薄膜润滑中固—液相变的模拟

Simulation of Solid-Liquid Transition in Thin Film Lubrication

本文以分子动力学方法模拟了薄膜润滑中润滑剂的固液相变。模拟系统由两个平行的固体壁面和界于壁面间的流体分子构成。薄膜中流体分子的运动规律可由系统运动方程解得,再通过平均得到薄膜液体的宏观特性。计算结果表明,在薄膜润滑中润滑剂的一些性质会变成与膜厚有关的参量,一定条件下还会发生由壁面诱发的相变。薄膜中润滑剂的相变临界压力随膜厚的减小而降低,当相变压力低于系统给定压力时,润滑剂会发生固化。这种现象与薄膜中有序结构的发展规律有关。随着压力增加,流体分子的有序结构由壁面逐渐向薄膜中部发展,因此较厚的润滑膜需要较高的压力才能形成贯穿全膜的有序结构而产生相变。

Solid-Liquid Transition of lubricant in ultra thin film has been simulated by molecular dynamics approach in the present study. The model system is composed of two parallel solid walls and confined fluid molecules. Time evolution of the fluid molecules can be obtained through solving the equation of motion. By averaging the molecule velocity in the system, the simulation gives macroscopic flow description. Results show that the some rheological parameters of the lubricant in thin film will become film thickness dependent and wall-induced phase transition may occure in the film under a certain condition. The critical pressure of the phase transition decreases as film thickness reducing. When transition pressure is lower than the pressure given by the system, liquid solidification will occure. The phenomenon is found relating to the development of the ordering structure in thin film.