Novel fluorescent crack sensors have been developed based on dimeric anthracene moiety-containing polymers. Two anthracene derivatives, 9-anthraldehyde (AA) and 9-anthracenecarboxylic acid (AC), were photodimerized to obtain cyclooctane-type dimers. Crack-sensing polymers (Poly-AA and Poly-AC) were prepared by crosslinking of poly(vinyl alcohol) by using the dimers as crosslinkers. The polymers afforded transparent, hard coatings. Upon cracking, the polymers exhibited strong optical absorption and fluorescence emission while the uncracked original polymers did not. This was explained by regeneration of the anthracene moiety by mechanochemical cycloreversion of the cyclooctane dimer structure. It was found that the crack planes emitted fluorescence having emission maxima in the range of 500–600 nm when excited with 330–385 nm UV light. Absolute fluorescence quantum yield measurements indicated that the polymers could have good capability of fluorescence crack sensing. Preliminary evaluation of the crack-sensing ability of Poly-AA and Poly-AC was performed with the polymer films, and fluorescence emission was clearly observed along the crack planes upon excitation with 330–385 nm UV light. Poly-AA and Poly-AC are promising as fluorescent crack sensors because the anthracene moiety regenerated upon cracking has relatively long excitation and emission wavelengths as well as strong fluorescence.

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.

Linseed oil undergoes an oxidative drying reaction upon exposure to air, resulting in a soft film. The reaction conversion after 48 h reached 88% and 59% when it reacted at room temperature and −20 °C, respectively. Linseed-oil-loaded microcapsules were prepared using a urea-formaldehyde polymer as the shell wall material. The microcapsules were integrated into a commercially available protective coating formulation to prepare self-healing coating formulations with different capsule loadings. The coating formulations were applied on mortar specimens to prepare self-healing coatings. The effect of capsule loading on adhesion strength of the self-healing coating was studied. The self-healing function of the coating was investigated by SEM, a water sorptivity test and an accelerated carbonation test. Successful self-healing was demonstrated for both scratch and crack damage in the coatings. Low-temperature self-healing was demonstrated with a saline solution sorptivity test conducted at −20 °C. The linseed-oil-based microcapsule-type self-healing coating system is a promising candidate as a protective coating for cementitious materials.