聚结胶体纳米晶的液相生长
Liquid-like growth of colloidal nanocrystals of coalescence
摘要：
我们对晶体生长的理解主要是由经典的描述，根据该描述，单个原子或分子在过饱和的驱动下添加到晶体小平面。因此，硬物质的生长仍然被认为基本上无法与软物质（如聚合物或液体）的生长相比。通过实验和建模的结合，我们在这里展示了胺封端的PbS胶体纳米粒子如何在没有过饱和的情况下通过聚结生长，就像乳液中的液滴一样。具体来说，我们（i）确定晶体-晶体聚结的速率非常高（10^-2 ~ 10^1 M^-1*s^-1），与双分子反应的结果相当，（从而为开发反应物是胶体而不是分子的化学形式提供了新的途径），（ii）阐明速率限制步骤的晶体-晶体聚结导致我们提出的设计规则来控制它，和（iii）演示一个简单的，两个参数的模型，定量预测这个过程及其对配体的依赖。最后，我们使用布朗动力学模拟来说明拥挤效应和相对较大的颗粒尺寸与其平均自由程相比如何解释这些显着较大的聚结速率，同时，先前报道的定向附着过程的活化能值低得令人困惑。
英文摘要：
Our understanding of the growth of crystals is dominated by the classical description according to which individual atoms or molecules, driven by supersaturation, add to crystal facets. As a result, the growth of hard matter is still mostly considered to be fundamentally incomparable to the growth of soft matter, like polymers or liquids. By a combination of experiment and modeling we here show how amine-capped PbS colloidal nanoparticles grow in the absence of supersaturation by coalescence, like droplets in an emulsion. Specifically, we (i) determine that the rates of crystal-crystal coalescence are remarkably high (10^-2 to 10^1 M^-1*s^-1) in spite of the steric stabilization of the particles, and are comparable to those of bimolecular reactions, (thereby providing a new avenue for the development of a form of chemistry where the reactants are colloids rather than molecules), (ii) elucidate the rate limiting steps of crystal-crystal coalescence leading us to propose design rules to control it, and (iii) demonstrate a simple, two-parameter model that predicts quantitatively this process and its dependence on the ligands. Lastly, we use Brownian dynamics simulations to show how crowding effects and the relatively large size of the particles compared to their mean free path explain these remarkably large rates of coalescence and, at the same time, the puzzlingly low values of activation energy previously reported for oriented attachment processes.
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