Direct evidence of heterogeneous mechanical relaxation in supercooled liquids
Direct evidence of heterogeneous mechanical relaxation in supercooled liquids
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DOI：
10.1103/physreve.84.061503
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发表时间：
2011-12-14
影响因子：
2.4
通讯作者：
Tanaka, Hajime
中科院分区：
文献类型：
--
作者：
Furukawa, Akira;Tanaka, Hajime
动态非均质性现在被认为是过冷液体的内在动力学特征。在这里，我们使用分子动力学模拟获得了玻璃形成液体的非局部复模量。我们发现剪切应力松弛在过冷状态下表现出明显的波数依赖性。这种相关性提供了直接证据，证明缓慢的机械松弛在空间中是不均匀发生的。其特征长度xi随温度的降低而增大，并变为介观结构。响应涉及粒子在xi上的重排，所需的时间与结构弛豫时间相当。我们的发现表明非均质结构弛豫在过冷液体的异常粘输运和粘弹性中具有重要意义。
Dynamic heterogeneity is now considered to be an intrinsic kinetic feature of a supercooled liquid. Here, we access the nonlocal complex modulus of a glass-forming liquid using molecular dynamics simulations. We find that the shear-stress relaxation exhibits a marked wave number dependence in a supercooled state. This dependence provides direct evidence that slow mechanical relaxation takes place heterogeneously in space. Its characteristic length xi increases with decreasing temperature and becomes mesoscopic. The response involves particle rearrangements over xi and takes a time comparable to the structural relaxation time tau(alpha). Our finding suggests that the heterogeneous structural relaxation is of fundamental importance in anomalous viscous transport and viscoelasticity in supercooled liquids.