基于分子动力学模拟的钙基蒙脱石表面润湿性研究

蒙脱石作为土体中主要的黏土矿物之一，其表面的润湿性对土体膨胀机制有着重要的影响。目前已有大量的研究对蒙脱石的亲水性进行了分析，但原子尺度的润湿机制仍有待探究。以钙基蒙脱石为例，基于分子动力学模拟计算了水分子在其表面的接触角，并结合原子的径向分布函数和密度分布特征分析了水分子在钙基蒙脱石表面的润湿性。结果表明：在300 K温度下，水分子在钙基蒙脱石表面的接触角为18.03°，计算结果与前人的试验数据一致性较好；Ca-O水和Ca-H水的径向分布函数都呈现出双峰特性，而Ca-O水的第一峰位更早出现，说明水中的氧更倾向于与钙离子结合形成水合钙离子；在表面离子产生的静电场作用的诱导下，表面水中的氧原子密度分布曲线呈现多个明显的峰，形成了有序的水化分层结构，进而导致蒙脱石表面呈现出明显的亲水性。研究结果可为进一步阐明蒙脱石吸水后引发的土体膨胀破坏和水土流失等现象提供理论依据。

Surface Wettability of Ca-montmorillonite Based on Molecular Dynamics Simulation

As one of the main clay minerals in the soil, the wettability of the montmorillonite surface has an important influence on the soil expansion mechanism. A large number of studies are conducted to analyze the hydrophilicity of montmorillonite, but the wetting mechanism at the atomic scale remains to be explored. In order to explain the hydrophilic mechanism of Ca-montmorillonite surface from the atomic scale, taking Ca-montmorillonite as an example, the contact angle of water molecules on the surface was calculated based on molecular dynamics simulation, and the wettability of water molecules on the surface of Ca-montmorillonite was analyzed combined with the radial distribution functions (RDFs) and density profile characteristics of atoms. The results show that: At 300 K, the contact angle of water molecules on the surface of Ca-montmorillonite is 18.03°, and the calculated results are in good agreement with previous experimental data; The radial distribution functions of Ca-Owater and Ca-Hwater both show bimodal characteristics, while the first peak position of Ca-Owater appears earlier, indicating that oxygen in water is more inclined to combine with calcium ions to form hydrated calcium ions; Under the induction of the electrostatic field generated by the surface ions, the oxygen atomic density profile curve in the surface water presents multiple obvious peaks, forming an ordered hydration layered structure, which in turn leads to the apparent hydrophilicity of the surface of montmorillonite. The research results can provide a theoretical basis for further clarification of soil expansion failure and soil erosion caused by montmorillonite absorbing water.