PI-PDA@PSF@TO composite coating toward multifunctional development: Self-lubrication, self-healing, and heat-resistance

To facilitate versatile application of polyimide (PI) under harsh conditions, the PI-PDA@PSF@TO coating was successfully developed. The results illustrate the successful formation of PSF@TO microcapsules by encapsulating tung oil (TO) into polysulfone (PSF). After the modification of polydopamine (PDA), PDA@PSF@TO microcapsules exhibit superior dispersion within the coating compared to PSF@TO, resulting in a 16.8 % increase in tensile strength. Moreover, upon coating damage, the released TO can shield the samples in salt environment for a duration of 8 days. In comparison to PI, PI-PDA@PSF@TO coating exhibits a noteworthy decrease of 42.7 % in wear rate. Even after thermal oxidation, there is a noticeable reduction in the friction coefficient from 0.501 to 0.377, accompanied by a decrease in the wear rate from 6.33 × 10⁻⁷ mm³N⁻¹ m⁻¹ to 3.31 × 10⁻⁷ mm³N⁻¹ m⁻¹. This improvement contributes to two factors: (I) The PDA@PSF@TO microcapsules, developed by PSF and PDA, achieves the stable storage of TO in PI. (II) The release of TO forms protective layers, which compensate for defects and provide excellent tribological properties, thereby demonstrating the self-lubrication and self-healing characteristics.