Graduate School of Engineering, Nagoya University, Furo-cho B2-3 (611), Chikusa, Nagoya, Aichi 464-8603, Japan.
J Chem Phys. 2018 Jun 21;148(23):234507. doi: 10.1063/1.5026536.
The cross correlation between the two-body density and shear stress of Lennerd-Jones liquids is evaluated by means of equilibrium molecular dynamics (MD) simulation in order to clarify the microscopic structure that determines the shear viscosity. The slowest viscoelastic relaxation is coupled to the shift of the main peak of the static structure factor as is predicted by mode-coupling theory (MCT). The decay of the cross-correlation function in the reciprocal space is explained by the square of the intermediate scattering function, which is also in harmony with MCT. The distortion of the microscopic structure under simple shear is calculated by means of non-equilibrium MD simulation. The linear response relation also holds on the two-body density within the Newtonian regime of shear viscosity, while the structural distortion diminishes in the shear-thinning regime. The transition between the Newtonian and the shear-thinning regimes occurs at the shear rate where the magnitude of the structural distortion becomes as large as that of the equilibrium structure. The breakdown of the Cox-Merz rule is ascribed to the narrow width of the main peak of the static structure factor.
采用平衡分子动力学（MD）模拟方法评估 Lennard-Jones 液体的双体密度与剪切应力的交叉关联，以阐明决定剪切黏度的微观结构。最慢的黏弹弛豫与静态结构因子主峰值的移动相关联，这正如模式耦合理论（MCT）所预测的那样。倒空间中交叉相关函数的衰减可以用中间散射函数的平方来解释，这也与 MCT 相符。通过非平衡 MD 模拟计算简单剪切下的微观结构变形。在牛顿剪切黏度区域内，线性响应关系也适用于双体密度，而在剪切变稀区域内，结构变形会减小。在牛顿和剪切变稀区域之间的转变发生在结构变形的大小与平衡结构相当时的剪切速率处。Cox-Merz 规则的失效归因于静态结构因子主峰值的较窄宽度。
