School of Marine Science and Technology, Northwestern Polytechnical University, Xi'an, Shaanxi 710072, People's Republic of China.
Department of Mechanical and Materials Engineering, Wright State University, Dayton, Ohio 45435, USA.
Phys Rev E. 2017 Sep;96(3-1):033110. doi: 10.1103/PhysRevE.96.033110. Epub 2017 Sep 25.
Molecular dynamics simulations are used to investigate the rate and temperature dependence of the slip length in thin liquid films confined by smooth, thermal substrates. In our setup, the heat generated in a force-driven flow is removed by the thermostat applied on several wall layers away from liquid-solid interfaces. We found that for both high and low wall-fluid interaction (WFI) energies, the temperature of the fluid phase rises significantly as the shear rate increases. Surprisingly, with increasing shear rate, the slip length approaches a constant value from above for high WFI energies and from below for low WFI energies. The two distinct trends of the rate-dependent slip length are rationalized by examining S(G_{1}), the height of the main peak of the in-plane structure factor of the first fluid layer (FFL) together with D_{WF}, which is the average distance between the wall and FFL. The results of numerical simulations demonstrate that reduced values of the structure factor, S(G_{1}), correlate with the enhanced slip, while smaller distances D_{WF} indicate that fluid atoms penetrate deeper into the surface potential leading to larger friction and smaller slip. Interestingly, at the lowest WFI energy, the combined effect of the increase of S(G_{1}) and decrease of D_{WF} with increasing shear rate results in a dramatic reduction of the slip length.
采用分子动力学模拟方法研究了薄液膜在光滑热基底限制下的滑移长度对速度和温度的依赖性。在我们的模型中，通过在远离固液界面的几个壁层上施加恒温器来去除力驱动流动产生的热量。我们发现，对于高壁流相互作用（WFI）能和低壁流相互作用能，随着剪切速率的增加，流体相的温度都会显著升高。令人惊讶的是，随着剪切速率的增加，对于高 WFI 能，滑移长度从上方趋近于一个恒定值，而对于低 WFI 能，滑移长度从下方趋近于一个恒定值。通过检查第一流体层（FFL）中平面结构因子的主峰高度 S(G_{1})与 WF 之间的平均距离 D_{WF}，可以解释这种不同的速率依赖滑移长度的趋势。数值模拟结果表明，结构因子 S(G_{1})的降低与滑移的增强相关，而 D_{WF}的减小表明流体原子更深入地穿透表面势，导致更大的摩擦力和更小的滑移。有趣的是，在最低的 WFI 能下，随着剪切速率的增加，S(G_{1})的增加和 D_{WF}的减小的综合效应导致滑移长度的急剧减小。
