The interface between aqueous solutions and the facets of kaolinite plays an important role in a wide range of technological applications including tribology, paper production, oil recovery, waste water treatment and medical devices. This is made possible by kaolinite's layered structure, with its two basal surfaces -aluminol and siloxane-exhibiting different properties and reactivity. Using a combination of high-resolution atomic force microscopy (AFM) and atomistic molecular dynamics (MD) simulations, we probe the hydration structure over both facets, in water and in the presence of added NaCl. The AFM images reflect the facets' first hydration layer, as confirmed from simulations. Complementary AFM spectroscopy measurements show an excellent agreement between the conservative component and MD's water density profiles, with discrete hydration layers on both facets and little sensitivity to added ions. The dissipative component of the measured tip-sample interactions is more sensitive to the presence of ions, with MD suggesting a link with the local water dynamics and transient instabilities between stable hydration layers. These effects are facet-dependant and more pronounced on the aluminol facet where the first water layer is better defined. Increasing the salt concentration allows hydrated ions to form more stable layers, with hints of organised ionic domains. The results provide unique insights into both the equilibrium molecular structure and dynamics of the kaolinite facets, potentially informing applications involving interfacial processes.

中文翻译：

---

离子存在下高岭石基面纳米级水化景观的局部探测


水溶液和高岭石晶面之间的界面在摩擦学、造纸、石油回收、废水处理和医疗设备等广泛的技术应用中发挥着重要作用。这是通过高岭石的层状结构实现的，其两个基面（铝醇和硅氧烷）表现出不同的性能和反应性。通过结合高分辨率原子力显微镜 (AFM) 和原子分子动力学 (MD) 模拟，我们探测了在水中和添加 NaCl 的情况下两个方面的水合结构。正如模拟所证实的那样，AFM 图像反映了刻面的第一水化层。互补的 AFM 光谱测量显示保守成分和 MD 的水密度分布之间具有极好的一致性，两个面上都有离散的水化层，并且对添加的离子几乎不敏感。测得的尖端-样品相互作用的耗散分量对离子的存在更敏感，MD表明与局部水动力学和稳定水化层之间的瞬态不稳定性有关。这些影响取决于刻面，并且在铝醇刻面上更为明显，其中第一水层被更好地限定。增加盐浓度可以使水合离子形成更稳定的层，并带有组织化离子域的迹象。这些结果为高岭石晶面的平衡分子结构和动力学提供了独特的见解，可能为涉及界面过程的应用提供信息。