How does a transient amorphous precursor template crystallization.
How does a transient amorphous precursor template crystallization.
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DOI：
10.1021/ja073598k
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发表时间：
2007-10
影响因子：
15
通讯作者：
T. Zhang;Xiang‐Yang Liu
中科院分区：
文献类型：
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作者：
T. Zhang;Xiang‐Yang Liu
亚稳相的结晶，如多晶性，在化学制造、生物矿化和蛋白质结晶中起着重要作用。然而，从亚稳相生成最终稳定晶相的动力学到目前为止还不清楚。本研究在胶体模型体系中定量地研究了非晶态前驱体的结晶过程，即所谓的多步结晶(MSC)。在MSC中，无定形致密液滴首先从母相形核。随后，微小的致密液滴的涨落可以同时产生几个不稳定的亚晶核，这与以前的理论预测不同。这些晶核必须达到临界大小N*(Crys)才能变得稳定。然而，与亚晶核不同的是，稳定的成熟晶核不是由波动产生的，而是由亚晶核聚合而成的，这是意想不到的。为了容纳大于临界尺寸N*(Crys)的成熟晶核，致密液滴必须首先获得临界尺寸N*。这意味着只有一小部分无定形致密液滴可以作为晶体成核的先驱。因此，晶相的总体成核速率在很大程度上取决于晶体在致密液滴中的成核速率，远低于先前的理论预期。此外，令人惊讶的是，MSC将促进无缺陷晶体的生产。本研究所获得的知识也将极大地促进我们对多态相关过程的理解。
Crystallization through metastable phases, such as polymorphism, plays an important role in chemical manufacture, biomineralization, and protein crystallization. However, the kinetics creating the final stable crystalline phase from metastable phases has so far remained unclear. In this study, crystallization via an amorphous precursor, the so-called multistep crystallization (MSC), is studied quantitatively in a colloidal model system. In MSC, amorphous dense droplets are first nucleated from the mother phase. Subsequently, a few unstable subcrystalline nuclei can be created simultaneously by fluctuation from the tiny dense droplets, which is different from previous theoretical predictions. It is necessary for these crystalline nuclei to reach a critical size N*(crys) to become stable. However, in contrast to subcrystalline nuclei, a stable mature crystalline nucleus is not created by fluctuation but by coalescence of subcrystalline nuclei, which is unexpected. To accommodate a mature crystalline nucleus larger than the critical size N*(crys), the dense droplets have to first acquire a critical size N*. This implies that only a fraction of amorphous dense droplets can serve as a precursor of crystal nucleation. As an outcome, the overall nucleation rate of the crystalline phase is, to a large extent, determined by the nucleation rate of crystals in the dense droplets, which is much lower than the previous theoretical expectation. Furthermore, it is surprising to see that MSC will promote the production of defect-free crystals. The knowledge acquired in this study will also significantly advance our understandings in polymorphism related processes.