Müller Paulina, Bonthuis Douwe Jan, Miller Reinhard, Schneck Emanuel
Physics Department, Technische Universität Darmstadt, 64289 Darmstadt, Germany.
Institute of Theoretical and Computational Physics, Technische Universität Graz, 8010 Graz, Austria.
J Phys Chem B. 2021 Jan 14;125(1):406-415. doi: 10.1021/acs.jpcb.0c08615. Epub 2021 Jan 5.
Ionic surfactants are known to build up higher interfacial pressures at oil/water interfaces than at air/water interfaces for the same surfactant bulk concentration. Here, we systematically investigate this effect through atomistic molecular dynamics (MD) simulations of surfactant-loaded air/water and oil/water interfaces. Two prototypical ionic surfactants, CTAB and sodium dodecyl sulfate (SDS), are studied and found to give consistent results, which are also robust with respect to variations in the simulation force field. The simulations reproduce the experimental interfacial pressure data on a semiquantitative level and reveal that the influence of oil on the surfactants' in-plane distribution is a major contribution to the observed effect, albeit insufficient to be the sole reason. The simulations are further analyzed with regard to surfactant/oil cooperative/competitive effects that have been invoked recently as an explanation. However, the interfacial orientation of oil molecules, a presumable indicator for such behavior, is found to display changes only for high levels of surfactant coverage.
已知对于相同的表面活性剂本体浓度，离子型表面活性剂在油/水界面处比在空气/水界面处能建立更高的界面压力。在此，我们通过对负载表面活性剂的空气/水和油/水界面进行原子分子动力学（MD）模拟，系统地研究了这种效应。研究了两种典型的离子型表面活性剂，十六烷基三甲基溴化铵（CTAB）和十二烷基硫酸钠（SDS），发现它们给出了一致的结果，并且对于模拟力场的变化也具有稳健性。模拟在半定量水平上重现了实验界面压力数据，并揭示出油对表面活性剂面内分布的影响是观察到的效应的主要贡献，尽管不足以成为唯一原因。针对最近作为一种解释而提出的表面活性剂/油协同/竞争效应，对模拟进行了进一步分析。然而，发现油分子的界面取向（这种行为的一个可能指标）仅在高水平的表面活性剂覆盖下才会显示出变化。
