The emergence of cooperativity accompanying vitrification: insights from density fluctuation dynamics
The emergence of cooperativity accompanying vitrification: insights from density fluctuation dynamics
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伴随玻璃化的协同性的出现：密度波动动力学的见解
DOI：
10.1088/1742-5468/ab2ad0
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
A. Furukawa
中科院分区：
文献类型：
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作者：
A. Furukawa
基于脆性玻璃形成液体的密度涨落动力学，讨论了玻璃化过程中协同效应的产生和发展。(i)密度涨落的弛豫是通过粒子（密度）交换过程进行的，并且是扩散的;也就是说，允许的动力学路径受到局部守恒定律的强烈限制。(ii)在正常的液体状态下，这种交换过程是不太合作的，并且密度波动的扩散系数Dc被给出为，其中是颗粒尺寸，并且是结构弛豫时间。另一方面，在过冷状态下，随着过冷度的增加，对动力学路径的限制更加严重，这使得交换过程更加合作，导致具有合作长度尺度。(iii)分子动力学模拟结果表明，标记粒子的自扩散系数Ds与Dc几乎一致，表明集体密度扩散与粒子扩散具有相同的机制：正常态下Ds决定Dc，过冷态下Ds决定Dc.这立即导致了这样的想法，即斯托克斯-爱因斯坦关系的破裂不是单粒子动力学中的异常，而是反映了在长度尺度上密度扩散中协同性的增加。
We discuss the emergence and growth of the cooperativity accompanying vitrification based on the density fluctuation dynamics for fragile glass-forming liquids. (i) The relaxation of density fluctuations proceeds by the particle (density) exchange process, and is diffusive; that is, the allowable kinetic paths are strongly restricted by the local conservation law. (ii) In normal liquid states, this exchange process is less cooperative, and the diffusion coefficient of density fluctuations Dc is given as , where is the particle size and is the structural relaxation time. On the other hand, in supercooled states the restriction on the kinetic path is more severe with increasing the degree of supercooling, which makes the exchange process more cooperative, resulting in with being the cooperative length scale. (iii) The molecular dynamics simulation results show that the self-diffusion coefficient of the tagged particle, Ds, almost coincides with Dc, suggesting that the collective density diffusion and the particle diffusion closely share the same mechanism: in normal states Ds determines Dc, but vice versa in supercooled states. This immediately leads to the idea that the breakdown of the Stokes–Einstein relation is not the anomaly in the single-particle dynamics but reflects the increase in the cooperativity in the density diffusion at the length scale of .