The devil is in the details: pentagonal bipyramids and dynamic arrest
The devil is in the details: pentagonal bipyramids and dynamic arrest
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DOI：
10.1088/1742-5468/ab5369
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发表时间：
2020-01-01
影响因子：
2.4
通讯作者：
Royall, C. Patrick
中科院分区：
文献类型：
--
作者：
Hallett, James E.;Turci, Francesco;Royall, C. Patrick
胶体悬浮液长期以来一直被研究作为原子和分子系统的模型，由于荧光标记和单独跟踪每个颗粒的能力，产生颗粒分辨的结构信息。这允许探测各种局部有序参数，这些参数对于可比较的分子系统来说是不可接近的。对于相变，如结晶，适当的顺序参数，强调6重对称性是一个自然的选择，但对于玻璃化的顺序参数的选择是不太明确的。以前的工作已经强调了二十面体局部结构的重要性，玻璃化转变的方法。然而，计数二十面体或相关基序不是连续的序参数，例如键取向序参数Q（6）和W-6。在这项工作中，我们调查的适用性，使用五角双锥的成员资格，可以组装成更大的，五重对称结构的结构，作为一个更精细的序参量调查的玻璃化转变。我们探索了各种结构和动态特性，并表明这种新方法产生了许多与简单二十面体成员相同的发现，但我们也发现，大的瞬时位移往往与五角双锥成员的显着变化相关，并且与缺陷二十面体的人口不同，五角双锥成员和主轴数对于任何测量的体积分数都不饱和，而且还在继续增加。
Colloidal suspensions have long been studied as a model for atomic and molecular systems, due to the ability to fluorescently label and individually track each particle, yielding particle-resolved structural information. This allows various local order parameters to be probed that are otherwise inaccessible for a comparable molecular system. For phase transitions such as crystallisation, appropriate order parameters which emphasise 6-fold symmetry are a natural choice, but for vitrification the choice of order parameter is less clear cut. Previous work has highlighted the importance of icosahedral local structure as the glass transition is approached. However, counting icosahedra or related motifs is not a continuous order parameter in the same way as, for example, the bond-orientational order parameters Q(6) and W-6. In this work we investigate the suitability of using pentagonal bipyramid membership, a structure which can be assembled into larger, five-fold symmetric structures, as a finer order parameter to investigate the glass transition. We explore various structural and dynamic properties and show that this new approach produces many of the same findings as simple icosahedral membership, but we also find that large instantaneous displacements are often correlated with significant changes in pentagonal bipyramid membership, and unlike the population of defective icosahedra, the pentagonal bypyramid membership and spindle number do not saturate for any measured volume fraction, but continue to increase.