Gao Yitian, Wu Jian, Feng Yixuan, Han Jiale, Fang Hongwei
State Key Laboratory of Hydro-science and Engineering, Department of Hydraulic Engineering, Tsinghua University, Beijing 100084, China.
Department of Physics, Tsinghua University, Beijing 100084, China.
J Chem Phys. 2024 Mar 14;160(10). doi: 10.1063/5.0187906.
In this study, we use molecular dynamics simulations of liquid water to investigate how shear thinning affects the viscosity of liquid water by structural changes of the hydrogen bond network. The effect of shear on viscosity can be divided into two parts: shear-induced destruction of the hydrogen bond network and the influence of the water structure on shear viscosity. First, strong shear destroys tetrahedral structures and thus reduces the connectivity of the hydrogen bond network. It is mainly because shear deformation, characterized by compression and expansion axes, respectively, triggers the destruction and formation of hydrogen bonds, resulting in anisotropic effects on water structures. At the same time, shear destroys large clusters and enhances the formation of small ones, resulting in a decrease in average cluster sizes. Second, the change of viscosity obeys a power law relationship with the change of hydrogen bond structures, highlighting a one-to-one correspondence between structure and property. Meanwhile, in order to explain why the structure affects viscosity, we define hydrogen-bond viscosity and find that the cooperative motion of the water structures can promote momentum transfer in the form of aggregations. Hydrogen-bond viscosity accounts for 5%-50% of the total viscosity. Our results elucidate that water structures are the important structural units to explain the change of water properties.
在本研究中，我们利用液态水的分子动力学模拟来研究剪切变稀如何通过氢键网络的结构变化影响液态水的粘度。剪切对粘度的影响可分为两部分：剪切诱导的氢键网络破坏以及水结构对剪切粘度的影响。首先，强剪切破坏四面体结构，从而降低氢键网络的连通性。这主要是因为以压缩轴和膨胀轴为特征的剪切变形分别引发氢键的破坏和形成，导致对水结构产生各向异性效应。同时，剪切破坏大的团簇并增强小团簇的形成，导致平均团簇尺寸减小。其次，粘度的变化与氢键结构的变化服从幂律关系，突出了结构与性质之间的一一对应关系。同时，为了解释结构为何影响粘度，我们定义了氢键粘度，并发现水结构的协同运动会以聚集的形式促进动量传递。氢键粘度占总粘度的5% - 50%。我们的结果表明，水结构是解释水性质变化的重要结构单元。
