University of Applied Sciences, The iCIMSI Research Institute, Galleria 2, CH-6928 Manno, Switzerland.
J Chem Phys. 2012 Sep 7;137(9):094904. doi: 10.1063/1.4747827.
We report on a molecular dynamics investigation of the wetting properties of graphitic surfaces by various solutions at concentrations 1-8 wt. % of commercially available non-ionic surfactants with long hydrophilic chains, linear or T-shaped. These are surfactants of length up to 160 Å. It turns out that molecular dynamics simulations of such systems ask for a number of solvent particles that can be reached without seriously compromising computational efficiency only by employing a coarse-grained model. The MARTINI force field with polarizable water offers a framework particularly suited for the parameterization of our systems. In general, its advantages over other coarse-grained models are the possibility to explore faster long time scales and the wider range of applicability. Although the accuracy is sometimes put under question, the results for the wetting properties by pure water are in good agreement with those for the corresponding atomistic systems and theoretical predictions. On the other hand, the bulk properties of various aqueous surfactant solutions indicate that the micellar formation process is too strong. For this reason, a typical experimental configuration is better approached by preparing the droplets with the surfactants arranged in the initial state in the vicinity of contact line. Cross-comparisons are possible and illuminating, but equilibrium contact angles as obtained from simulations overestimate the experimental results. Nevertheless, our findings can provide guidelines for the preliminary assessment and screening of surfactants. Most importantly, it is found that the wetting properties mainly depend on the length and apolarity of the hydrophobic tail, for linear surfactants, and the length of the hydrophilic headgroup for T-shaped surfactants. Moreover, the T-shaped topology appears to favor the adsorption of surfactants onto the graphitic surface and faster spreading.
我们报告了一个分子动力学研究，研究了各种浓度为 1-8wt%的市售非离子表面活性剂在石墨表面的润湿性质，这些表面活性剂具有长亲水头基，线性或 T 形。这些表面活性剂的长度可达 160Å。事实证明，只有使用粗粒化模型，才能在不严重影响计算效率的情况下，达到模拟此类系统所需的溶剂粒子数量。带有极化水的 MARTINI 力场为我们的系统提供了一个特别适合参数化的框架。一般来说，它相对于其他粗粒化模型的优势在于能够探索更快的长时间尺度和更广泛的适用性。尽管准确性有时受到质疑，但纯水的润湿性质的结果与相应的原子系统和理论预测的结果非常吻合。另一方面，各种水基表面活性剂溶液的体相性质表明胶束形成过程太强。出于这个原因，通过在初始状态下在接触线附近安排表面活性剂来制备液滴是一种更好的典型实验配置。交叉比较是可能的和有启发性的，但模拟得到的平衡接触角高估了实验结果。尽管如此，我们的发现可以为表面活性剂的初步评估和筛选提供指导。最重要的是，发现润湿性质主要取决于线性表面活性剂的疏水尾的长度和非极性，以及 T 形表面活性剂的亲水头部基团的长度。此外，T 形拓扑似乎有利于表面活性剂在石墨表面上的吸附和更快的铺展。
