Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, Canada T6G 2G6.
Langmuir. 2011 Nov 1;27(21):12996-3007. doi: 10.1021/la2027829. Epub 2011 Sep 30.
To fundamentally understand the electrokinetic behavior of clay minerals, it is necessary to study the anisotropic surface charge properties of clay surfaces. In this study, two 2:1 layer natural minerals, talc and muscovite, were chosen as representatives of magnesium and aluminum phyllosilicate minerals, respectively. The molecularly smooth basal planes of both platy minerals were obtained by cleavage along the basal planes, while suitable edge surfaces were prepared by an ultramicrotome cutting technique. Silicon nitride atomic force microscopy tip was used as a probe to study the interaction forces between the tip and clay basal/edge surfaces in aqueous solutions of various pH values. The measured interaction force profiles between the tip and clay basal/edge surfaces were fitted with the classical DLVO (Derjaguin-Landau-Verwey-Overbeek) theory, which allows direct determination of electrical surface potential of talc and muscovite surfaces. The surface potential of muscovite basal planes was found to be significantly more negative than the basal plane of talc, both being pH insensitive. In contrast, the surface potential of edge surfaces was highly pH-dependent, exhibiting a point of zero charge (PZC) at pH 7.5 and 8.1 for edges of muscovite and talc, respectively. The observed differences in surface potential of basal planes and edge surfaces for both talc and muscovite are closely related to their crystal structure and ionization characteristics. The protonation reactivity and the contribution of each surface group to the surface charging behavior are modeled using their protonation constants.
为了从根本上理解粘土矿物的电动行为，有必要研究粘土表面的各向异性表面电荷特性。在这项研究中，选择两种 2:1 层天然矿物，滑石和白云母，分别作为镁质和铝质层状硅酸盐矿物的代表。这两种片状矿物的分子平滑基面都是通过沿基面劈开获得的，而合适的边缘面则是通过超微切片技术制备的。氮化硅原子力显微镜探针用于研究在各种 pH 值的水溶液中，探针与粘土基面/边缘表面之间的相互作用力。用经典的 DLVO（德贾金-朗道-范维尔-奥弗贝克）理论拟合探针与粘土基面/边缘表面之间测量的相互作用力曲线，可以直接确定滑石和白云母表面的电表面电位。白云母基面的表面电位明显比滑石的基面更负，两者都对 pH 不敏感。相比之下，边缘表面的表面电位对 pH 高度依赖，白云母和滑石的边缘分别在 pH 7.5 和 8.1 处表现出零电荷点（PZC）。滑石和白云母的基面和边缘表面的表面电位差异与其晶体结构和电离特性密切相关。使用质子化常数对质子化反应性和每个表面基团对表面荷电行为的贡献进行建模。
