Study on Non-Newtonian Behaviors of Lennard-Jones Fluids via Molecular Dynamics Simulations

• Published in: Chinese journal of chemical physics 2016-12, Vol.29 (6), p.754-760
• Main Authors: Dong, Ruo-yu, Cao, Bing-yang, Yun, He-ming, Chen, Bao-ming
• Format: Article
• Language: English
• Subjects: Couette流; 分子动力学模拟; 剪切速率; 弹性模量; 径向分布函数; 振荡频率; 非牛顿特性; 高粘度流体
• ISSN: 1674-0068; 2327-2244
• DOI: 10.1063/1674-0068/29/cjcp1606129

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.