Influence of Softness on the Stability of Binary Colloidal Crystals
Influence of Softness on the Stability of Binary Colloidal Crystals
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DOI：
10.1021/acsnano.9b04274
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发表时间：
2019-12-01
期刊：
影响因子：
17.1
通讯作者：
Glotzer, Sharon C.
中科院分区：
文献类型：
--
作者：
LaCour, R. Allen;Adorf, Carl Simon;Glotzer, Sharon C.
两种类型的纳米粒子的混合物可以自组装成各种各样的二元胶体晶体（也称为二元纳米粒子超晶格），这是有趣的结构多样性和潜在的应用。虽然所谓的堆积模型通常将颗粒视为“硬的”，只排除体积相互作用，似乎可以解释许多报道的致密结晶相，但这些模型往往无法预测正确的结构。在这里，我们研究软排斥粒子间相互作用的二元胶体晶体，包括两种尺寸的球形颗粒的作用，这种“柔软性”可能会出现由于配体壳或屏蔽静电。我们确定的基态相图的粒子与添加剂的逆幂律势相互作用的二元系统使用盆跳跃算法计算的一个非常大的池的候选结构的焓。我们发现，一个令人惊讶的少量的柔软度可以不稳定的密集包装有利于不太密集的包装结构，这提供了进一步的证据，包装以外的考虑是必要的描述许多观察到的二元胶体晶体的阶段。重要的是，我们发现，几个相稳定的软，其特征在于相对较少的颗粒间接触和局部二十面体秩序的趋势，更有可能被观察到的实验比那些预测的包装模型。我们还报告了一种以前未知的致密AB（4）相，并进行自由能计算以研究几种晶体的稳定性如何随温度变化。我们的研究结果进一步了解为什么特定的二元胶体晶体的形式，并将是有用的，作为一个参考实验工作与软排斥胶体。
Mixtures of two types of nanoparticles can self-assemble into a wide variety of binary colloidal crystals (also called binary nanoparticle superlattices), which are interesting for their structural diversity and potential applications. Although so-called packing models-which usually treat the particles as "hard" with only excluded volume interactions-seem to explain many reported dense crystalline phases, these models often fail to predict the right structure. Here, we examine the role of soft repulsive interparticle interactions on binary colloidal crystals comprising two sizes of spherical particles; such "softness" can arise due to ligand shells or screened electrostatics. We determine the ground state phase diagram of binary systems of particles interacting with an additive inverse power law potential using a basin hopping algorithm to calculate the enthalpy of an extremely large pool of candidate structures. We find that a surprisingly small amount of softness can destabilize dense packings in favor of less densely packed structures, which provides further evidence that considerations beyond packing are necessary for describing many of the observed phases of binary colloidal crystals. Importantly, we find that several of the phases stabilized by softness, which are characterized by relatively few interparticle contacts and a tendency for local icosahedral order, are more likely to be observed experimentally than those predicted by packing models. We also report a previously unknown dense AB(4) phase and conduct free energy calculations to examine how the stability of several crystals will vary with temperature. Our results further our understanding of why particular binary colloidal crystals form and will be useful as a reference for experimentalists working with softly repulsive colloids.