Molecular modeling of initiation of interlayer swelling in Na-montmorillonite expansive clay
Molecular modeling of initiation of interlayer swelling in Na-montmorillonite expansive clay
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DOI：
10.1139/cgj-2014-0309
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发表时间：
2015-09-01
影响因子：
3.6
通讯作者：
Katti, Kalpana S.
中科院分区：
文献类型：
--
作者：
Katti, Dinesh R.;Srinivasamurthy, Lakshmikanth;Katti, Kalpana S.
世界上许多地方都有膨胀土。这些粘土的主要成分是矿物蒙脱石。粘土、阳离子和水之间的分子相互作用在膨胀中起重要作用。建立了钠蒙脱土的分子模型，并用分子动力学方法进行了溶剂化研究。分子轨迹、构象和相互作用能的分析揭示了引发层间膨胀的关键机制。在最初干燥的夹层中，由于Na离子和粘土片之间强烈的吸引力相互作用，夹层坍塌。氧原子的范德瓦尔斯（vdW）半径进一步减小了可用的间距，从而阻止水分子进入中间层。此外，人们还发现，当粘土稍微水化时，水分子可以流入夹层。水分子在层间的速度在不同的时间间隔内，并且速度随时间而减小。模拟结果表明，Na离子与水分子之间具有较强的相互吸引作用，对于吸引水分子进入夹层并引发溶胀具有重要作用。随后，水化壳形成后，水分子继续流动，可能通过氢键网络。这些研究为肿胀开始时的分子机制提供了清晰的见解。
Expansive soils are found in many parts of the world. A major constituent of these clays is the mineral montmorillonite. Molecular interactions between clay, cations, and water play an important role in swelling. Molecular models of Na-montmorillonite clay are constructed, and solvation studies are conducted using molecular dynamics. Analysis of molecular trajectories, conformations, and interaction energies reveal key mechanisms that initiate interlayer swelling. In the initially dry interlayer, the interlayer collapses due to strong attractive interactions between Na ions and clay sheets. The van der Waals (vdW) radii of the oxygen atoms further reduce available spacing, thus preventing water molecules from entering the interlayer. Further, it was found that clays, when slightly hydrated, allowed flow of water molecules into the interlayer. The speed of water molecules in the interlayer is found at various time intervals, and the speed decreases with time. The simulations elucidate that Na ions have strong attractive interactions with water molecules and are important initially for attracting water molecules into the interlayer and initiate swelling. Subsequently, after the formation of the hydration shell, flow of water molecules continues, potentially through the hydrogen bond network. These studies provide a clear insight into the molecular mechanisms at the beginning of swelling.