Department of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University , Aramakiaza-Aoba 6-3, Aoba-ku, Sendai 980-8578, Japan.
J Am Chem Soc. 2014 Feb 5;136(5):1762-5. doi: 10.1021/ja412111f. Epub 2014 Jan 27.
The formation of crystals from solution requires the initial self-assembly of units of matter into stable periodic structures reaching a critical size. The early stages of this process , called nucleation, are very difficult to visualize. Here we describe a novel method that allows real time observation of the dynamics of nucleation and dissolution of sodium chlorate clusters in an ionic liquid solution using in situ transmission electron microscopy. Using ionic liquids as solvent circumvents the problem of evaporation and charging, while the nucleation frequency was reduced by using saturated solutions. We observe simultaneous formation and dissolution of prenucleation clusters, suggesting that high-density fluctuations leading to solid cluster formation exist even under equilibrium conditions. In situ electron diffraction patterns reveal the simultaneous formation of crystalline nuclei of two polymorphic structures, the stable cubic phase and the metastable monoclinic phase, during the earliest stages of nucleation. These results demonstrate that molecules in solution can form clusters of different polymorphic phases independently of their respective solubility.
从溶液中形成晶体需要物质单元最初自组装成稳定的周期性结构，达到临界尺寸。这个过程的早期阶段，称为成核，非常难以可视化。在这里，我们描述了一种新的方法，允许使用原位透射电子显微镜实时观察氯酸钠簇在离子液体溶液中的成核和溶解动力学。使用离子液体作为溶剂可以避免蒸发和充电的问题，而使用饱和溶液则降低了成核频率。我们观察到预成核簇的同时形成和溶解，表明即使在平衡条件下，也存在导致固体簇形成的高密度涨落。原位电子衍射图案揭示了在成核的最早阶段，两种多晶型结构（稳定的立方相和亚稳的单斜相）的晶核同时形成。这些结果表明，溶液中的分子可以形成不同多晶型相的簇，而与其各自的溶解度无关。
