Adsorption Free Energies of Imidazolinium-Type Surfactants in Infinite Dilution and in Micellar State on Gold Surface
Adsorption Free Energies of Imidazolinium-Type Surfactants in Infinite Dilution and in Micellar State on Gold Surface
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无限稀释和胶束态咪唑啉鎓型表面活性剂在金表面的吸附自由能
DOI：
10.1021/acs.jpcb.8b02358
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
Sharma, Sumit
中科院分区：
文献类型：
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作者：
Kurapati, Yathish;Sharma, Sumit
我们报告了使用全原子分子动力学模拟研究的不同聚集状态的咪唑啉鎓型表面活性剂分子在金属-水界面上的吸附行为。已经考虑了具有两种不同烷基尾长度、10-碳和17-碳尾（下文分别称为imid-10和imid-17）的表面活性剂分子。浸入水中的金原子的六层面心立方晶格代表金属-水界面。我们的模拟表明，在无限稀释中，两种类型的表面活性剂分子都强烈吸附在金属-水界面上，其烷基尾部平行于表面。这种吸附是通过吸附自由能约为 30kBT 的无势垒转变发生的，并且被发现是焓驱动的且熵不利。另一方面，由于胶束周围存在由反离子及其溶剂化层组成的大“电晕”，表面活性剂胶束会在 50-60 Å 的距离内经历与金属表面的长程排斥。表面活性剂胶束的吸附自由能垒为~13-16kBT，这与金属表面吸附水的去除有关。胶束在本体水相中是热力学稳定的，并且吸附的胶束状态仅是亚稳态的。
We report adsorption behavior of imidazolinium-type surfactant molecules in different aggregation states on metal–water interfaces studied using all-atom molecular dynamics simulations. Surfactant molecules with two different alkyl tail lengths, a 10-carbon and a 17-carbon tail (henceforth referred to as imid-10 and imid-17, respectively), have been considered. Six layers of face-centered cubic lattice of gold atoms submerged in water represent the metal–water interface. Our simulations reveal that, in infinite dilution, both types of surfactant molecules strongly adsorb onto the metal–water interface in a configuration with their alkyl tail lying parallel to the surface. This adsorption occurs through a barrierless transition with an adsorption free energy of ∼30kBTand is found to be enthalpically driven and entropically unfavorable. Surfactant micelles, on the other hand, experience a long-range repulsion from the metal surface at distances as large as 50–60 Å due to the presence of a large “corona” around the micelles that comprises counterions and their solvation layer. Surfactant micelles have an adsorption free energy barrier of ∼13–16kBT, which is associated with the removal of adsorbed water from the metal surface. Micelles are thermodynamically stable in the bulk aqueous phase, and the adsorbed micellar state is only metastable.