Jump-precursor state emerges below the crossover temperature in supercooled o -terphenyl
Jump-precursor state emerges below the crossover temperature in supercooled o -terphenyl
复制标题
过冷邻三联苯中跃迁前体态出现在交叉温度以下
DOI：
10.1103/physreve.103.l050601
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发表时间：
2021
影响因子：
2.4
通讯作者：
Berg, Mark A.
中科院分区：
文献类型：
--
作者：
Kaur, Harveen;Berg, Mark A.
在过冷液体中，交叉温度将扩散动力学的高温区域与活化动力学的低温区域分开。用先进的统计方法分析全原子柔性三联苯的分子动力学模拟[Eastwood，J.Phys.Chem.B 117，12898（2013）10.1021/jp402102 w]，以揭示与该交叉相关的分子特征。模拟扩展到14 μ s（272.5 K）的α弛豫时间，比290 K慢两个数量级。在这一点上，一个明显的状态出现了，紧接着就是一个定向跳跃.与初始的紧密笼状态相比，这种跳跃前体态具有更松散的笼状，具有0.054 - 0.0125 × 4 π sr的立体角偏移。在（290 K），速率不均匀性已经是拉伸弛豫的主要原因。速率分布内的交换比α弛豫快，但在模拟的最低温度（272.5 K）时变得与α弛豫相等。结果倾向于最近在玻璃化转变（243 K）附近的实验观察[Kaur，Phys. Rev. E 98，040603（R）（2018）10.1103/PhysRevE.98.040603]，其中交换比α弛豫慢得多。总的来说，动态交叉包括多种现象：异质性的发展，增加跳跃的大小，新兴的跳跃前兆状态，和延长交换时间。这种交叉既不明显，也不是高温和低温状态的简单叠加;它是一个包含独特和复杂现象的广阔区域。
In a supercooled liquid, the crossover temperatureseparates a high-temperature region of diffusive dynamics from a low-temperature region of activated dynamics. A molecular-dynamics simulation of all-atom, flexible-terphenyl [Eastwood , J. Phys. Chem. B 117, 12898 (2013)10.1021/jp402102w] is analyzed with advanced statistical methods to reveal the molecular features associated with this crossover. The simulations extend to an α-relaxation time of 14 μs (272.5 K), two orders of magnitude slower than at(290 K). Atand below, a distinct state emerges that immediately precedes an orientational jump. Compared to the initial, tightly caged state, this jump-precursor state has a looser cage, with solid-angular excursions of 0.054–0.0125 × 4π sr. At(290 K), rate heterogeneity is already the dominant cause of stretched relaxation. Exchange within the distribution of rates is faster than α relaxation at, but becomes equal to it at the lowest temperature simulated (272.5 K). The results trend toward a recent experimental observation near the glass transition (243 K) [Kaur , Phys. Rev. E 98, 040603(R) (2018)10.1103/PhysRevE.98.040603], which saw exchange substantially slower than α relaxation. Overall, the dynamic crossover comprises multiple phenomena: the development of heterogeneity, an increasing jump size, an emerging jump-precursor state, and a lengthening exchange time. The crossover is neither sharp, nor a simple superposition of the high- and low-temperature regimes; it is a broad region that contains unique and complex phenomena.