Microscopic identification of the order parameter governing liquid-liquid transition in a molecular liquid
Microscopic identification of the order parameter governing liquid-liquid transition in a molecular liquid
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DOI：
10.1073/pnas.1501149112
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发表时间：
2015-05-12
影响因子：
11.1
通讯作者：
Tanaka, Hajime
中科院分区：
文献类型：
--
作者：
Murata, Ken-ichiro;Tanaka, Hajime
单组分物质中的液-液转变（LLT）是从一种液体到另一种液体的非常规相变。LLT最近引起了相当大的关注，因为它在我们理解液态中的重要性。为了从微观的角度访问LLT的序参数，在这里，我们遵循的有机分子液体，亚磷酸三苯酯（TPP）的LLT过程中的结构演变，通过时间分辨的小角和广角X射线散射测量。我们发现，在LLT期间，自发形成特征尺寸为几纳米的局部有利团簇，并且它们的数密度单调增加。这有力地表明，LLT的序参数是局部有利结构的数密度和非保守的性质。我们还表明，本地有利的结构是不同的晶体结构，这两种类型的有序相互竞争。因此，我们的研究不仅通过实验确定了控制LLT的结构序参量，而且还可能解决关于TPP中过渡性质的长期争论，即，无论转变是LLT还是仅仅是微晶形成。
A liquid-liquid transition (LLT) in a single-component substance is an unconventional phase transition from one liquid to another. LLT has recently attracted considerable attention because of its fundamental importance in our understanding of the liquid state. To access the order parameter governing LLT from a microscopic viewpoint, here we follow the structural evolution during the LLT of an organic molecular liquid, triphenyl phosphite (TPP), by time-resolved small-and wide-angle X-ray scattering measurements. We find that locally favored clusters, whose characteristic size is a few nanometers, are spontaneously formed and their number density monotonically increases during LLT. This strongly suggests that the order parameter of LLT is the number density of locally favored structures and of nonconserved nature. We also show that the locally favored structures are distinct from the crystal structure and these two types of orderings compete with each other. Thus, our study not only experimentally identifies the structural order parameter governing LLT, but also may settle a long-standing debate on the nature of the transition in TPP, i.e., whether the transition is LLT or merely microcrystal formation.