School of Chemistry and Chemical Engineering and Key Laboratory for Thin Film and Microfabrication, Ministry of Education, Shanghai Jiao Tong University , Shanghai 200240, China.
Langmuir. 2013 Sep 10;29(36):11300-9. doi: 10.1021/la402255m. Epub 2013 Aug 27.
The stability of Newton black films (NBFs) under lateral mechanical stretch was investigated by nonequilibrium molecular dynamics (NEMD) simulations using force field parameters validated by accurate prediction of surface tensions. The applied strains accelerated film ruptures, enabling efficient measurements of the critical thicknesses of the films. Two representative surfactants, sodium dodecyl sulfate (SDS) for ionic surfactant and pentaethylene glycol monododecyl ether (C12EO5H) for nonionic surfactant, were investigated and compared. The predicted critical thickness of C12EO5H-coated film is smaller than that of the SDS-coated film, which is consistent with previously reported experimental observations. Our simulation results show that while the two surfactant-coated films exhibit similar dynamic properties attributed to the Marangoni-Gibbs effect, their surface structural characteristics are quite different. Consequently the two films demonstrate distinct rupture mechanisms in which rupture starts at uncovered water domains in the SDS-coated film, but at lateral surfactant/water interfaces in the C12EO5H-coated film. Our findings provide new insights into the stabilization mechanisms of NBFs and will facilitate the design and development of new films with improved properties.
采用经准确表面张力预测验证的力场参数，通过非平衡分子动力学（NEMD）模拟研究了牛顿黑膜（NBF）在横向机械拉伸下的稳定性。施加的应变加速了膜的破裂，从而能够有效地测量膜的临界厚度。研究并比较了两种代表性的表面活性剂，离子表面活性剂十二烷基硫酸钠（SDS）和非离子表面活性剂五乙二醇单十二醚（C12EO5H）。预测的 C12EO5H 涂层膜的临界厚度小于 SDS 涂层膜的临界厚度，这与先前报道的实验观察结果一致。我们的模拟结果表明，尽管两种表面活性剂涂层膜表现出相似的动态特性归因于 Marangoni-Gibbs 效应，但它们的表面结构特征却大不相同。因此，这两种膜表现出不同的破裂机制，在 SDS 涂层膜中破裂始于未覆盖水的区域，而在 C12EO5H 涂层膜中破裂始于侧向表面活性剂/水界面。我们的研究结果为 NBF 的稳定机制提供了新的见解，并将有助于设计和开发具有改进性能的新型薄膜。
