Hydration breaking and chemical ordering in a levitated NaCl solution droplet beyond the metastable zone width limit: evidence for the early stage of two-step nucleation.
Hydration breaking and chemical ordering in a levitated NaCl solution droplet beyond the metastable zone width limit: evidence for the early stage of two-step nucleation.
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在悬浮的NaCl溶液液滴中，水合破裂和化学排序超出了亚稳态宽度极限：两步成核的早期阶段的证据。
DOI：
10.1039/d0sc04817h
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发表时间：
2020-12-09
期刊：
影响因子：
8.4
通讯作者：
Lee GW
中科院分区：
文献类型：
--
作者：
Hwang H;Cho YC;Lee S;Lee YH;Kim S;Kim Y;Jo W;Duchstein P;Zahn D;Lee GW
二十多年来，已经预测过饱和水溶液的NaCl成核通过两步成核（TSN）机制发生，即，两个连续的事件，形成局部致密的液体区域，然后是结构有序化。然而，在TSN的非常早期阶段的致密液体区域的形成从未被实验观察到。通过使用一个国家的最先进的技术，静电悬浮（ESL）和原位同步X射线和拉曼散射的组合，我们发现实验证据表明，在NaCl本体溶液中形成致密的液体区域在一个前所未有的高水平的过饱和度（S = 2.31）。随着过饱和度的增加，离子团簇的演化导致化学有序化，但不导致拓扑有序化，这是在TSN早期形成离子团簇密集无序区的前兆。此外，由于离子簇在高度过饱和的条件下进行演变，我们观察到的水的水合结构的破坏，表明致密的液体区域的稳定性极限，从而导致成核。高过饱和NaCl溶液中溶质团簇的演化和水化的破坏将为许多其他水溶液的TSN的详细机制提供新的见解。这项工作提供了证据的两步成核在高度过饱和体氯化钠溶液中，使用静电悬浮结合拉曼/X射线散射。
For over two decades, NaCl nucleation from a supersaturated aqueous solution has been predicted to occur via a two-step nucleation (TSN) mechanism, i.e., two sequential events, the formation of locally dense liquid regions followed by structural ordering. However, the formation of dense liquid regions in the very early stage of TSN has never been experimentally observed. By using a state-of-the-art technique, a combination of electrostatic levitation (ESL) and in situ synchrotron X-ray and Raman scatterings, we find experimental evidence that indicates the formation of dense liquid regions in NaCl bulk solution at an unprecedentedly high level of supersaturation (S = 2.31). As supersaturation increases, evolution of ion clusters leads to chemical ordering, but no topological ordering, which is a precursor for forming the dense disordered regions of ion clusters at the early stage of TSN. Moreover, as the ion clusters proceed to evolve under highly supersaturated conditions, we observe the breakage of the water hydration structure indicating the stability limit of the dense liquid regions, and thus leading to nucleation. The evolution of solute clusters and breakage of hydration in highly supersaturated NaCl bulk solution will provide new insights into the detailed mechanism of TSN for many other aqueous solutions. This work provides evidence for two-step nucleation in highly supersaturated bulk NaCl solution, using electrostatic levitation combined with Raman/X-ray scatterings.
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