钠蒙脱土晶层间水分子结构分子动力学模拟

对晶层间不同含水量的蒙脱土-水-离子体系以及NaCl水溶液进行分子动力学模拟，并比较了矿物晶层间水分子及离子特性与水溶液中的差别。模拟结果表明：层间补偿阳离子受蒙脱矿物同晶置换位置影响，而层间水分子则与四面体氧原子形成氢键配位，沿矿物表面定向排列；层间水分子及离子受黏土矿物几何限制及表面电荷的影响，其沿zz方向的扩散系数很小，且总扩散系数也要小于NaCl水溶液；层间水分子中氢、氧原子间及其与钠离子间的径向分布函数峰值强度要高于水溶液，也说明了晶层间水的聚合程度更高。以上结果定量描绘了晶层间水分子的结构形态，同时也充分说明了晶层间水分子的结构明显不同于自由水，为下一步研究黏土的高压力学特性奠定了基础。

Molecular dynamic simulation of interlayer water structure in Na-montmorillonite

The montmorillonite mineral with different water contents and the sodium chloride aqueous solution were investigated by molecular dynamics simulation，and the different characteristics of water and ion within these two systems were compared.The simulation results reveal that the locations of interlayer counterions are influenced by the ismorphous substitution of mineral，and the interlayer water molecules form hydrogen bonds with the tetrahedron oxygen atoms，oriented along the mineral surface.By the way，the self diffusion coefficient of water molecules and counterions in the interlayer is smaller than those in aqueous solution，especially in the zz direction.But the peak intensity of radial distribution functions between oxygen/hydrogen and sodium and inter water atoms in montmorillonite system is higher than those in bulk solution，which means that the degree of integration of water molecules within the crystal layers is higher than the aqueous solution.All of these quantitative results show that the structure properties of interlayer water are significantly different from the free water molecules，and this study laid the foundation for the next step to study the high pressure mechanical properties of saturated clay.