Structure, Interfacial Properties, and Dynamics of the Sodium Alkyl Sulfate Type Surfactant Monolayer at the Water/Trichloroethylene Interface: A Molecular Dynamics Simulation Study
Structure, Interfacial Properties, and Dynamics of the Sodium Alkyl Sulfate Type Surfactant Monolayer at the Water/Trichloroethylene Interface: A Molecular Dynamics Simulation Study
复制标题
烷基硫酸钠型表面活性剂单分子层在水/三氯乙烯界面的结构、界面性质和动力学：分子动力学模拟研究
DOI：
10.1021/jp100868p
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发表时间：
2010-05-20
影响因子：
3.3
通讯作者：
Guo, Hong-Xia
中科院分区：
文献类型：
--
作者：
Shi, Wen-Xiong;Guo, Hong-Xia
在这项工作中，我们进行了一系列的分子动力学（MD）模拟烷基硫酸钠（SDS型）表面活性剂单分子膜在水/三氯乙烯（TCE）界面的类别。使用三种单独的尾长SID型分子。我们研究了表面活性剂链的构象（即，堆积、取向和顺序），界面性质（即，界面厚度、界面张力、面积压缩性和弯曲模量）、它们对链长的依赖性和每个表面活性剂链的平均面积。我们还研究了在亚稳制度的负表面张力与崩溃的表面活性剂单层的行为。模拟清楚地表明，非常稀的单分子层很好地描述为二维气体。随着界面活性剂覆盖率的增加，单分子膜处于液体膨胀（LE）相。表面活性剂覆盖率越高，界面处的表面活性剂尾部越直、越有序、越厚。同时，长尾体系的界面张力总是低于短尾体系。在LE阶段，面积压缩模量和弯曲模量随着尾长的增加而增加。随着分子面积的进一步减小，具有大的负表面张力的单分子膜变得不稳定。我们的模拟表明，屈曲的单层是动态的性质作为一个响应的机械不稳定性。从屈曲到出芽的进一步转化途径可以通过弯曲模量来控制，弯曲模量关键地取决于尾部长度和界面表面活性剂覆盖度。在每个分子给定的面积下，短尾链使单层更柔软，并且出芽过程变得更可能。对于过饱和的较软的SDS单分子层，崩溃过渡是由单分子层的屈曲，其次主要是由出芽和脱离的纳米级溶胀胶束从单分子层。尽管在空气/水界面处的单层坍塌的大量的研究，据我们所知，表面活性剂从液-液界面到溶胀胶束聚集体的转化，如这里所描述的，还没有在文献中报道。
In this work, we perform a series of molecular dynamics (MD) simulations on the category of sodium alkyl sulfate (SDS-type) surfactant monolayers at the water/trichloroethylene (TCE) interface. Three separate tail-length SIDS-type molecules are used. We investigate the conformation of surfactant chain (i.e., packing, orientation, and order), interfacial properties (i.e., interfacial thickness, interfacial tension, area compressibility, and bending modulus), their dependence on the chain length, and the average area per surfactant chain. We also examine the behavior of the surfactant monolayer in the metastable regime of negative surface tension with reference to collapse. The simulation has clearly shown that the very dilute monolayer is well described as a two-dimensional gas. With the increase of interfacial surfactant coverage, the monolayer is in the liquid-expanded (LE) phase. The surfactant tails at the interface become straighter, more ordered, and thicker at higher surfactant coverage. At the same time, interfacial tension of long-tail systems is always lower than that of short-tail systems. In the LE phase, the area compressibility modulus and the bending modulus increase with an increase in tail length. With a further decrease in molecular areas, the monolayer with large negative surface tension becomes unstable. Our simulations show that buckling of the monolayers is of dynamic nature as a response to mechanical instability. The further transformation pathway from buckling to bud can be controlled by the bending modulus, which depends crucially on the tail length and interfacial surfactant coverage. At a given area per molecule, the short tail chain makes the monolayer softer, and the budding process becomes more probable. For the supersaturated softer SDS monolayer, the collapse transition is initiated by the buckling of monolayers, followed primarily by budding and detachment of the nanoscale swollen micelle from the monolayer. Despite a number of extensive studies of monolayer collapse at the air/water interface, to our knowledge the conversion of surfactants from the liquid-liquid interface to swollen micellar aggregates as described here has not been reported in the literature.