The effect of silica size on the friction and wear behaviors of polyimide/silica hybrids by sol-gel processing

In order to investigate the effect of silica size on the friction and wear behaviors of PI hybrids, polyimide/silica (PI/SiO2) hybrids with different size of silica were successfully synthesized through an in situ sol-gel reaction from pyromellitic dianhydride-4,4′-oxydianiline (PMDA-ODA) and tetraethoxysilane (TEOS). The size of silica in the hybrids was 100-800 nm. The friction and wear test for pure PI and its hybrids was carried out on a ball-on-disc wear tester under dry sliding conditions. Tensile tests on the PI/SiO2 hybrids showed that the strength and toughness of PI/SiO2 hybrids were improved simultaneously when the size of silica was less than 300 nm. The friction coefficient and wear rate of the PI hybrids firstly decreased and then increased with increasing the size of silica. The friction coefficient of the hybrid with 100 nm SiO2 was the lowest and ca.20% lower in contrast with that of pure PI. However, the lowest wear rate was recorded for the hybrid with 300 nm SiO2, ca.20% lower than that of neat PI. These behaviors were attributed to the size effect of silica in PI matrix. Scanning electron microscopy (SEM) revealed that an appropriate size of silica in PI matrix could effectively reduce adhesive wear of PI and restrain the formation of bigger debris.