Abstract Montmorillonite is the principal constituent of many expansive soils. The swelling of expansive clays upon hydration can cause significant distress to infrastructure. On the other hand, the swelling characteristics lead to many beneficial applications of these clays, such as barrier materials and in nanocomposites. The montmorillonite hierarchical structure plays a vital role in the swelling of expansive clays. The hierarchical structure of montmorillonite consists of four levels, clay mineral layers, tactoids, aggregates, and assembly of aggregates. The clay tactoid is considered as the fundamental clay particle, which consists of several clay mineral layers stacked in the Z direction. We report here for the first time a molecular mechanics study of the clay tactoid. The molecular model of sodium-montmorillonite (Na-Mt) tactoid was built, and its mechanical properties were evaluated using Molecular Dynamics (MD) and Steered Molecular Dynamics (SMD) simulations. The mechanical response of Na-Mt tactoid was evaluated under compression, tension, and shear. Compression tests revealed a short linear characteristic with a compression modulus of 125 GPa followed by a nonlinear portion with increasing modulus approaching 640 GPa, which is the modulus of a single clay mineral layer. The tensile pulling of the tactoid also indicated an influence of the tactoid nanostructure with the influence of multiple neighboring layers of tactoid. The shearing simulations indicated first a mechanical response with a modulus of 10 GPa ending with locking of interlayer cations into tetrahedral cavities followed by small displacements exhibiting a modulus of 70 GPa. All of the mechanical behaviors were related to the evaluated interaction energies between clays and cations during loading. These studies elucidated key mechanisms of swelling clay tactoid response to loading.

中文翻译：

---

压缩、拉伸和剪切作用下膨胀粘土类晶团的分子力学

摘要 蒙脱石是许多膨胀土的主要成分。膨胀粘土在水合作用时的膨胀会对基础设施造成严重破坏。另一方面，溶胀特性导致这些粘土的许多有益应用，例如阻隔材料和纳米复合材料。蒙脱石的分级结构在膨胀粘土的膨胀中起着至关重要的作用。蒙脱石的层级结构由粘土矿物层、晶状体、聚集体和聚集体集合四个层次组成。粘土tactoid被认为是基本的粘土颗粒，它由沿Z方向堆叠的几个粘土矿物层组成。我们在这里首次报告了粘土类晶状体的分子力学研究。建立了钠-蒙脱石（Na-Mt）tactoid的分子模型，并使用分子动力学 (MD) 和转向分子动力学 (SMD) 模拟评估其机械性能。在压缩、拉伸和剪切下评估 Na-Mt tactoid 的机械响应。压缩测试揭示了一个短线性特征，压缩模量为 125 GPa，随后是非线性部分，模量增加接近 640 GPa，这是单个粘土矿物层的模量。tactoid 的拉伸拉伸也表明 tactoid 纳米结构的影响与多个相邻 tactoid 层的影响。剪切模拟首先表明具有 10 GPa 模量的机械响应，最后是层间阳离子锁定到四面体腔中，然后是表现出 70 GPa 模量的小位移。所有的机械行为都与加载过程中粘土和阳离子之间评估的相互作用能有关。这些研究阐明了膨胀粘土对载荷的反应的关键机制。