摩擦改进剂减摩作用的分子模拟研究

采用分子动力学（MD）和基于密度泛函理论（DFT）的量子化学方法，以油酸、油酸酰胺和二十四烷基环己烷为模型化合物，研究了3种分子与Fe〖DK〗(110)表面的物理/化学吸附作用和分子内聚能，分析了温度对吸附膜稳定性的影响。结果表明，油酸和油酸酰胺与Fe〖DK〗(110)表面通过范德华作用发生物理吸附，分子内通过范德华作用、静电作用和氢键作用结合，物理吸附能远大于分子内聚能，使它们能形成稳定的吸附膜。油酸和油酸酰胺的吸附能和内聚能均比环烷烃分子的高，因此在不同温度下能够形成更稳定的吸附膜。同时，酸和酰胺分子中的OC=O通过向Fe〖DK〗(110)表面提供电子发生化学吸附作用，而烃分子不会发生化学吸附，使油酸和油酸酰胺形成的吸附膜更加稳定。温度升高，分子的动能增加，不利于吸附过程的发生，会使吸附膜的稳定性下降，减摩作用减弱；同一温度下，环烷烃的动能比油酸和油酸酰胺的大，这也是油酸和油酸酰胺形成的吸附膜更加稳定的一个原因。

Molecular Simulation on Friction Reducing Performance of Friction Modifiers

The oleic acid, oleamide and tetracosyl cyclohexane were chosen as model compounds, and molecular dynamics (MD) and quantum chemistry (MC) based on density functional theory (DFT) were applied to study the physical and chemical adsorption energy of compounds with Fe(110) surfaces and the cohesive energy among molecules. The influence of temperature on the adsorption film was considered. The simulation results showed that oleic acid and oleamide adsorbed on the Fe(110) surfaces through van der Waals, and intra molecule forces through van der Waals, electrostatic and hydrogen bonding interaction. The adsorption energy was substantially higher than the cohesive energy, which made the adsorption film stable. The adsorption energy and cohesive energy of oleic acid and oleamide were higher than those of cycloalkane, so they could form more stable adsorption film. The OC=O of acid and amide could offer electron to the Fe(110) surfaces, and the molecules adsorbed on the surfaces by chemical interaction. The cycloalkane could not adsorb on the surfaces by chemical interaction, which made the adsorption film of oleic acid and oleamide more stable. The kinetic energy increased with the temperature increased, and the high temperature was bad for the adsorption process, so the stability of film would decrease when the temperature increased. Meanwhile, the kinetic energy of cycloalkane was more than that of oleic acid and oleamide at same temperature, which also was the reason that the adsorption film of oleic acid and oleamide were more stable than that of cycloalkane.