Enhancing tribological, mechanical, and thermal properties of polyimide composites by the synergistic effect between graphene and ionic liquid

Developing self-lubricating composites with excellent tribological, thermal, and mechanical properties is a key aspect to solving the wear of materials. Herein, ionic liquid functionalized graphene (ILFG) were prepared by a π-π stacking interface design strategy. Then, a range of ILFG was filled into the polyimide (PI) matrix to prepare ILFG/PI composites (IGPI), and their tribological properties were investigated with a plate-on-ring apparatus under dry sliding conditions. When the content of ILFG was 0.4 wt%, the friction coefficient and specific wear rate of IGPI decreased by 38.2% and 25% compared to pure PI, respectively. A synergistic lubrication mechanism of ionic liquid (IL) and graphene was proposed for the formation of tribofilm under dry sliding. In addition, the mechanical and thermal properties of IGPI were also significantly improved by the synergy of IL and graphene. When the content of ILFG was 0.4 wt%, the tensile strength and modulus of IGPI composites increased by 51.9% and 56.5% relative to pure PI, respectively. The decomposition temperature of 5% weight loss (T5%) of IGPI with 0.4 wt% ILFG could reach 581.3 °C, an increase of 52.6 °C compared to that of PI, and the glass transition temperature improved by 14 °C.