阴离子表面活性剂与阳离子的相互作用 曹绪龙 1,2 吕 凯 2 崔晓红 1 石 静 1 苑世领 2, * ( 1 中国石化胜利油田分公司地质科学研究院, 山东 东营 257015; 2 山东大学胶体与界面化学教育部重点实验室, 济南 250100) 摘要: 用密度泛函 理论, 在 B3LYP/6 鄄31G 水平上, 对十二烷基磺酸盐和羧酸盐阴离子表面活性剂与阳离子 (Na + , Ca 2+ , Mg 2+ )形成的离子对进行结构优化, 从分子水平上研究表面活性剂与阳离子之间的相互作用. 计算结果 表明: 磺酸盐和羧酸盐表面活性剂均采用 2颐1 型, 即极性头中两个氧原子与阳离子发生稳定结合; 在与阳离子结 合之前, 表面活性剂分子上的 琢鄄亚甲基带有明显的负电荷, 因此将其归为极性头; 但在阳离子电荷诱导下, 琢鄄亚 甲基转而带有部分弱正电荷, 使极性头范围缩小. 计算也发现, 表面活性剂尾链带有弱正电荷, 使胶束内核带有 了部分极性, 利于表面活性剂在溶液中的聚集, 此种极性介于烷烃油相和水相的极性之间. 关键词: 密度泛函理论; 阴离子表面活性剂; 相互作用; 胶束; 电荷 中图分类号: O641; O648 Interactions between Anionic Surfactants and Cations CAO Xu鄄Long 1,2 L譈 Kai 2 CUI Xiao鄄Hong 1 SHI Jing 1 YUAN Shi鄄Ling 2,* ( 1 Institute o f Geology Science, Shengli Oilfield Ltd. Co., Dongying 257015, Shandong Province, P. R. China ; 2 Key Laboratory of Colloid and Int erface Chemistry, Mi nistry of Educatio n, Shandong Universit y, Jinan 250100, P. R. China ) Abstract : The ion鄄pairs of the anionic surfactants (dodecyl sulfonate, dodecyl carboxylate) and the cations (Na + , Ca 2+ , Mg 2+ ) were optimized using density functional theory (DFT) at the B3LY/6 鄄31G level and the interaction between the surfactants and ions were studied at the molecular level. The results showed that: i) a 2颐1 type of ion鄄pair was formed in which two oxygen atoms from the polar group in the surfactant bound with one ion; ii) the 琢鄄methylene nearest the headgroup should be classified as the part of the polar head because of its negative charge before ion bonding; iii) the charge of the 琢鄄methylene group can be converted from a weak negative into a weak positive charge by the cations, which decreased the effect of the polar headgroup. This calculation also showed that the tail chain had a weak positive charge in the micelle resulting in the core of the micelle having polarity. This core polarity of the micelle is somewher e betwe en the oil phase polari ty and the wate r phase polarit y, which favor s surf actan t aggr egati on in solution. Key Words: Densi ty functional theo ry; Anionic surf acta nt; Inte racti on; Mice lles ; Charg e [Article] www.whxb.pku.edu.cn 物理化学学报(Wuli Huaxue Xuebao) Acta Phys. 鄄Chim. Sin., 2010, 26(7): 1959-1964 表面活性剂的双亲性质 体现在不同的亲水和 疏水结构单元的组合, 在溶液中更易形成疏水核心, 这是从表面活性剂的分子结构特点进行的推测. 目 前已经有原子力显微镜等实验 手段观察到了分子 聚集形成的囊泡结构 [1-3] , 也可借助分子动力学等模 拟方法对表面活性剂在溶液或界面上的聚集行为预 测 [4-8] , 但是二者均不能从分子水平上给出表面活性 剂在溶液中聚集的结构变化以及与反离子之间形成 离子对的实质. 由于表面活性剂分子结构复杂, 一般 由数十个甚至上百个原子组成, 且一端亲油一端亲 July Received: January 29, 2010; Revised: April 21, 2010; Published on Web: May 18, 2010. 鄢 Corresponding author. Email: [email protected]; Tel: +86 鄄531鄄88365896. The project was supported by the National Natural Science Foundation of China (20873074) and the PetroChina Innovation Foundation. 国家自然科学基金(20873074)和中国石油科技创新基金资助项目 鬁 Editorial office of Acta Physico鄄Chimica Sinica 1959
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8/6/2019 2010 Interactions Between Anionic Surf Act Ants and Cations
Interactions between Anionic Surfactants and Cations
CAO Xu鄄Long1,2 L譈 Kai2 CUI Xiao鄄Hong1 SHI Jing1 YUAN Shi鄄Ling2,*
(1 Institute of Geology Science, Shengli Oilfield Ltd. Co., Dongying 257015, Shandong Province, P. R. China;2
Key Laboratory of Colloid and Interface Chemistry, Ministry of Education, Shandong University, Jinan 250100, P. R. China)
Abstract: The ion鄄pairs of the anionic surfactants (dodecyl sulfonate, dodecyl carboxylate) and the cations (Na +,
Ca2+, Mg2+) were optimized using density functional theory (DFT) at the B3LY/6鄄31G level and the interaction between
the surfactants and ions were studied at the molecular level. The results showed that: i) a 2 颐1 type of ion鄄pair was
formed in which two oxygen atoms from the polar group in the surfactant bound with one ion; ii) the 琢鄄methylene
nearest the headgroup should be classified as the part of the polar head because of its negative charge before ion
bonding; iii) the charge of the 琢鄄methylene group can be converted from a weak negative into a weak positive charge
by the cations, which decreased the effect of the polar headgroup. This calculation also showed that the tail chain had a
weak positive charge in the micelle resulting in the core of the micelle having polarity. This core polarity of the micelle
is somewhere between the oil phase polarity and the water phase polarity, which favors surfactant aggregation in
solution.
Key Words: Density functional theory; Anionic surfactant; Interaction; Micelles; Charge
[Article] www.whxb.pku.edu.cn
物理化学学报(Wuli Huaxue Xuebao)
Acta Phys. 鄄Chim. Sin., 2010, 26(7):1959-1964
表面活性剂的双亲性质 体现在不同的亲水和
疏水结构单元的组合, 在溶液中更易形成疏水核心,
这是从表面活性剂的分子结构特点进行的推测.目
前已经有原子力显微镜等实验手段观察到了分子
聚集形成的囊泡结构[1-3],也可借助分子动力学等模
拟方法对表面活性剂在溶液或界面上的聚集行为预
测[4-8],但是二者均不能从分子水平上给出表面活性
剂在溶液中聚集的结构变化以及与反离子之间形成
离子对的实质.由于表面活性剂分子结构复杂,一般
由数十个甚至上百个原子组成,且一端亲油一端亲
July
Received: January 29, 2010; Revised: April 21, 2010; Published on Web: May 18, 2010.
鄢
Corresponding author. Email: [email protected]; Tel: +86鄄531鄄88365896.The project was supported by the National Natural Science Foundation of China (20873074) and the PetroChina Innovation Foundation.
国家自然科学基金(20873074)和中国石油科技创新基金资助项目
鬁 Editorial office of Acta Physico鄄Chimica Sinica
1959
8/6/2019 2010 Interactions Between Anionic Surf Act Ants and Cations
Table 1 Geometry parameters and binding energies (驻 E) of ion鄄pairs between surfactant and cation ion
i) When the third bond is 0.1 nm longer than the first two bonds, we define that this bond is the different type from the formers. For example, as forsodium dodecyl sulfate (SDS) and Na+ pair, the third RO鄄ion=0.417 nm which is longer than the first two bonds (0.237 nm), thus they are not of the same
type. ii) In the table, the configuration with marked“*”data are the most optimal configuration.
图 2 钠离子与磺酸盐极性头可能的结合方式以及优化结果
Fig.2 Possible binding modes and optimization
structures between sulfonate polar head and Na+ ion