Abstract:

Molecular dynamics (MD) simulations using the polymer consistent force field (PCFF) were adopted to investigate the density, molecular and velocity distributions of lubricant squalane in nanogap at 293 K, three different film thicknesses and a wide range of shear velocities. The lubrication mechanism and boundary slip were analyzed. The results showed that the lubricant atoms tended to form layers parallel to the confining wall. The distances between the layers of lubricant atoms were irregular rather than broadening far away from the walls and were about three to four times the length of C-C bond in the squalane. The tendency of lubricant atoms to form layers and the density of solid-like layer increased with decreasing film thickness. It was clearly to find the boundary slip at the solid-liquid interface from the velocity profile. The slip lengths increased with increasing velocity of substrates at the beginning, and then decreased. When the film thickness was 3.44 nm, the maximum slip length was 4.35 nm at the substrate velocity of 22.8 m·s^-1. According to the simulations, the relationship between the slip length and the shear velocity was given.

Key words: molecular simulation, nanostructure, polymers, boundary slip, thin film lubrication, squalane

摘要：

采用聚合物一致性力场(PCFF),分别在7种剪切速度V和3种油膜厚度h下对纳米间隙中润滑剂角鲨烷进行分子动力学模拟,分析固液界面的密度、分子和流速的分布,探究纳米薄膜润滑的润滑机理和剪切速度对界面滑移的影响。结果表明,纳米间隙中润滑剂存在分层现象,各层间距相近,并非越远离固体壁面层间距越大,层间距约为角鲨烷分子单个C-C键距离的3~4倍;随着油膜厚度的减小,纳米间隙中润滑剂层状分布越明显,固化层密度越大;当油膜厚度为3.44 nm时,固液界面滑移现象明显,滑移长度b值随着V先增大后减小,当V为22.8 m·s^-1时,b达到最大值4.35 nm;根据模拟和计算结果,给出滑移长度与剪切速度的关系公式。

关键词: 分子模拟, 纳米结构, 聚合物, 界面滑移, 薄膜润滑, 角鲨烷