Effects of molecular structures of poly α-olefin mixture on nano-scale thin film lubrication

In order to determine how the molecular structures of poly α-olefin (PAO) mixture could impact the lubrication in nano-scale thin film, PAO models were constructed using the polymer of different polymerization degree according to published friction experiment, molecular dynamic simulations were conducted under compressed-shear condition. According to the simulation results, the PAO molecules with short side chains exhibited a rigid structure and high shear stress, while the molecules with long side chains exhibited the opposite and the tendency to orientate along the shearing direction. The syndiotactic molecular structure exhibited a lower friction coefficient than the isotactic structure. As suggested by the trajectory of lubricant molecules, the small lubricant molecules in the polymer mixture moved at a slower pace than the large ones under compressed-shear motion, indicating that the large molecules contribute more to the effect of friction than the small ones.