Shen Xinyi, Bourg Ian C
Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ 08544, USA.
Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ 08544, USA; High Meadows Environmental Institute, Princeton University, Princeton, NJ 08544, USA.
J Colloid Interface Sci. 2021 Feb 15;584:610-621. doi: 10.1016/j.jcis.2020.10.029. Epub 2020 Oct 13.
Colloidal interactions between clay nanoparticles have been studied extensively because of their strong influence on the hydrology and mechanics of many soils and sedimentary media. The predominant theory used to describe these interactions is the Derjaguin-Landau-Verwey-Overbeek (DLVO) model, a framework widely applied in colloidal and interfacial science that accurately predicts the interactions between charged surfaces across water films at distances greater than ~ 3 nm (i.e., ten water monolayers). Unfortunately, the DLVO model is inaccurate at the shorter interparticle distances that predominate in most subsurface environments. For example, it inherently cannot predict the existence of equilibrium states wherein clay particles adopt interparticle distances equal to the thickness of one, two, or three water monolayers. Molecular dynamics (MD) simulations have the potential to provide detailed information on the free energy of interaction between clay nanoparticles; however, they have only been used to examine clay swelling and aggregation at interparticle distances below 1 nm. We present the first MD simulation predictions of the free energy of interaction of smectite clay nanoparticles in the entire range of interparticle distances from the large interparticle distances where the DLVO model is accurate (>3 nm) to the short-range swelling states where non-DLVO interactions predominate (<1 nm). Our simulations examine a range of salinities (0.0 to 1.0 M NaCl) and counterion types (Na, K, Ca) and establish a detailed picture of the breakdown of the DLVO model. In particular, they confirm previous theoretical suggestions of the existence of a strong non-DLVO attraction with a range of ~ 3 nm arising from specific ion-clay Coulomb interactions in the electrical double layer.
由于黏土纳米颗粒之间的胶体相互作用对许多土壤和沉积介质的水文学和力学性质有强烈影响，因此已被广泛研究。用于描述这些相互作用的主要理论是德亚金-朗道-韦弗-奥弗贝克（DLVO）模型，这是一个在胶体和界面科学中广泛应用的框架，能准确预测带电表面在大于约3纳米（即十个水单层）的距离上通过水膜的相互作用。不幸的是，DLVO模型在大多数地下环境中占主导的较短颗粒间距离时并不准确。例如，它本质上无法预测黏土颗粒采用等于一个、两个或三个水单层厚度的颗粒间距离的平衡态的存在。分子动力学（MD）模拟有潜力提供关于黏土纳米颗粒间相互作用自由能的详细信息；然而，它们仅被用于研究颗粒间距离低于1纳米时的黏土膨胀和聚集。我们给出了蒙脱石黏土纳米颗粒在从DLVO模型准确的大颗粒间距离（>3纳米）到非DLVO相互作用占主导的短程膨胀态（<1纳米）的整个颗粒间距离范围内相互作用自由能的首个MD模拟预测。我们的模拟研究了一系列盐度（0.0至1.0 M NaCl）和抗衡离子类型（Na、K、Ca），并建立了DLVO模型失效的详细情况。特别是，它们证实了先前的理论建议，即由于电双层中特定的离子-黏土库仑相互作用，存在范围约为3纳米的强非DLVO吸引力。
