Interfaces can actively control the nucleation kinetics, orientations, and polymorphs of calcium carbonate (CaCO₃). Prior studies have revealed that CaCO₃ formation can be affected by the interplay between chemical functional moieties on solid–liquid or air–liquid interfaces as well as CaCO₃’s precursors and facets. Yet little is known about the roles of a liquid–liquid interface, specifically an oil–liquid interface, in directing CaCO₃ mineralization which are common in natural and engineered systems. Here, by using in situ X-ray scattering techniques to locate a meniscus formed between water and a representative oil, isooctane, we successfully monitored CaCO₃ formation at the pliable isooctane–water interface and systematically investigated the pivotal roles of the interface in the formation of CaCO₃ (i.e., particle size, its spatial distribution with respect to the interface, and its mineral phase). Different from bulk solution, ∼5 nm CaCO₃ nanoparticles form at the isooctane–water interface. They stably exist for a long time (36 h), which can result from interface-stabilized dehydrated prenucleation clusters of CaCO₃. There is a clear tendency for enhanced amounts and faster crystallization of CaCO₃ at locations closer to isooctane, which is attributed to a higher pH and an easier dehydration environment created by the interface and oil. Our study provides insights into CaCO₃ nucleation at an oil–water interface, which can deepen our understanding of pliable interfaces interacting with CaCO₃ and benefit mineral scaling control during energy-related subsurface operation.

中文翻译：

---

原位监测油-水界面处纳米级 CaCO3 的成核和生长


界面可以主动控制碳酸钙 （CaCO₃） 的成核动力学、取向和多晶型物。先前的研究表明，CaCO₃ 的形成会受到固-液或气-液界面上化学功能部分以及 CaCO₃ 的前体和刻面之间相互作用的影响。然而，人们对液-液界面，特别是油-液界面，在引导 CaCO₃ 矿化中的作用知之甚少，这在自然和工程系统中很常见。在这里，通过使用原位 X 射线散射技术定位在水和代表性油异辛烷之间形成的弯月面，我们成功监测了 CaCO₃ 在柔韧的异辛烷-水界面处的形成，并系统地研究了界面在 CaCO₃ 形成中的关键作用（即颗粒大小、其相对于界面的空间分布、 及其矿物相）。与本体溶液不同，∼5 nm CaCO₃ 纳米颗粒在异辛烷-水界面形成。它们稳定存在很长时间 （36 h），这可能是由 CaCO₃ 的界面稳定脱水前成核簇引起的。在更接近异辛烷的位置，CaCO₃ 的结晶量增加和结晶速度明显增加，这归因于更高的 pH 值以及界面和油产生的更容易脱水的环境。我们的研究提供了对油-水界面处 CaCO₃ 成核的见解，这可以加深我们对与 CaCO₃ 相互作用的柔韧界面的理解，并有利于在与能源相关的地下作业期间控制矿物结垢。