Yang Xue-Dan, Chen Wei, Ren Ying, Chu Liang-Yin
School of Chemical Engineering, Sichuan University, Chengdu, Sichuan 610065, China.
State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu, Sichuan 610065, China.
Langmuir. 2022 Jan 25;38(3):1277-1286. doi: 10.1021/acs.langmuir.1c03205. Epub 2022 Jan 11.
It is well-known that surfactants tend to aggregate into clusters or micelles in aqueous solutions due to their special structures, and it is difficult for the surfactant molecules involved in the aggregation to move spontaneously to the oil-water interface. In this article, we developed a new grand-canonical molecular dynamics (GCMD) model to predict the saturated adsorption amount of surfactant with constant concentration of surfactant molecules in the bulk phase, which can prevent surfactants aggregating in the bulk phase and get the atomic details of the interfacial structural change with increase of the adsorption amount through a single GCMD run. The adsorption of anionic surfactant sodium dodecyl sulfate (SDS) at the heptane-water interface was studied to validate the model. The saturated adsorption amount obtained from the GCMD simulation is consistent with the experimental results. The adsorption kinetics of SDS molecules during the simulation can be divided into three stages: linear adsorption stage, transition adsorption stage, and dynamic equilibrium stage. We also carried out equilibrium molecular dynamics (EMD) simulations to compare with GCMD simulation. This GCMD model can effectively reduce the simulation time with correct prediction of the interfacial saturation adsorption. We believe the GCMD method could be especially helpful for the computational study of surfactant adsorption under complex environments or emulsion systems with the adsorption of multiple types of surfactants.
众所周知，由于其特殊结构，表面活性剂在水溶液中倾向于聚集成簇或胶束，并且参与聚集的表面活性剂分子很难自发地移动到油水界面。在本文中，我们开发了一种新的巨正则分子动力学（GCMD）模型，以预测在本体相中表面活性剂分子浓度恒定情况下表面活性剂的饱和吸附量，该模型可以防止表面活性剂在本体相中聚集，并通过单次GCMD运行获得随着吸附量增加界面结构变化的原子细节。研究了阴离子表面活性剂十二烷基硫酸钠（SDS）在庚烷 - 水界面的吸附以验证该模型。从GCMD模拟获得的饱和吸附量与实验结果一致。模拟过程中SDS分子的吸附动力学可分为三个阶段：线性吸附阶段、过渡吸附阶段和动态平衡阶段。我们还进行了平衡分子动力学（EMD）模拟以与GCMD模拟进行比较。该GCMD模型可以在正确预测界面饱和吸附的情况下有效减少模拟时间。我们相信GCMD方法对于复杂环境下表面活性剂吸附或多种类型表面活性剂吸附的乳液体系的计算研究可能特别有帮助。
