纳米间隙润滑剂季戊四醇四酯的压缩性能分子动力学模拟

Molecular Dynamics Simulation on the Compressibility of Pentaerythritol Tetra in Nanogap

季戊四醇四酯(Pentaerythritol tetra(2-ethylhexanoate),PETE)是良好的环境友好润滑剂。采用聚合物一致性力场(PCFF),分别在2种温度、3种初始油膜厚度和8种压力下对纳米间隙中PETE的压缩性能进行分子动力学模拟,研究润滑剂分子和密度的分布规律,并与经典宏观压缩试验得出的Tait方程计算值进行比较。结果表明,随着初始油膜厚度的增加,分子动力学模拟结果越接近Tait方程计算值,当初始油膜厚度为9.17 nm时,相对误差小于5%。在压缩过程中,油膜厚度和润滑剂的可压缩性能随着压力的增大而减小。对于不同初始油膜厚度的油膜,其压缩性能相近。由于PETE的分子结构中有较多且较长的支链,各方向尺度没有太大差异,受压缩后,除了接近固体壁面处有润滑剂原子聚集,其他地方不存在分层现象,且润滑剂与固体壁面之间不存在明显的空隙。

Pentaerythritol tetra （2-ethylhexanoate） （PETE） has been used as an environmentally friendly lubricant. Molecular dynamics （MD） simulations based on polymer consistent force field （PCFF） are adopted to investigate the molecule and density distributions of lubricant PETE in nanogap at two different temperatures, three different initial film thicknesses and a wide range of pressures. Results show that the densities of MD simulations are accurate to the values of Tait equation with the maximum initial film thickness （9.17nm）, the deviations are less than 5%. The film thickness and compressibility of films decrease with increasing pressure on the wall, but the compressibility is similar for films with different initial film thicknesses. Because the PETE molecule consists of four long branched chains, different spatial scales are in the same magnitude, the phenomenon of fluid atoms tending to form layers parallel to confining walls has not been observed except for the regions of lubricant adjacent walls. Distinct excluded volumes have not been found at the liquid/wall interfaces.