A Computational Chemistry Approach for Investigation of Low Friction Mechanisms Based on FEP Film with Functionalized SiO<sub>2</sub> Nanoparticles

Abstract

To improve the fuel efficiency of automobile internal combustion engines, we investigated the fundamental mechanism of friction reduction within engine moving parts. A new coating was designed by introducing SiO2 nanoparticles in FEP film. The SiO2 nanoparticles were functionalized with hydrophobic fluoroalkyl units on their surface to create additional low friction property. Universal Surface Tester friction measurements revealed a significant reduction of the friction coefficient with increasing number of hydrophobic fluoroalkyl units for SiO2 surface functionalization. To clarify the friction reduction mechanisms by the functionalization of SiO2 nanoparticles, a quantum chemical calculation was carried out. The result indicates that an attractive force occurs between nanoparticle Si atoms and polymer F atoms, while by adding fluoroalkyl units on the SiO2 nanoparticle surface, this force changes to repulsive. By performing a molecular dynamics simulation of a shear model between FEP film and SiO2 nanoparticles, we observed a decrease of friction force with increasing fluoroalkyl units which lead smooth rolling motion of nanoparticles, thus confirming the repulsive effect of nanoparticle functionalization. We conclude that fluoroalkyl units on the SiO2 surface play an important role in creating a repulsive force between nanoparticle and FEP film which lead to low friction coefficient.