Characterization of Preferred Crystal Nucleation Sites on Mica Surfaces
Characterization of Preferred Crystal Nucleation Sites on Mica Surfaces
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DOI：
10.1021/cg301715n
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发表时间：
2013-05-01
影响因子：
3.8
通讯作者：
Christenson, Hugo K.
中科院分区：
文献类型：
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作者：
Campbell, James M.;Meldrum, Fiona C.;Christenson, Hugo K.
异质成核速率不仅可以通过控制表面的化学成分，而且还可以通过控制其表面的形貌来大大提高。在我们之前的工作中，我们证明了划痕云母表面显著增强了水蒸气中的晶体成核，现在我们使用一种新的实验方法来更好地了解地形对晶体成核的影响。将四溴化碳、樟脑、降冰片和六氯乙烷从水蒸气中沉积到含有各种表面缺陷的云母片上，并用光学显微镜研究了它们的成核。在随后的晶体蒸发之后，用扫描电子显微镜检查这些晶体的成核位置，能够确定每种材料的首选成核位置的性质，并且所有四种化合物似乎都表现出对以层状云母结构分层为特征的位置的强烈偏好。事实上，四种化合物在相同的云母底物上的比较表明，它们都有利于相同的成核位置。这些观察结果归因于分层线处存在尖锐的楔形几何结构，这可以从热力学上降低直接从蒸汽成核的自由能垒；或者，结果也与通过液体毛细冷凝的两步成核机制一致。
Rates of heterogeneous nucleation can be greatly increased not only through control of the chemistry of a surface, but also of its topography. Following previous work in which we showed that scratching a mica surface significantly enhances crystal nucleation from vapor, we here use a new experimental approach to understand better the effect of topography on crystal nucleation. The compounds carbon tetrabromide, camphor, norbornane, and hexachloroethane were deposited from vapor onto mica sheets containing various surface defects, and their nucleation was studied using optical microscopy. Following subsequent evaporation of the crystals, examination of the sites where these had nucleated with a scanning electron microscope enabled the nature of each material's preferred nucleation sites to be determined, and all four compounds appeared to exhibit a strong preference for sites characterized by delamination of the layered, mica structure. Indeed, comparison of the, four compounds on the same mica substrates showed that they all favored the same nucleation sites. These observations are attributed to the presence of an acute wedge geometry at the delamination lines, which can provide a thermodynamic reduction in the free energy barrier to nucleation directly from vapor; alternatively, the results are also consistent with a two-step nucleation mechanism via a liquid capillary condensate.