Polydopamine-coated isocyanate microcapsules with enhanced water resistance for self-healing cement paste

The isocyanate system could directly react with water in the air to cure without adding curing agent, thus realizing self-healing, but it also limited its water resistance in humid environment. In this study, polydopamine was deposited on the surface of isocyanate microcapsules to improve their water resistance. Final microcapsules had a diameter of 322.1 ± 69.8 μm, a shell thickness of 6.5 ± 0.3 μm and a core content of 83.3 % ± 2.4 wt%. The optimum synthesis parameters for polydopamine doposition was dopamine concentration of 8.0 mg/ml, agitation rate of 300 rpm, and reaction duration of 24 h. After being immersed in ambient water for 28 days, the redisual core material of final microcapsules still remained at 15.0 wt%. Besides, the final microcapsules started to decompose at 240.0°C, indicating good thermal stability. The study also investigated the influence mechanism of microcapsules strength and interfacial strength on the mechanical properties of self-healing cement paste. At the same time, the total porosity of self-healing cement paste increased under higher microcapsule concentration. In addition, the self-healing cement paste could effectively repair cracks with width of about 100μm, showed good self-healing ability.