Robust and impermeable metal shell microcapsules for one-component self-healing coatings

Metal shell microcapsules containing liquid 4,4′-bis-methylene cyclohexane diisocyanate (HMDI) were successfully synthesized by plating chemically a layer of Ni-P alloy on microcapsules surfaces. The metal shell occupied around 66.0 wt% of final microcapsules, providing great potential to improve microcapsules robustness. Final microcapsules with diameters of 184.3 ± 41.7 µm had a core fraction of 22.4 ± 0.6 wt%. The final microcapsule shells with a total thickness of 7.4 ± 0.4 µm was a three-layered structure, which comprised of an outer-layered Ni-P shell with a thickness of 5.5 ± 0.2 µm, a medium-layered PUF shell with a thickness of 369.0 ± 21.0 nm, and an inner-layered polyurea shell with a thickness of 1.7 ± 0.2 µm. More interestingly, final microcapsules remained stable core fraction and morphologies in most regular solvents including low polar organic solvents, high polar organic solvents, and water. The shell strength of final microcapsules was 28.5 ± 10.3 MPa, comparing with 6.6 ± 2.5 MPa of polymer shells. Moreover, the modulus of epoxy composites was stable relatively with microcapsules concentrations. Scratched self-healing epoxy coatings showed satisfactory anticorrosion performance in salty water (1 M).