Langmuir. 2018 Jun 26;34(25):7248-7263. doi: 10.1021/acs.langmuir.8b00797. Epub 2018 Jun 13.
nm-Range forces acting between calcite surfaces in water affect macroscopic properties of carbonate rocks and calcite-based granular materials and are significantly influenced by calcite surface recrystallization. We suggest that the repulsive mechanical effects related to nm-scale surface recrystallization of calcite in water could be partially responsible for the observed decrease of cohesion in calcitic rocks saturated with water. Using the surface forces apparatus, we simultaneously followed the calcite reactivity and measured the forces in water in two surface configurations: between two rough calcite surfaces (CC) and between rough calcite and a smooth mica surface (CM). We used nm-scale rough, polycrystalline calcite films prepared by atomic layer deposition. We measured only repulsive forces in CC in CaCO-saturated water, which was related to roughness and possibly to repulsive hydration effects. Adhesive or repulsive forces were measured in CM in CaCO-saturated water depending on calcite roughness, and the adhesion was likely enhanced by electrostatic effects. The pull-off adhesive force in CM became stronger with time, and this increase was correlated with a decrease of roughness at contacts, the parameter which could be estimated from the measured force-distance curves. That suggested a progressive increase of real contact areas between the surfaces, caused by gradual pressure-driven deformation of calcite surface asperities during repeated loading-unloading cycles. Reactivity of calcite was affected by mass transport across nm- to μm-thick gaps between the surfaces. Major roughening was observed only for the smoothest calcite films, where gaps between two opposing surfaces were nm-thick over μm-sized areas and led to force of crystallization that could overcome confining pressures of the order of MPa. Any substantial roughening of calcite caused a significant increase of the repulsive mechanical force contribution.
nm 级范围内的碳酸钙表面间的相互作用力会影响碳酸盐岩石和碳酸钙基粒状材料的宏观性质，并且会显著受到碳酸钙表面再结晶的影响。我们认为，nm 尺度范围内碳酸钙在水中的表面再结晶引起的机械排斥效应可能部分解释了在饱和水的方解石岩石中观察到的内聚力下降现象。我们使用表面力仪，同时跟踪碳酸钙的反应性并在两种表面构型下测量水中的力：两个粗糙碳酸钙表面（CC）之间和粗糙碳酸钙与光滑云母表面（CM）之间。我们使用原子层沉积制备的 nm 尺度粗糙多晶碳酸钙薄膜。我们仅在 CC 中测量到 CaCO₃ 饱和水中的排斥力，这与粗糙度有关，可能与排斥水合作用有关。在 CM 中，在 CaCO₃ 饱和水中测量到的力可能是粘附力或排斥力，这取决于碳酸钙的粗糙度，并且可能会增强静电效应。CM 中的拉脱粘附力随时间增强，这种增加与接触处粗糙度的降低相关，该参数可以从测量的力-距离曲线中估计。这表明，在重复加载-卸载循环过程中，碳酸钙表面微凸体在压力驱动下逐渐变形，导致表面之间的真实接触面积逐渐增加。碳酸钙的反应性受到表面之间的纳米到微米厚间隙中质量传递的影响。仅在最光滑的碳酸钙薄膜中观察到明显的粗化现象，其中两个相对表面之间的间隙在纳米范围内，覆盖了微米级的区域，导致结晶力足以克服 MPa 量级的围压。碳酸钙的任何实质性粗化都会显著增加排斥力。
