STFC Hartree Centre, Scitech Daresbury , Warrington WA4 4AD , United Kingdom.
Ferrante Scientific Ltd. , 5 Croft Lane , Bromborough CH62 2BX , United Kingdom.
J Chem Theory Comput. 2018 May 8;14(5):2633-2643. doi: 10.1021/acs.jctc.8b00075. Epub 2018 Apr 13.
We use dissipative particle dynamics (DPD) to study micelle formation in alkyl sulfate surfactants, with alkyl chain lengths ranging from 6 to 12 carbon atoms. We extend our recent DPD force field [ J. Chem. Phys. 2017 , 147 , 094503 ] to include a charged sulfate chemical group and aqueous sodium ions. With this model, we achieve good agreement with the experimentally reported critical micelle concentrations (CMCs) and can match the trend in mean aggregation numbers versus alkyl chain length. We determine the CMC by fitting a charged pseudophase model to the dependence of the free surfactant on the total surfactant concentration above the CMC and compare it with a direct operational definition of the CMC as the point at which half of the surfactant is classed as micellar and half as monomers and submicellar aggregates. We find that the latter provides the best agreement with experimental results. Finally, with the same model, we are able to observe the sphere-to-rod morphological transition for sodium dodecyl sulfate (SDS) micelles and determine that it corresponds to SDS concentrations in the region of 300-500 mM.
我们使用耗散粒子动力学（DPD）来研究烷基硫酸盐表面活性剂中的胶束形成，烷基链长从 6 到 12 个碳原子不等。我们扩展了我们最近的 DPD 力场[J. Chem. Phys. 2017, 147, 094503]，以包括带电荷的硫酸盐化学基团和水合钠离子。通过该模型，我们实现了与实验报道的临界胶束浓度（CMC）的良好一致性，并能够匹配平均聚集数与烷基链长的趋势。我们通过将带电伪相模型拟合到 CMC 以上的总表面活性剂浓度对游离表面活性剂的依赖性来确定 CMC，并将其与 CMC 的直接操作定义进行比较，即表面活性剂的一半被归类为胶束，另一半为单体和亚胶束的点。我们发现后一种方法与实验结果的一致性更好。最后，我们使用相同的模型，能够观察到十二烷基硫酸钠（SDS）胶束的球到棒形态转变，并确定其对应于 SDS 浓度在 300-500mM 的区域。
