Repeatable self-healing of a microcapsule-type protective coating

Cinnamide moiety-containing polydimethylsiloxane (CA-PDMS) was prepared and used as a healing agent. The photo-cross-linking behavior of CA-PDMS was investigated by UV-vis and Fourier transform infrared (FT-IR) spectroscopy. Upon photo-irradiation, CA-PDMS generates viscoelastic substances which have intrinsic recoating (or self-healing) capability when scribed with a cutter blade. CA-PDMS was microencapsulated with a urea-formaldehyde polymer, and the mean diameter and size distribution of the microcapsules could be controlled by the agitation rate. The prepared microcapsules were integrated into a commercial enamel paint to create a self-healing coating. It was confirmed by optical microscopy and scanning electron microscopy (SEM) that, when the self-healing coating is scribed, the healing agent is released from ruptured microcapsules and fills the scribed region. The scribed self-healing coating was photo-irradiated to induce photo-cross-linking of the released CA-PDMS. SEM imaging provided visual evidence that, when the scribed and healed region is re-scribed, repeated self-healing is accomplished. It was successfully demonstrated by anticorrosion and electrochemical tests that the CA-PDMS-based self-healing coating system has repeatable self-healing capability. Our self-healing coating is the first example of microcapsule-type repeatable self-healing system, and offers the advantages of simple, inexpensive, practical healing.