Kawasaki Takeshi, Kim Kang
Department of Physics, Nagoya University, Nagoya 464-8602, Japan.
Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University, Osaka 560-8531, Japan.
Sci Adv. 2017 Aug 18;3(8):e1700399. doi: 10.1126/sciadv.1700399. eCollection 2017 Aug.
The violation of the Stokes-Einstein (SE) relation ~ (η/) between the shear viscosity η and the translational diffusion constant at temperature is of great importance for characterizing anomalous dynamics of supercooled water. Determining which time scales play key roles in the SE violation remains elusive without the measurement of η. We provide comprehensive simulation results of the dynamic properties involving η and in the TIP4P/2005 supercooled water. This enabled the thorough identification of the appropriate time scales for the SE relation η/. In particular, it is demonstrated that the temperature dependence of various time scales associated with structural relaxation, hydrogen bond breakage, stress relaxation, and dynamic heterogeneities can be definitely classified into only two classes. That is, we propose the generalized SE relations that exhibit "violation" or "preservation." The classification depends on the examined time scales that are coupled or decoupled with the diffusion. On the basis of the classification, we explain the physical origins of the violation in terms of the increase in the plateau modulus and the nonexponentiality of stress relaxation. This implies that the mechanism of SE violation is attributed to the attained solidity upon supercooling, which is in accord with the growth of non-Gaussianity and spatially heterogeneous dynamics.
在温度(T)下，剪切粘度(\eta)与平动扩散常数(D)之间违反斯托克斯 - 爱因斯坦（SE）关系(\sim(\eta/D))对于表征过冷水的反常动力学非常重要。在没有测量(\eta)的情况下，确定哪些时间尺度在SE关系违反中起关键作用仍然难以捉摸。我们提供了TIP4P / 2005过冷水中涉及(\eta)和(D)的动态特性的综合模拟结果。这使得能够彻底确定SE关系(\eta/D)的适当时间尺度。特别是，证明了与结构弛豫、氢键断裂、应力弛豫和动态非均匀性相关的各种时间尺度的温度依赖性可以明确地分为仅两类。也就是说，我们提出了表现出“违反”或“保持”的广义SE关系。这种分类取决于与扩散耦合或解耦的检查时间尺度。基于这种分类，我们根据高原模量的增加和应力弛豫的非指数性来解释违反的物理起源。这意味着SE违反的机制归因于过冷时达到的固态，这与非高斯性和空间非均匀动力学的增长一致。
