超薄润滑膜界面滑移现象的分子动力学研究

Molecular dynamics study of interfacial slip behavior of ultrathin lubricating films

为研究超薄润滑膜的流变和滑移特性 ,采用了分子动力学模拟方法。模拟系统由 2个固体壁面和介于壁面间的润滑剂分子构成 ,分子模型为正癸烷。结果表明 :薄膜中粒子密度沿膜厚方向呈周期性变化 ,存在某种有序结构 ;薄膜中润滑剂分子的平均速度仍大体呈线性分布 ,但在固液界面和液体层间可以观察到滑移现象 ;壁面滑移率随着剪切率的增加而上升 ,并在高剪切率区迅速增大 ;分子级薄膜中一个重要现象是滑移可能在较低的剪切率下发生 ;薄膜中润滑剂经历着向固态转化的相变过程 。

Rheology and slip property of ultrathin lubricating films were studied using molecular dynamics simulation. The model system consisted of two solid walls and the lubricant molecules confined between the walls. N decane was chosen to model the lubricant molecules. The results show that the particle density in the films periodically oscillates indicating a formation of layered structures. The simulation also show that the averaged velocities of the molecules are largely distributed linearly, but there is a slip velocity at the solid liquid interface. The slip ratio on the walls increasing with increasing shear rate and the increase is significant for very high shear rates. Another important phenomenon is that the wall slip may appear at low shear rates in molecularly thin films. A solidification process progresses in the thin films and the slip ratio at low shear rate may be considered as a convenient criterion to measure the solidification in lubricating films.