纳米液体润滑膜的分子动力学模拟──Ⅰ球型分子液体的模拟结果

MOLECULAR DYNAMICS SIMULATION OF NANO-SCALE LIQUID LUBRICATING FILMS──Ⅰ.Simulation results for the fluid with spherical molecule

固体表面间的润滑剂处于不同于体相液体的特殊约束状态．现以球型分子液体为模型对薄膜约束状态下润滑剂的性质进行分子动力学模拟结果表明，随着膜厚减薄，薄膜中液体等效粘度增加，固一液相变的临界压力减小，说明在纳米级薄膜中润滑剂可能在很低的压力下发生相变，从而表现出固体或类固体的性态在剪切响应方面，薄膜中润滑剂分子的松弛时间增加，在较低的剪切率下即出现剪切变稀现象。

Molecular dynamics simulation of confined lubricant has been performed in a spherical molecule model. Results show that as film thickness diminishing, the effective viscosity increases and the critical pressure of solid--liquid transition decreases. The results imply that in nano--scale films, lubricant may undergo a phase transition at a very low pressure and exhibits solid or solidlike behavior. The relaxation of lubricant molecules in thin films is proved much slower than in the bulk, leading to a shear thinning under lower shear rate, which means the lubricant confined in thin films shows strong no--Newtonian property and elastoviscosity. Simulation results for the alkane lubricant with chain molecules will be reported in the next paper.