author】 Bin Kong,Rongliang Wu,Xiaozhen,Yang Institute of Chemistry Chinese Academy of Sciences,Beijing,100190,

【机构】 中国科学院化学研究所；

【摘要】 我们采用分子动力学模拟了具有[C₁₂H₂₅（CH₃）₂N（CH₂）_SN（CH₃）₂C₁₂H₂₅]Br₂（12-S-12,S=3,6和12）结构的gemini表面活性剂在油/水界面上的单分子膜,为了和gemini进行比较我们还模拟了十二烷基三甲基溴化铵（DTAB）的单分子膜。所谓gemini表面活性剂,它有两个亲水头基和两个疏水链,其两个头基由一条连接链相连。这类表面活性剂自发明以来引起了很多的表面科学家的关注。Gemini表面活性剂具有很低的临界胶束浓度（CMC）及特殊的聚集行为,并且由于这些特殊的性质它们在洗涤,食品及原油提纯领域有着广泛的应用。从表面活性剂及其各基团的分布发现液/液界面上其分布比水/气界面宽很多,12-3-12和12-6-12的连接链弯向疏水相的程度不高,而12-12-12的连接链倾向于弯向疏水相。表面活性剂的构象表明连接链比尾链要更加柔顺。能够表征表面活性剂结构的特征角很好地描述了表面活性剂在界面上的形态。12-3-12两个N⁺相对位置比较固定而12-6-12两个N⁺的相对位置取决于其连接链中间二面角的构象而12-12-12的两个N⁺行为比较独立。通过空间分布函数可以发现水分子和反离子倾向于共享两个相邻的甲基或亚甲基。更多还原

【Abstract】 Molecular dynamics simulations have been performed on the monolayers of dodecyltrimethylammonium bromide(DTAB) and gemini surfactants 12-S-12 with S = 3,6,and 12 at the n-heptane/water interfaces.The density profiles normal to the interface show that the distributions ofsurfactants at the liquid/liquid interface are significantly broader than those at air/water interfaces from comparisons with neutron reflection experiments and previous simulations.The spacers of 12-3-12 and 12-6-12 do not migrate much from the interface while that of 12-12-12 tends to bend into the oil phase.The conformation of the surfactants shows that the spacers are more flexible than the tails.Angles characteristic of the surfactant geometry well depict the geometry of the surfactants at the interface.The connected N+ of 12-3-12 and 12-6-12 have prominent peaks in the radial distribution functions while those of 12-12-12 have nearly the same peak with those not connected.It is also found by three dimensional spatial distribution functions that water molecules and the bromide ions prefer to be shared between the positively charged methyl or methylene groups.更多还原