摘要
用 nonequilibrium 分子的动力学模拟，我们学习 Lennard-Jones 潜力管理的单原子的液体的非牛顿的 rheological 行为。两稳定的 Couette 并且摆动砍流动被调查。砍变瘦并且正常压力效果在稳定的 Couette 流动模拟被观察。光线的分发功能被计算在不同砍展出分子的显微镜的结构的变化由于的率砍。我们观察那为一更大砍评价当吸引力更弱时，在分子之间的排斥是更强大的，并且上述现象能被势能的分析也证实。由适用一摆动砍到系统，几调查结果值得这里提及：首先， shear 之间的阶段差别强调率与频率增加并且砍。第二，复杂粘性的真实部分首先增加然后当想象的部分趋于 monotonically 增加时，减少，它与增加的频率导致想象的部分的比例的增加到真实部分。第三，有弹性的模量到的比率粘滞模量也与频率增加。这些现象都为 Lennard-Jones 液体在高摆动频率在粘性上显示粘弹性的外观和弹性的支配。
Using nonequilibrium molecular dynamics simulations, we study the non-Newtonian rhe-ological behaviors of a monoatomic fluid governed by the Lennard-Jones potential. Both steady Couette and oscillatory shear flows are investigated. Shear thinning and normal stress effects are observed in the steady Couette flow simulations. The radial distribution function is calculated at different shear rates to exhibit the change of the microscopic struc- ture of molecules due to shear. We observe that for a larger shear rate the repulsion between molecules is more powerful while the attraction is weaker, and the above phenomena can also be confirmed by the analyses of the potential energy. By applying an oscillatory shear to the system, several findings are worth mentioning here： First, the phase difference between the shear stress and shear rate increases with the frequency. Second, the real part of complex viscosity first increases and then decreases while the imaginary part tends to increase mono- tonically, which results in the increase of the proportion of the imaginary part to the real part with the increasing frequency. Third, the ratio of the elastic modulus to the viscous modulus also increases with the frequency. These phenomena all indicate the appearance of viscoelasticity and the domination of elasticity over viscosity at high oscillation frequency for Lennard-Jones fluids.
