Robust SiO2/polymer hybrid microcapsule synthesized via emulsion photo-polymerization and its application in self-lubricating coatings

In this work, a novel kind of SiO2/polymer hybrid microcapsule encapsulating lubricant oil was prepared via a facile one-pot emulsion photo-polymerization method. In our strategy, an emulsion with the oil phase composed of SiO2 particles, photo-curable prepolymer, dichloromethane, photo-initiator and lubricant oil was firstly prepared. In the process of solvent evaporation, phase separation occurred between the photo-curable prepolymer and lubricant oil, and SiO2 particles migrated to the oil-water interface. After UV irradiation, the photo-curable prepolymer was photo-polymerized to form microcapsule shell, and SiO2/polymer hybrid microcapsule was yielded. The whole process could be finished within several minutes at room temperature, which was energy-saving and time-saving. The surface morphology of the microcapsule and the element distribution on the surface of the shell were investigated by SEM and EDS. The solvent resistance and mechanical property of hybrid microcapsules were tested. The morphology, the solvent resistance and the mechanical properties of SiO2/polymer hybrid microcapsule was controlled by adjusting the amount of SiO2 particles added in the oil phase. It was found that the introduction of SiO2 in the microcapsule shell could significantly improve the solvent resistance and mechanical properties of microcapsule. The synthesized hybrid microcapsule was embedded into epoxy resin for fabricating self-lubricating coatings. The friction and wear test results showed that the tribological property of the epoxy resin coating was significantly improved with the incorporation of the microcapsule. When the content of SiO2/polymer microcapsules was 10 wt%, the friction coefficient of the composite coating was 0.062, almost one-tenth of that of the pure epoxy coating (0.53).