Stimuli-responsive oil release and improved tribological performance of flame sprayed polyamide coatings containing oil-encapsulated mesoporous silica microcapsules

Microcapsules made up of polyalphaolefin 40 (PAO40) core and silica (SiO2) shell were flame sprayed together with polyamide 11 (PA11) powders to fabricate the PA11/PAO40@SiO2 composite coating with improved tribological performance. Results showed that spherical PAO40@SiO2 microcapsules had mesoporous shell structure and good heat stability, and these microcapsules were distributed uniformly in the sprayed PA11/PAO40@SiO2 composite coating. PAO40 oil encapsulated inside microcapsules was released to the coating surface under external stimuli via pathways consisting of microcapsule mesopores and coating voids. The tribological performance of the PA11/PAO40@SiO2 composite coating was investigated under different mechanical loading conditions. Tribo-tests revealed that the friction coefficient of the composite coating decreased significantly with the increasing mechanical loading, presenting a trend opposite to the pure PA11 coating. Furthermore, the composite coating possessed much lower wear rate than the pure PA11 coating, and the enhanced oil release under the heavy load condition effectively protected the coating from premature failure. This work provides a novel strategy for developing smart polymer composite coatings with stimuli-responsive self-lubrication performance.