Beijing National Laboratory for Molecular Sciences (BNLMS), State Key Laboratory of Polymer Science and Engineering, Joint Chinese Academy of Sciences, Beijing, China.
J Phys Chem B. 2011 Apr 28;115(16):4645-53. doi: 10.1021/jp108433k. Epub 2011 Apr 6.
The foam stability performance of a mixture surfactant system with and without calcium ions, including linear alkylbenzenesulfonate (LAS) and sodium dodecyl sulfate (SDS), has been studied by molecular dynamics. Microscopic interaction analysis reveals that the average binding number (ABN) indicates the population of interaction configurations at short distance (∼0.23 nm), ABN = 0.88 for the mixture system that is larger than that of SDS (0.08) and smaller than that of LAS (1.00). ABN of the mixture 0.88 in between is consistent with experimental observations; the performance of the mixture becomes worse than that of LAS and better than that of SDS on the foam stability influenced by calcium ions. In the present anionic system, the fraction of free calcium ions, X(f), in the film system was obtained. If X(f) is in the high calcium ion zone (X(f) > 0.5), the foam stability performance appears to be considerably impacted by calcium ions. In the present study, we validated the variable of tail mass out of water film, W, is an indicator of foam stability in a system without Ca(2+). LAS+SDS mixture system has lower W value than the LAS single system, corresponding to its experimental observation on more stable foam film. Results show that a maximum of W value occurs before reaching the critical thickness for each investigated system. This was probably due to structural transition of the surfactant film system.
采用分子动力学研究了含有和不含有钙离子的混合表面活性剂体系（包括直链烷基苯磺酸钠（LAS）和十二烷基硫酸钠（SDS））的泡沫稳定性性能。微观相互作用分析表明，平均结合数（ABN）表示短距离（约 0.23nm）的相互作用构型的种群，混合物体系的 ABN=0.88 大于 SDS（0.08）而小于 LAS（1.00）。混合物的 ABN 为 0.88 介于两者之间，与实验观察结果一致；在钙离子影响泡沫稳定性方面，混合物的性能比 LAS 差，比 SDS 好。在本阴离子体系中，获得了膜体系中游离钙离子分数 X(f)。如果 X(f)处于高钙离子区（X(f)＞0.5），则泡沫稳定性性能受到钙离子的显著影响。在本研究中，我们验证了出水面膜尾质量变量 W 是无 Ca(2+)体系中泡沫稳定性的一个指标。LAS+SDS 混合体系的 W 值低于 LAS 单一体系，这对应于其在更稳定的泡沫膜上的实验观察。结果表明，对于每个研究体系，在达到临界厚度之前，W 值达到最大值。这可能是由于表面活性剂膜体系的结构转变。
